U.S. patent application number 13/332054 was filed with the patent office on 2012-06-28 for using a most probable scanning order to efficiently code scanning order information for a video block in video coding.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Muhammed Zeyd Coban, Marta Karczewicz, Joel Sole Rojals, Yunfei Zheng.
Application Number | 20120163456 13/332054 |
Document ID | / |
Family ID | 45470729 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120163456 |
Kind Code |
A1 |
Coban; Muhammed Zeyd ; et
al. |
June 28, 2012 |
USING A MOST PROBABLE SCANNING ORDER TO EFFICIENTLY CODE SCANNING
ORDER INFORMATION FOR A VIDEO BLOCK IN VIDEO CODING
Abstract
In one example, an apparatus is disclosed for coding
coefficients associated with a block of video data during a video
coding process, the apparatus comprising a video coder configured
to code information that identifies a scanning order associated
with the block, wherein to code the information that identifies the
scanning order associated with the block, the video coder is
configured to determine a most probable scanning order for the
block, and code an indication of whether the scanning order
associated with the block is the most probable scanning order. In
another example, to code the information that identifies the
scanning order associated with the block, the video coder is
further configured to, in the event the scanning order associated
with the block is not the most probable scanning order, code an
indication of the scanning order associated with the block.
Inventors: |
Coban; Muhammed Zeyd;
(Carlsbad, CA) ; Zheng; Yunfei; (Cupertino,
CA) ; Sole Rojals; Joel; (La Jolla, CA) ;
Karczewicz; Marta; (San Diego, CA) |
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
45470729 |
Appl. No.: |
13/332054 |
Filed: |
December 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61426431 |
Dec 22, 2010 |
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61426426 |
Dec 22, 2010 |
|
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61547530 |
Oct 14, 2011 |
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Current U.S.
Class: |
375/240.13 ;
375/E7.243 |
Current CPC
Class: |
H04N 19/13 20141101;
H04N 19/176 20141101; H04N 19/70 20141101; H04N 19/129 20141101;
H04N 19/196 20141101; H04N 19/157 20141101; H04N 19/463 20141101;
H04N 19/46 20141101 |
Class at
Publication: |
375/240.13 ;
375/E07.243 |
International
Class: |
H04N 7/32 20060101
H04N007/32 |
Claims
1. A method of coding coefficients associated with a block of video
data during a video coding process, the method comprising: coding
information that identifies a scanning order associated with the
block, including determining a most probable scanning order for the
block, and coding an indication of whether the scanning order
associated with the block is the most probable scanning order.
2. The method of claim 1, wherein determining the most probable
scanning order for the block comprises determining a most probable
scanning order for the block based on a prediction mode and a size
associated with the block.
3. The method of claim 1, wherein coding the indication of whether
the scanning order associated with the block is the most probable
scanning order comprises performing a context adaptive entropy
coding process that includes applying a context model based on at
least one context, wherein the at least one context includes one of
the most probable scanning order, a prediction mode associated with
the block, and a size associated with the block.
4. The method of claim 1, further comprising: in the event the
scanning order associated with the block is not the most probable
scanning order, using a zig-zag scanning order to code the
coefficients associated with the block.
5. The method of claim 1, wherein coding the information that
identifies the scanning order associated with the block further
includes: in the event the scanning order associated with the block
is not the most probable scanning order, coding an indication of
the scanning order associated with the block.
6. The method of claim 5, wherein coding the indication of the
scanning order associated with the block comprises performing a
context adaptive entropy coding process that includes applying a
context model based on at least one context, wherein the at least
one context includes one of the most probable scanning order, a
prediction mode associated with the block, and a size associated
with the block.
7. The method of claim 1, wherein determining the most probable
scanning order for the block comprises designating a zig-zag
scanning order as the most probable scanning order for the
block.
8. The method of claim 1, wherein each of the scanning order
associated with the block and the most probable scanning order
comprises one of a zig-zag scanning order, a horizontal scanning
order, a vertical scanning order, and a diagonal scanning
order.
9. The method of claim 1, further comprising coding information
that identifies a position of a last non-zero coefficient within
the block according to the scanning order associated with the
block.
10. The method of claim 1, further comprising coding information
that identifies positions of non-zero coefficients within the
block.
11. An apparatus for coding coefficients associated with a block of
video data during a video coding process, the apparatus comprising
a video coder configured to: code information that identifies a
scanning order associated with the block, wherein to code the
information that identifies the scanning order associated with the
block, the video coder is configured to determine a most probable
scanning order for the block, and code an indication of whether the
scanning order associated with the block is the most probable
scanning order.
12. The apparatus of claim 11, wherein to determine the most
probable scanning order for the block, the video coder is
configured to determine a most probable scanning order for the
block based on a prediction mode and a size associated with the
block.
13. The apparatus of claim 11, wherein to code the indication of
whether the scanning order associated with the block is the most
probable scanning order, the video coder is configured to perform a
context adaptive entropy coding process that includes the video
coder applying a context model based on at least one context,
wherein the at least one context includes one of the most probable
scanning order, a prediction mode associated with the block, and a
size associated with the block.
14. The apparatus of claim 11, wherein the video coder is further
configured to: in the event the scanning order associated with the
block is not the most probable scanning order, use a zig-zag
scanning order to code the coefficients associated with the
block.
15. The apparatus of claim 11, wherein to code the information that
identifies the scanning order associated with the block, the video
coder is further configured to: in the event the scanning order
associated with the block is not the most probable scanning order,
code an indication of the scanning order associated with the
block.
16. The apparatus of claim 15, wherein to code the indication of
the scanning order associated with the block, the video coder is
configured to perform a context adaptive entropy coding process
that includes the video coder applying a context model based on at
least one context, wherein the at least one context includes one of
the most probable scanning order, a prediction mode associated with
the block, and a size associated with the block.
17. The apparatus of claim 11, wherein to determine the most
probable scanning order for the block, the video coder is
configured to designate a zig-zag scanning order as the most
probable scanning order for the block.
18. The apparatus of claim 11, wherein each of the scanning order
associated with the block and the most probable scanning order
comprises one of a zig-zag scanning order, a horizontal scanning
order, a vertical scanning order, and a diagonal scanning
order.
19. The apparatus of claim 11, wherein the video coder is further
configured to code information that identifies a position of a last
non-zero coefficient within the block according to the scanning
order associated with the block.
20. The apparatus of claim 11, wherein the video coder is further
configured to code information that identifies positions of
non-zero coefficients within the block.
21. The apparatus of claim 11, wherein the apparatus comprises at
least one of: an integrated circuit; a microprocessor; and a
wireless communication device that includes the video coder.
22. A device for coding coefficients associated with a block of
video data during a video coding process, the device comprising:
means for coding information that identifies a scanning order
associated with the block, including means for determining a most
probable scanning order for the block, and means for coding an
indication of whether the scanning order associated with the block
is the most probable scanning order.
23. The device of claim 22, wherein the means for determining the
most probable scanning order for the block comprises means for
determining a most probable scanning order for the block based on a
prediction mode and a size associated with the block.
24. The device of claim 22, wherein the means for coding the
indication of whether the scanning order associated with the block
is the most probable scanning order comprises means for performing
a context adaptive entropy coding process that includes applying a
context model based on at least one context, wherein the at least
one context includes one of the most probable scanning order, a
prediction mode associated with the block, and a size associated
with the block.
25. The device of claim 22, further comprising: means for, in the
event the scanning order associated with the block is not the most
probable scanning order, using a zig-zag scanning order to code the
coefficients associated with the block.
26. The device of claim 22, wherein the means for coding the
information that identifies the scanning order associated with the
block further includes: means for, in the event the scanning order
associated with the block is not the most probable scanning order,
coding an indication of the scanning order associated with the
block.
27. The device of claim 26, wherein the means for coding the
indication of the scanning order associated with the block
comprises means for performing a context adaptive entropy coding
process that includes applying a context model based on at least
one context, wherein the at least one context includes one of the
most probable scanning order, a prediction mode associated with the
block, and a size associated with the block.
28. The device of claim 22, wherein the means for determining the
most probable scanning order for the block comprises means for
designating a zig-zag scanning order as the most probable scanning
order for the block.
29. The device of claim 22, wherein each of the scanning order
associated with the block and the most probable scanning order
comprises one of a zig-zag scanning order, a horizontal scanning
order, a vertical scanning order, and a diagonal scanning
order.
30. The device of claim 22, further comprising means for coding
information that identifies a position of a last non-zero
coefficient within the block according to the scanning order
associated with the block.
31. The device of claim 22, further comprising means for coding
information that identifies positions of non-zero coefficients
within the block.
32. A computer-readable medium comprising instructions that, when
executed, cause a processor to code coefficients associated with a
block of video data during a video coding process, wherein the
instructions cause the processor to: code information that
identifies a scanning order associated with the block, wherein the
instructions that cause the processor to code the information that
identifies the scanning order associated with the block comprise
instructions that cause the processor to determine a most probable
scanning order for the block, and code an indication of whether the
scanning order associated with the block is the most probable
scanning order.
33. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to determine the most
probable scanning order for the block comprise instructions that
cause the processor to determine a most probable scanning order for
the block based on a prediction mode and a size associated with the
block.
34. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to code the indication of
whether the scanning order associated with the block is the most
probable scanning order comprise instructions that cause the
processor to perform a context adaptive entropy coding process that
includes applying a context model based on at least one context,
wherein the at least one context includes one of the most probable
scanning order, a prediction mode associated with the block, and a
size associated with the block.
35. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to code the coefficients
associated with the block during the video coding process further
cause the processor to: in the event the scanning order associated
with the block is not the most probable scanning order, use a
zig-zag scanning order to code the coefficients associated with the
block.
36. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to code the information that
identifies the scanning order associated with the block further
comprise instructions that cause the processor to: in the event the
scanning order associated with the block is not the most probable
scanning order, code an indication of the scanning order associated
with the block.
37. The computer-readable medium of claim 36, wherein the
instructions that cause the processor to code the indication of the
scanning order associated with the block comprise instructions that
cause the processor to perform a context adaptive entropy coding
process that includes applying a context model based on at least
one context, wherein the at least one context includes one of the
most probable scanning order, a prediction mode associated with the
block, and a size associated with the block.
38. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to determine the most
probable scanning order for the block comprise instructions that
cause the processor to designate a zig-zag scanning order as the
most probable scanning order for the block.
39. The computer-readable medium of claim 32, wherein each of the
scanning order associated with the block and the most probable
scanning order comprises one of a zig-zag scanning order, a
horizontal scanning order, a vertical scanning order, and a
diagonal scanning order.
40. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to code the coefficients
associated with the block during the video coding process further
cause the processor to: code information that identifies a position
of a last non-zero coefficient within the block according to the
scanning order associated with the block.
41. The computer-readable medium of claim 32, wherein the
instructions that cause the processor to code the coefficients
associated with the block during the video coding process further
cause the processor to: code information that identifies positions
of non-zero coefficients within the block.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/426,431, filed Dec. 22, 2010, U.S. Provisional
Application No. 61/426,426, filed Dec. 22, 2010, and U.S.
Provisional Application No. 61/547,530, filed Oct. 14, 2011, the
entire contents of each of which are incorporated herein by
reference.
TECHNICAL FIELD
[0002] This disclosure relates to video coding, and more
particularly, to the coding of syntax information related to
coefficients of a video block.
BACKGROUND
[0003] Digital video capabilities can be incorporated into a wide
range of devices, including digital televisions, digital direct
broadcast systems, wireless broadcast systems, personal digital
assistants (PDAs), laptop or desktop computers, tablet computers,
e-book readers, digital cameras, digital recording devices, digital
media players, video gaming devices, video game consoles, cellular
or satellite radio telephones, so-called "smart phones," video
teleconferencing devices, video streaming devices, and the like.
Digital video devices implement video compression techniques, such
as those described in the standards defined by MPEG-2, MPEG-4,
ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding
(AVC), the High Efficiency Video Coding (HEVC) standard presently
under development, and extensions of such standards. The video
devices may transmit, receive, encode, decode, and/or store digital
video information more efficiently by implementing such video
compression techniques.
[0004] Video compression techniques perform spatial (intra-picture)
prediction and/or temporal (inter-picture) prediction to reduce or
remove redundancy inherent in video sequences. For block-based
video coding, a video slice (i.e., a video frame or a portion of a
video frame) may be partitioned into video blocks, which may also
be referred to as treeblocks, coding units (CUs) and/or coding
nodes. Video blocks in an intra-coded (I) slice of a picture are
encoded using spatial prediction with respect to reference samples
in neighboring blocks in the same picture. Video blocks in an
inter-coded (P or B) slice of a picture may use spatial prediction
with respect to reference samples in neighboring blocks in the same
picture or temporal prediction with respect to reference samples in
other reference pictures. Pictures may be referred to as frames,
and reference pictures may be referred to as reference frames.
[0005] Spatial or temporal prediction results in a predictive block
for a block to be coded. Residual data represents pixel differences
between the original block to be coded and the predictive block. An
inter-coded block is encoded according to a motion vector that
points to a block of reference samples forming the predictive
block, and the residual data indicating the difference between the
coded block and the predictive block. An intra-coded block is
encoded according to an intra-coding mode and the residual data.
For further compression, the residual data may be transformed from
the pixel domain to a transform domain, resulting in residual
transform coefficients, which then may be quantized. The quantized
transform coefficients, initially arranged in a two-dimensional
array, may be scanned in order to produce a one-dimensional vector
of transform coefficients, and entropy coding may be applied to
achieve even more compression.
SUMMARY
[0006] This disclosure describes techniques for coding coefficients
associated with a block of video data during a video coding
process, including techniques for coding information that
identifies a scanning order associated with the block, i.e.,
scanning order information for the block. The techniques of this
disclosure may improve efficiency for coding of scanning order
information for blocks of video data used to code the blocks by
coding scanning order information for a particular block using
information that identifies a most probable scanning order for the
block. In other words, the techniques may improve compression of
the scanning order information for the blocks when the information
is coded.
[0007] In one example, the coding efficiency may be improved by
determining a most probable scanning order for a block of video
data, and coding an indication of whether the scanning order
associated with the block, i.e., the scanning order used to code
the block, is the most probable scanning order. In this example, in
the event the scanning order associated with the block is the most
probable scanning order, no further scanning order information may
be coded for the block. In the event the scanning order associated
with the block is not the most probable scanning order, however,
the techniques may further include coding an indication of the
scanning order associated with the block. Because, by definition, a
most probable scanning order for a particular block of video data
will, on average, be used to code the block more often than any
other scanning order that also may be used to code the block, the
additional indication of the scanning order associated with the
block will not be coded in numerous cases. As a result, the
scanning order information for the block may be coded using less
information than when using other techniques, e.g., when always
coding the scanning order information for the block in its
entirety.
[0008] As another example, the coding efficiency may be improved
by, in the event the scanning order associated with the block is
not the most probable scanning order, using a zig-zag scanning
order to code the coefficients associated with the block. Once
again, because, by definition, a most probable scanning order for a
particular block of video data will, on average, be used to code
the block more often than any other scanning order that also may be
used to code the block, the initial indication of whether the
scanning order associated with the block is the most probable
scanning order will indicate the scanning order information for the
block in its entirety in numerous cases, obviating the need for
coding any further scanning order information. Furthermore, in the
event the scanning order associated with the block is not the most
probable scanning order, not coding an indication of the scanning
order associated with the block, but rather using the zig-zag
scanning order to code the coefficients associated with the block,
may be sufficient to efficiently code the block. For example, any
adverse effects of using the zig-zag scanning order to code the
coefficients, rather than using another scanning order that may
more efficiently scan the coefficients, may be outweighed by the
reduced coding of the scanning order information for the block
described above.
[0009] As still another example, the coding efficiency may be
improved by designating the zig-zag scanning order as the most
probable scanning order for the block. In this example, because the
zig-zag scanning order may, on average, be used to code the block
more often than any other scanning order that also may be used to
code the block, the additional indication of the scanning order
associated with the block may not be coded in numerous cases.
Furthermore, by designating the zig-zag scanning order as the most
probable scanning order, the coding efficiency may be improved by
avoiding determining an actual most probable scanning order for the
block, as described above.
[0010] In each of the examples described above, the coding
efficiency may be further improved by entropy coding the scanning
order information for the block, i.e., one or more of the
indication of whether the scanning order associated with the block
is the most probable scanning order, and the indication of the
scanning order associated with the block. For example, the scanning
order information may be entropy coded by performing a context
adaptive entropy coding process, e.g., a context adaptive binary
arithmetic coding (CABAC) process that includes applying a context
model based on at least one context. In the examples described
above, the at least one context may include one of the most
probable scanning order, a prediction mode associated with the
block, and a size associated with the block, which may result in
probability estimates included within the context model being more
accurate relative to probability estimates determined using other
techniques. A result, the scanning order information for the block
may be coded more efficiently. For example, the information may be
coded using fewer bits than when using other techniques, e.g., when
using other, less accurate probability estimates to code the
information.
[0011] The techniques of this disclosure may, in some examples, be
used with any context adaptive entropy coding methodology,
including CABAC, probability interval partitioning entropy coding
(PIPE), or another context adaptive entropy coding methodology.
CABAC is described in this disclosure for purposes of illustration,
but without limitation as to the techniques broadly described in
this disclosure. Also, the techniques may be applied to coding of
other types of data generally, e.g., in addition to video data.
[0012] Accordingly, the techniques of this disclosure may enable
using more efficient coding methods relative to other methods when
coding scanning order information for one or more blocks of video
data. In this manner, there may be a relative bit savings for a
coded bitstream including the information when using the techniques
of this disclosure.
[0013] In one example, a method of coding coefficients associated
with a block of video data during a video coding process includes
coding information that identifies a scanning order associated with
the block, including determining a most probable scanning order for
the block, and coding an indication of whether the scanning order
associated with the block is the most probable scanning order.
[0014] In another example, an apparatus for coding coefficients
associated with a block of video data during a video coding process
includes a video coder configured to code information that
identifies a scanning order associated with the block, wherein to
code the information that identifies the scanning order associated
with the block, the video coder is configured to determine a most
probable scanning order for the block, and code an indication of
whether the scanning order associated with the block is the most
probable scanning order.
[0015] In another example, a device for coding coefficients
associated with a block of video data during a video coding process
includes means for coding information that identifies a scanning
order associated with the block, including means for determining a
most probable scanning order for the block, and means for coding an
indication of whether the scanning order associated with the block
is the most probable scanning order.
[0016] The techniques described in this disclosure may be
implemented in hardware, software, firmware, or combinations
thereof. If implemented in hardware, an apparatus may be realized
as an integrated circuit, a processor, discrete logic, or any
combination thereof. If implemented in software, the software may
be executed in one or more processors, such as a microprocessor,
application specific integrated circuit (ASIC), field programmable
gate array (FPGA), or digital signal processor (DSP). The software
that executes the techniques may be initially stored in a tangible
computer-readable medium and loaded and executed in the
processor.
[0017] Accordingly, this disclosure also contemplates a
computer-readable medium comprising instructions that, when
executed, cause a processor to code coefficients associated with a
block of video data during a video coding process, wherein the
instructions cause the processor to code information that
identifies a scanning order associated with the block, wherein the
instructions that cause the processor to code the information that
identifies the scanning order associated with the block comprise
instructions that cause the processor to determine a most probable
scanning order for the block, and code an indication of whether the
scanning order associated with the block is the most probable
scanning order.
[0018] The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a block diagram that illustrates an example of a
video encoding and decoding system that may implement techniques
for using a most probable scanning order to efficiently code
scanning order information for a block of video data, consistent
with the techniques of this disclosure.
[0020] FIG. 2 is a block diagram that illustrates an example of a
video encoder that may implement techniques for using a most
probable scanning order to efficiently encode scanning order
information for a block of video data, consistent with the
techniques of this disclosure.
[0021] FIG. 3 is a block diagram that illustrates an example of a
video decoder that may implement techniques for using a most
probable scanning order to efficiently decode encoded scanning
order information for a block of video data, consistent with the
techniques of this disclosure.
[0022] FIGS. 4A-4C are conceptual diagrams that illustrate an
example of a block of video data and corresponding significant
coefficient position information and last significant coefficient
position information.
[0023] FIGS. 5A-5C are conceptual diagrams that illustrate examples
of blocks of video data scanned using a zig-zag scanning order, a
horizontal scanning order, and a vertical scanning order.
[0024] FIGS. 6A-6B are conceptual diagrams that illustrate examples
of blocks video data having various sizes, and examples of blocks
of video data for which various prediction modes are used to
generate prediction data, consistent with the techniques of this
disclosure.
[0025] FIG. 7 is a flowchart that illustrates an example of a
method for using a most probable scanning order to efficiently code
scanning order information for a block of video data, consistent
with the techniques of this disclosure.
[0026] FIG. 8 is a flowchart that illustrates an example of a
method for using a most probable scanning order to efficiently
encode scanning order information for a block of video data,
consistent with the techniques of this disclosure.
[0027] FIG. 9 is a flowchart that illustrates an example of a
method for using a most probable scanning order to efficiently
decode encoded scanning order information for a block of video
data, consistent with the techniques of this disclosure.
DETAILED DESCRIPTION
[0028] This disclosure describes techniques for coding coefficients
associated with a block of video data during a video coding
process, including techniques for coding information that
identifies a scanning order associated with the block, i.e.,
scanning order information for the block. The techniques of this
disclosure may improve efficiency for coding of scanning order
information for blocks of video data used to code the blocks by
coding scanning order information for a particular block using
information that identifies a most probable scanning order for the
block. In other words, the techniques may improve compression of
the scanning order information for the blocks when the scanning
order information is coded.
[0029] In this disclosure, the term "coding" refers to encoding
that occurs at the encoder or decoding that occurs at the decoder.
Similarly, the term coder refers to an encoder, a decoder, or a
combined encoder/decoder (CODEC). The terms coder, encoder, decoder
and CODEC all refer to specific machines designed for the coding
(encoding and/or decoding) of video data consistent with this
disclosure.
[0030] In general, empirical testing performed in development of
these techniques has demonstrated a correlation between a
prediction mode and a size associated with a block of video data,
and a scanning order associated with the block, i.e., the scanning
order used to code the block. For example, the scanning order
associated with the block may depend on the prediction mode used to
generate prediction data for the block, and on the size of the
block. In other words, a particular scanning order may be used to
code the block more often than any other scanning order that also
may be used to code the block, depending on a prediction mode and a
size associated with the block.
[0031] Coding efficiency for coding of scanning order information
for blocks of video data used to code the blocks may be improved by
taking advantage of the above-described correlation. Specifically,
the coding efficiency may be improved by coding scanning order
information for a particular block using information that
identifies a most probable scanning order for the block. In some
examples, a most probable scanning order for a particular block may
be determined based on an intra-prediction mode and a size
associated with the block. For example, an encoder and a decoder
may both be programmed to define the most probable scanning order
for the block based on the intra-prediction mode and the size
associated with the block, and information can be signaled by the
encoder to indicate to the decoder whether the most probable
scanning order was actually used by the encoder to encode the
block.
[0032] In one example, the coding efficiency may be improved by
determining a most probable scanning order for a block of video
data, and coding an indication of whether the scanning order
associated with the block, i.e., the scanning order used to code
the block, is the most probable scanning order. In this example, in
the event the scanning order associated with the block is the most
probable scanning order, no further scanning order information may
be coded for the block. In the event the scanning order associated
with the block is not the most probable scanning order, however,
the techniques may further include coding an indication of the
scanning order associated with the block. Because, by definition, a
most probable scanning order for a particular block of video data
will, on average, be used to code the block more often than any
other scanning order that also may be used to code the block, the
additional indication of the scanning order associated with the
block will not be coded in numerous cases. As a result, the
scanning order information for the block may be coded using less
information than when using other techniques, e.g., when always
coding the scanning order information for the block in its
entirety.
[0033] As another example, the coding efficiency may be improved
by, in the event the scanning order associated with the block is
not the most probable scanning order, using a zig-zag scanning
order to code the coefficients associated with the block. Once
again, because, by definition, a most probable scanning order for a
particular block of video data will, on average, be used to code
the block more often than any other scanning order that also may be
used to code the block, the initial indication of whether the
scanning order associated with the block is the most probable
scanning order will indicate the scanning order information for the
block in its entirety in numerous cases, obviating the need for
coding any further scanning order information. Furthermore, in the
event the scanning order associated with the block is not the most
probable scanning order, not coding an indication of the scanning
order associated with the block, but rather using the zig-zag
scanning order to code the coefficients associated with the block,
may be sufficient to efficiently code the block. For example, any
adverse effects of using the zig-zag scanning order to code the
coefficients, rather than using another scanning order that may
more efficiently scan the coefficients, may be outweighed by the
reduced coding of the scanning order information for the block
described above.
[0034] As still another example, the coding efficiency may be
improved by designating the zig-zag scanning order as the most
probable scanning order for the block. In this example, because the
zig-zag scanning order may, on average, be used to code the block
more often than any other scanning order that also may be used to
code the block, the additional indication of the scanning order
associated with the block may not be coded in numerous cases.
Furthermore, by designating the zig-zag scanning order as the most
probable scanning order, the coding efficiency may be improved by
avoiding determining an actual most probable scanning order for the
block, as described above.
[0035] In each of the examples described above, the coding
efficiency may be further improved by entropy coding the scanning
order information for the block, i.e., one or more of the
indication of whether the scanning order associated with the block
is the most probable scanning order, and the indication of the
scanning order associated with the block. For example, the scanning
order information may be entropy coded by performing a context
adaptive entropy coding process, e.g., a context adaptive binary
arithmetic coding (CABAC) process that includes applying a context
model based on at least one context. In the examples described
above, the at least one context may include one of the most
probable scanning order, a prediction mode associated with the
block, and a size associated with the block, which may result in
probability estimates included within the context model being more
accurate relative to probability estimates determined using other
techniques. A result, the scanning order information for the block
may be coded more efficiently. For example, the information may be
coded using fewer bits than when using other techniques, e.g., when
using other, less accurate probability estimates to code the
information.
[0036] Coding scanning order information for one or more blocks of
video data in the manner described above may enable using more
efficient coding methods relative to other methods. In this manner,
there may be a relative bit savings for a coded bitstream including
the information when using the techniques of this disclosure.
[0037] The techniques of this disclosure may, in some examples, be
used with any context adaptive entropy coding methodology,
including CABAC, probability interval partitioning entropy coding
(PIPE), or another context adaptive entropy coding methodology.
CABAC is described in this disclosure for purposes of illustration,
but without limitation as to the techniques broadly described in
this disclosure. Also, the techniques may be applied to coding of
other types of data generally, e.g., in addition to video data.
[0038] FIG. 1 is a block diagram that illustrates an example of a
video encoding and decoding system 10 that may implement techniques
for using a most probable scanning order to efficiently code
scanning order information for a block of video data, consistent
with the techniques of this disclosure. As shown in FIG. 1, system
10 includes a source device 12 that transmits encoded video to a
destination device 14 via a communication channel 16. Source device
12 and destination device 14 may comprise any of a wide range of
devices. In some cases, source device 12 and destination device 14
may comprise wireless communication devices, such as wireless
handsets, so-called cellular or satellite radiotelephones, or any
wireless devices that can communicate video information over a
communication channel 16, in which case communication channel 16 is
wireless.
[0039] The techniques of this disclosure, however, which concern
using a most probable scanning order to efficiently code scanning
order information for a block of video data, are not necessarily
limited to wireless applications or settings. These techniques may
generally apply to any scenario where encoding or decoding is
performed, including over-the-air television broadcasts, cable
television transmissions, satellite television transmissions,
streaming Internet video transmissions, encoded digital video that
is encoded onto a storage medium or retrieved and decoded from a
storage medium, or other scenarios. Accordingly, communication
channel 16 is not required and the techniques of this disclosure
may apply to settings where encoding is applied or where decoding
is applied, e.g., without any data communication between encoding
and decoding devices.
[0040] In the example of FIG. 1, source device 12 includes a video
source 18, video encoder 20, a modulator/demodulator (modem) 22 and
a transmitter 24. Destination device 14 includes a receiver 26, a
modem 28, a video decoder 30, and a display device 32. In
accordance with this disclosure, video encoder 20 of source device
12 and/or video decoder 30 of destination device 14 may be
configured to apply the techniques for using a most probable
scanning order to efficiently code scanning order information for a
block of video data. In other examples, a source device and a
destination device may include other components or arrangements.
For example, source device 12 may receive video data from an
external video source 18, such as an external camera. Likewise,
destination device 14 may interface with an external display
device, rather than including an integrated display device.
[0041] The illustrated system 10 of FIG. 1 is merely one example.
Techniques for using a most probable scanning order to efficiently
code scanning order information for a block of video data may be
performed by any digital video encoding and/or decoding device.
Although generally the techniques of this disclosure are performed
by a video encoding device, the techniques may also be performed by
a video encoder/decoder, typically referred to as a "CODEC."
Moreover, the techniques of this disclosure may also be performed
by a video preprocessor. Source device 12 and destination device 14
are merely examples of such coding devices in which source device
12 generates coded video data for transmission to destination
device 14. In some examples, devices 12, 14 may operate in a
substantially symmetrical manner such that each of devices 12, 14
includes video encoding and decoding components. Hence, system 10
may support one-way or two-way video transmission between video
devices 12, 14, e.g., for video streaming, video playback, video
broadcasting, or video telephony.
[0042] Video source 18 of source device 12 may include a video
capture device, such as a video camera, a video archive containing
previously captured video, and/or a video feed from a video content
provider. As a further alternative, video source 18 may generate
computer graphics-based data as the source video, or a combination
of live video, archived video, and computer-generated video. In
some cases, if video source 18 is a video camera, source device 12
and destination device 14 may form so-called camera phones or video
phones. As mentioned above, however, the techniques described in
this disclosure may be applicable to video coding in general, and
may be applied to wireless and/or wired applications. In each case,
the captured, pre-captured, or computer-generated video may be
encoded by video encoder 20. The encoded video information may then
be modulated by modem 22 according to a communication standard, and
transmitted to destination device 14 via transmitter 24. Modem 22
may include various mixers, filters, amplifiers or other components
designed for signal modulation. Transmitter 24 may include circuits
designed for transmitting data, including amplifiers, filters, and
one or more antennas.
[0043] Receiver 26 of destination device 14 receives information
over channel 16, and modem 28 demodulates the information. Again,
the video encoding process described above may implement one or
more of the techniques described herein to use a most probable
scanning order to efficiently code scanning order information for a
block of video data. The information communicated over channel 16
may include syntax information defined by video encoder 20, which
is also used by video decoder 30, that includes syntax elements
that describe characteristics and/or processing of blocks of video
data (e.g., macroblocks, or coding units), e.g., scanning order
information for the blocks, and other information. Display device
32 displays the decoded video data to a user, and may comprise any
of a variety of display devices such as a cathode ray tube (CRT), a
liquid crystal display (LCD), a plasma display, an organic light
emitting diode (OLED) display, or another type of display
device.
[0044] In the example of FIG. 1, communication channel 16 may
comprise any wireless or wired communication medium, such as a
radio frequency (RF) spectrum or one or more physical transmission
lines, or any combination of wireless and wired media.
Communication channel 16 may form part of a packet-based network,
such as a local area network, a wide-area network, or a global
network such as the Internet. Communication channel 16 generally
represents any suitable communication medium, or collection of
different communication media, for transmitting video data from
source device 12 to destination device 14, including any suitable
combination of wired or wireless media. Communication channel 16
may include routers, switches, base stations, or any other
equipment that may be useful to facilitate communication from
source device 12 to destination device 14. In other examples,
encoding or decoding devices may implement techniques of this
disclosure without any communication between such devices. For
example, an encoding device may encode and store an encoded
bitstream consistent with the techniques of this disclosure.
Alternatively, a decoding device may receive or retrieve an encoded
bitstream, and decode the bitstream consistent with the techniques
of this disclosure.
[0045] Video encoder 20 and video decoder 30 may operate according
to a video compression standard, such as the ITU-T H.264 standard,
alternatively referred to as MPEG-4, Part 10, Advanced Video Coding
(AVC). The techniques of this disclosure, however, are not limited
to any particular coding standard. Other examples include MPEG-2,
ITU-T H.263, and the High Efficiency Video Coding (HEVC) standard
presently under development. In general, the techniques of this
disclosure are described with respect to HEVC, but it should be
understood that these techniques may be used in conjunction with
other video coding standards as well. Although not shown in FIG. 1,
in some aspects, video encoder 20 and video decoder 30 may each be
integrated with an audio encoder and decoder, and may include
appropriate MUX-DEMUX units, or other hardware and software, to
handle encoding of both audio and video in a common data stream or
separate data streams. If applicable, MUX-DEMUX units may conform
to the ITU H.223 multiplexer protocol, or other protocols such as
the user datagram protocol (UDP).
[0046] Video encoder 20 and video decoder 30 each may be
implemented as any of a variety of suitable encoder and decoder
circuitry, such as one or more microprocessors, digital signal
processors (DSPs), application specific integrated circuits
(ASICs), field programmable gate arrays (FPGAs), discrete logic,
software, hardware, firmware or any combinations thereof. Each of
video encoder 20 and video decoder 30 may be included in one or
more encoders or decoders, either of which may be integrated as
part of a combined encoder/decoder (CODEC) in a respective camera,
computer, mobile device, subscriber device, broadcast device,
set-top box, server, or the like.
[0047] A video sequence typically includes a series of video
frames. A group of pictures (GOP) generally comprises a series of
one or more video frames. A GOP may include syntax data in a header
of the GOP, a header of one or more frames of the GOP, or
elsewhere, that describes a number of frames included in the GOP.
Each frame may include frame syntax data that describes an encoding
mode for the respective frame. A video encoder, e.g., video encoder
20, typically operates on video blocks within individual video
frames in order to encode the video data. According to the ITU-T
H.264 standard, a video block may correspond to a macroblock or a
partition of a macroblock. According to other standards, e.g., HEVC
described in greater detail below, a video block may correspond to
a coding unit (e.g., a largest coding unit), or a partition of a
coding unit. The video blocks may have fixed or varying sizes, and
may differ in size according to a specified coding standard. Each
video frame may include a plurality of slices, i.e., portions of
the video frame. Each slice may include a plurality of video
blocks, which may be arranged into partitions, also referred to as
sub-blocks.
[0048] Depending on the specified coding standard, video blocks may
be partitioned into various "N.times.N" sub-block sizes, such as
16.times.16, 8.times.8, 4.times.4, 2.times.2, and so forth. In this
disclosure, "N.times.N" and "N by N" may be used interchangeably to
refer to the pixel dimensions of the block in terms of vertical and
horizontal dimensions, e.g., 16.times.16 pixels or 16 by 16 pixels.
In general, a 16.times.16 block will have sixteen pixels in a
vertical direction (y=16) and sixteen pixels in a horizontal
direction (x=16). Likewise, an N.times.N block generally has N
pixels in a vertical direction and N pixels in a horizontal
direction, where N represents a nonnegative integer value. The
pixels in a block may be arranged in rows and columns. Moreover,
blocks need not necessarily have the same number of pixels in the
horizontal direction as in the vertical direction. For example,
blocks may comprise N.times.M pixels, where M is not necessarily
equal to N. As one example, in the ITU-T H.264 standard, blocks
that are 16 by 16 pixels in size may be referred to as macroblocks,
and blocks that are less than 16 by 16 pixels may be referred to as
partitions of a 16 by 16 macroblock. In other standards, e.g.,
HEVC, blocks may be defined more generally with respect to their
size, for example, as coding units and partitions thereof, each
having a varying, rather than a fixed size.
[0049] Video blocks may comprise blocks of pixel data in the pixel
domain, or blocks of transform coefficients in the transform
domain, e.g., following application of a transform, such as a
discrete cosine transform (DCT), an integer transform, a wavelet
transform, or a conceptually similar transform to residual data for
a given video block, wherein the residual data represents pixel
differences between video data for the block and predictive data
generated for the block. In some cases, video blocks may comprise
blocks of quantized transform coefficients in the transform domain,
wherein, following application of a transform to residual data for
a given video block, the resulting transform coefficients are also
quantized.
[0050] Block partitioning serves an important purpose in
block-based video coding techniques. Using smaller blocks to code
video data may result in better prediction of the data for
locations of a video frame that include high levels of detail, and
may therefore reduce the resulting error (i.e., deviation of the
prediction data from source video data), represented as residual
data. While potentially reducing the residual data, such techniques
may, however, require additional syntax information to indicate how
the smaller blocks are partitioned relative to a video frame, and
may result in an increased coded video bitrate. Accordingly, in
some techniques, block partitioning may depend on balancing the
desirable reduction in residual data against the resulting increase
in bitrate of the coded video data due to the additional syntax
information.
[0051] In general, blocks and the various partitions thereof (i.e.,
sub-blocks) may be considered video blocks. In addition, a slice
may be considered to be a plurality of video blocks (e.g.,
macroblocks, or coding units), and/or sub-blocks (partitions of
marcoblocks, or sub-coding units). Each slice may be an
independently decodable unit of a video frame. Alternatively,
frames themselves may be decodable units, or other portions of a
frame may be defined as decodable units. Furthermore, a GOP, also
referred to as a sequence, may be defined as a decodable unit.
[0052] Efforts are currently in progress to develop a new video
coding standard, currently referred to as High Efficiency Video
Coding (HEVC). The emerging HEVC standard may also be referred to
as H.265. The standardization efforts are based on a model of a
video coding device referred to as the HEVC Test Model (HM). The HM
presumes several capabilities of video coding devices over devices
according to, e.g., ITU-T H.264/AVC. For example, whereas H.264
provides nine intra-prediction encoding modes, HM provides as many
as thirty-five intra-prediction encoding modes, e.g., based on the
size of a block being intra-prediction coded.
[0053] HM refers to a block of video data as a coding unit (CU). A
CU may refer to a rectangular image region that serves as a basic
unit to which various coding tools are applied for compression. In
H.264, it may also be called a macroblock. Syntax data within a
bitstream may define a largest coding unit (LCU), which is a
largest CU in terms of the number of pixels. In general, a CU has a
similar purpose to a macroblock of H.264, except that a CU does not
have a size distinction. Thus, a CU may be partitioned, or "split"
into sub-CUs.
[0054] An LCU may be associated with a quadtree data structure that
indicates how the LCU is partitioned. In general, a quadtree data
structure includes one node per CU of an LCU, where a root node
corresponds to the LCU, and other nodes correspond to sub-CUs of
the LCU. If a given CU is split into four sub-CUs, the node in the
quadtree corresponding to the split CU includes four child nodes,
each of which corresponds to one of the sub-CUs. Each node of the
quadtree data structure may provide syntax information for the
corresponding CU. For example, a node in the quadtree may include a
split flag for the CU, indicating whether the CU corresponding to
the node is split into four sub-CUs. Syntax information for a given
CU may be defined recursively, and may depend on whether the CU is
split into sub-CUs.
[0055] A CU that is not split (i.e., a CU corresponding a terminal,
or "leaf" node in a given quadtree) may include one or more
prediction units (PUs). In general, a PU represents all or a
portion of the corresponding CU, and includes data for retrieving a
reference sample for the PU for purposes of performing prediction
for the CU. For example, when the CU is intra-mode encoded, the PU
may include data describing an intra-prediction mode for the PU. As
another example, when the CU is inter-mode encoded, the PU may
include data defining a motion vector for the PU. The data defining
the motion vector may describe, for example, a horizontal component
of the motion vector, a vertical component of the motion vector, a
resolution for the motion vector (e.g., one-quarter pixel precision
or one-eighth pixel precision), a reference frame to which the
motion vector points, and/or a reference list (e.g., list 0 or list
1) for the motion vector. Data for the CU defining the one or more
PUs of the CU may also describe, for example, partitioning of the
CU into the one or more PUs. Partitioning modes may differ between
whether the CU is uncoded, intra-prediction mode encoded, or
inter-prediction mode encoded.
[0056] A CU having one or more PUs may also include one or more
transform units (TUs). Following prediction for a CU using one or
more PUs, as described above, a video encoder may calculate one or
more residual blocks for the respective portions of the CU
corresponding to the one of more PUs. The residual blocks may
represent a pixel difference between the video data for the CU and
the predicted data for the one or more PUs. A set of residual
values may be transformed, scanned, and quantized to define a set
of quantized transform coefficients. A TU may define a partition
data structure that indicates partition information for the
transform coefficients that is substantially similar to the
quadtree data structure described above with reference to a CU. A
TU is not necessarily limited to the size of a PU. Thus, TUs may be
larger or smaller than corresponding PUs for the same CU. In some
examples, the maximum size of a TU may correspond to the size of
the corresponding CU. In one example, residual samples
corresponding to a CU may be subdivided into smaller units using a
quadtree structure known as "residual quad tree" (RQT). In this
case, the leaf nodes of the RQT may be referred as the TUs, for
which the corresponding residual samples may be transformed and
quantized.
[0057] Following intra-predictive or inter-predictive encoding to
produce predictive data and residual data, and following any
transforms (such as the 4.times.4 or 8.times.8 integer transform
used in H.264/AVC or a discrete cosine transform DCT) to produce
transform coefficients, quantization of transform coefficients may
be performed. Quantization generally refers to a process in which
transform coefficients are quantized to possibly reduce the amount
of data used to represent the coefficients. The quantization
process may reduce the bit depth associated with some or all of the
coefficients. For example, an n-bit value may be rounded down to an
m-bit value during quantization, where n is greater than m.
[0058] Following quantization, entropy coding of the quantized data
(i.e., quantized transform coefficients) may be performed. The
entropy coding may conform to the techniques of this disclosure
with respect to using a most probable scanning order to efficiently
code scanning order information for a block of video data, and may
also use other entropy coding techniques, such as context adaptive
variable length coding (CAVLC), CABAC, PIPE, or another entropy
coding methodology. For example, coefficient values, represented as
magnitudes and corresponding signs (e.g., "+1," or "-1") for the
quantized transform coefficients may be encoded using the entropy
coding techniques.
[0059] It should be noted that the prediction, transform, and
quantization described above may be performed for any block of
video data, e.g., to a PU and/or TU of a CU, or to a macroblock,
depending on the specified coding standard. Accordingly, the
techniques of this disclosure, relating to using a most probable
scanning order to efficiently code scanning order information for a
block of video data, may apply to any block of video data, e.g., to
any block of quantized transform coefficients, including a
macroblock, or a TU of a CU. Furthermore, a block of video data
(e.g., a macroblock, or a TU of a CU) may include each of a
luminance component (Y), a first chrominance component (U), and a
second chrominance component (V) of the corresponding video data.
As such, the techniques of this disclosure may be performed for
each of the Y, U, and V components of a given block of video
data.
[0060] In order to encode blocks of video data as described above,
information regarding position of significant coefficients within a
given block may also be generated and encoded. Subsequently, the
values of the significant coefficients may be encoded, as described
above. In H.264/AVC and the emerging HEVC standard, when using a
context adaptive entropy coding process, e.g., a CABAC process, the
position of significant coefficients within a block of video data
may be encoded prior to encoding the values of the significant
coefficients. The process of encoding the position of all of the
significant coefficients within the block may be referred to as
significance map (SM) encoding. FIGS. 4A-4C, described in greater
detail below, are conceptual diagrams that illustrate an example of
a 4.times.4 block of quantized transform coefficients and
corresponding SM data.
[0061] A typical SM encoding procedure may be described as follows.
For a given block of video data, an SM may be encoded only if there
is at least one significant coefficient within the block. Presence
of significant coefficients within a given block of video data may
be indicated in a coded block pattern (e.g., using syntax element
"coded_block_pattern," or CBP), which is a binary value coded for a
set of blocks (such as luminance and chrominance blocks) associated
with an area of pixels in the video data. Each bit in the CBP is
referred to as a coded block flag (e.g., corresponding to syntax
element "coded_block_flag") and used to indicate whether there is
at least one significant coefficient within its corresponding
block. In other words, a coded block flag is a one-bit symbol
indicating whether there are any significant coefficients inside a
single block of transform coefficients, and a CBP is a set of coded
block flags for a set of related video data blocks.
[0062] If a coded block flag indicates that no significant
coefficients are present within the corresponding block (e.g., the
flag equals "0"), no further information may be encoded for the
block. However, if a coded block flag indicates that at least one
significant coefficient exists within the corresponding block
(e.g., the flag equals "1"), an SM may be encoded for the block by
following a coefficient scanning order associated with the block.
The scanning order may define the order in which the significance
of each coefficient within the block is encoded as part of the SM
encoding. In other words, scanning may serialize the
two-dimensional block of coefficients to a one-dimensional
representation to determine the significance of the coefficients.
Different scanning orders (e.g., zigzag, horizontal, and vertical)
may be used. FIGS. 5A-5C, also described in greater detail below,
illustrate examples of some of the various scanning orders that may
be used for 8.times.8 blocks of video data. The techniques of this
disclose, however, may also apply with respect to a wide variety of
other scanning orders, including a diagonal scanning order,
scanning orders that are combinations of zigzag, horizontal,
vertical, and/or diagonal scanning orders, as well as scanning
orders that are partially zigzag, partially horizontal, partially
vertical, and/or partially diagonal. In addition, the techniques of
this disclosure may also consider a scanning order that is itself
adaptive based on statistics associated with previously coded
blocks of video data (e.g., blocks having the same block size or
coding mode as the current block being coded). For example, an
adaptive scanning order could be the most probable scanning order
in some cases.
[0063] Given a coded block flag that indicates that at least one
significant coefficient exists within a given block, and a scanning
order for the block, an SM for the block may be encoded as follows.
The two-dimensional block of quantized transform coefficients may
first be mapped into a one-dimensional array using the scanning
order. For each coefficient in the array, following the scanning
order, a one-bit significant coefficient flag (e.g., corresponding
to syntax element "significant_coeff_flag") may be encoded. That
is, each position in the array may be assigned a binary value,
which may be set to "1" if the corresponding coefficient is
significant, and set to "0" if it is non-significant (i.e.,
zero).
[0064] If a given significant coefficient flag equals "1,"
indicating that the corresponding coefficient is significant, an
additional one-bit last significant coefficient flag (e.g.,
corresponding to syntax element "last_significant_coeff_flag") may
also be encoded, which may indicate whether the corresponding
coefficient is the last significant coefficient within the array
(i.e., within the block given the scanning order). Specifically,
each last significant coefficient flag may be set to "1" if the
corresponding coefficient is the last significant coefficient
within the array, and set to "0" otherwise. If the last array
position is reached in this manner, and the SM encoding process was
not terminated by a last significant coefficient flag equal to "1,"
then the last coefficient in the array (and thereby the block given
the scanning order) may be inferred to be significant, and no last
significant coefficient flag may be encoded for the last array
position.
[0065] FIGS. 4B-4C are conceptual diagrams that illustrate examples
of sets of significant coefficient flags and last significant
coefficient flags, respectively, corresponding to SM data for the
block depicted in FIG. 4A, presented in map, rather than array
form. It should be noted that significant coefficient flags and
last significant coefficient flags, as described above, may be set
to different values (e.g., a significant coefficient flag may be
set to "0" if the corresponding coefficient is significant, and "1"
if it is non-significant, and a last significant coefficient flag
may be set to "0" if the corresponding coefficient is the last
significant coefficient, and "1" if it is not the last significant
coefficient) in other examples.
[0066] After the SM is encoded, as described above, the value of
each significant coefficient (i.e., each significant coefficient's
magnitude and sign, e.g., indicated by syntax elements
"coeff_abs_level_minus1" and "coeff_sign_flag," respectively) in
the block may also be encoded.
[0067] According to some techniques, a fixed scanning order may be
used to code blocks of video data, as described above, e.g., the
zig-zag scanning order. According to other techniques, multiple
scanning orders may be used to code the blocks. In some examples,
"adaptive coefficient scanning" (ACS) may be used, wherein the
scanning order adapts over time, and the currently adapted scanning
order is used to code a particular block of coefficients at any
given time. In still other techniques, video encoder 20 may test
several scanning orders based on one or more compression efficiency
metrics and select the best scanning order to encode the blocks.
Additionally, video encoder 20 may indicate the scanning order to
video decoder 30 by encoding an ACS index, which may represent any
one of the several scanning orders (e.g., using indices 0 for
zig-zag, 1 for horizontal, and 2 for vertical scanning orders).
[0068] According to some techniques, video encoder 20 may encode
the ACS index only when the last significant coefficient is not
located in the first position in the scanning order (corresponding
to the top-left position within the block commonly referred to as
the "DC" position). Video encoder 20 may encode the ACS index in
this manner because video decoder 30 does not need an indication of
the scanning order used by video encoder 20 in the case the last
(and only) significant coefficient within the block is located in
the DC position, since all possible scanning orders may start with
the DC position, as shown in FIG. 5, also described in greater
detail below.
[0069] In the event the last significant coefficient within the
block is not located in the DC position, video encoder 20 may
encode the ACS index in the following manner. Video encoder 20 may
encode a first signal (e.g., "bin1") that indicates whether the
scanning order is the zig-zag scanning order (e.g., bin1="0") or
not (e.g., bin1="1"). In the event the scanning order is not the
zig-zag scanning order, video encoder 20 may encode a second signal
(e.g., "bin2") that indicates whether the scanning order is the
horizontal scanning order (e.g., bin2="0") or the vertical scanning
order (e.g., bin2="1"). Similarly, video decoder 30 may receive and
decode the first signal and the second signal to determine the ACS
index. Accordingly, rather than always coding the ACS index, video
encoder 20 and/or video decoder 30 may code the ACS index only when
the last significant coefficient is not located in the DC
position.
[0070] One drawback of the techniques described above is that, when
coding scanning order information for a block of video data, video
encoder 20 and/or video decoder 30 may always code the information
in its entirety. In other words, video encoder 20 and/or video
decoder 30 may always code the entire scanning order information
for the block, for example, using one to two bits, or "bins,"
depending on the scanning order associated with the block, i.e.,
the scanning order used to code the block. Furthermore, when video
encoder 20 and/or video decoder 30 code the scanning order
information for the block, the techniques described above fail to
take advantage of a correlation among a prediction mode and a size
associated with the block, and a scanning order associated with the
block, i.e., the scanning order used to code the block. In these
cases, always coding the scanning order information for the block
in its entirety, and coding the information without taking
advantage of the above-described correlation, may result in coding
the information less efficiently, e.g., using more bins, than when
using other techniques to code the information.
[0071] Another drawback of the techniques described above is that,
when video encoder 20 and/or video decoder 30 further entropy code
the scanning order information for the block, e.g., represented
using one to two bins, by performing a context adaptive entropy
coding process (e.g., a CABAC process), the techniques may use
context models that contain probability estimates that are less
accurate than probability estimates determined using other methods.
Entropy coding the scanning order information for the block using
such probability estimates may once again result in coding the
information less efficiently, for example, using more bits, than
when using other techniques, e.g., using more accurate probability
estimates to entropy code the information.
[0072] Accordingly, this disclosure describes techniques that may
enable coding scanning order information for a block of video data
more efficiently relative to other techniques. As one example, the
scanning order information may be coded more efficiently by
determining a most probable scanning order for the block, and
coding an indication of whether the scanning order associated with
the block, i.e., the scanning order used to code the block, is the
most probable scanning order. In the event the scanning order
associated with the block is the most probable scanning order, no
further scanning order information may be coded for the block. In
the event the scanning order associated with the block is not the
most probable scanning order, however, the techniques may further
include coding an indication of the scanning order associated with
the block. Because, by definition, a most probable scanning order
for a particular block of video data will, on average, be used to
code the block more often than any other scanning order that also
may be used to code the block, the additional indication of the
scanning order associated with the block will not be coded in
numerous cases. As a result, the scanning order information for the
block may be coded using less information than when using other
techniques.
[0073] As another example, the scanning order information may be
coded more efficiently by, in the event the scanning order
associated with the block is not the most probable scanning order,
using a zig-zag scanning order to code the coefficients associated
with the block. Once again, because, by definition, a most probable
scanning order for a particular block of video data will, on
average, be used to code the block more often than any other
scanning order that also may be used to code the block, the initial
indication of whether the scanning order associated with the block
is the most probable scanning order will indicate the scanning
order information for the block in its entirety in numerous cases,
obviating the need for coding any further scanning order
information. Furthermore, in the event the scanning order
associated with the block is not the most probable scanning order,
not coding an indication of the scanning order associated with the
block, but rather using the zig-zag scanning order to code the
coefficients associated with the block, may be sufficient to
efficiently code the block. For example, any adverse effects of
using the zig-zag scanning order to code the coefficients, rather
than using another scanning order that may more efficiently scan
the coefficients, may be outweighed by the reduced coding of the
scanning order information for the block described above.
[0074] As still another example, the scanning order information may
be coded more efficiently by designating the zig-zag scanning order
as the most probable scanning order for the block. In this example,
because the zig-zag scanning order may, on average, be used to code
the block more often than any other scanning order that also may be
used to code the block, the additional indication of the scanning
order associated with the block may not be coded in numerous cases.
Furthermore, by designating the zig-zag scanning order as the most
probable scanning order, the coding efficiency may be improved by
avoiding determining an actual most probable scanning order for the
block, as described above.
[0075] In each of the examples described above, the scanning order
information may be coded more efficiently by further entropy coding
the scanning order information for the block, i.e., one or more of
the indication of whether the scanning order associated with the
block is the most probable scanning order, and the indication of
the scanning order associated with the block. For example, the
scanning order information may be entropy coded by performing a
context adaptive entropy coding process (e.g., a CABAC process)
that includes applying a context model based on at least one
context. In the examples described above, the at least one context
may include one of the most probable scanning order, a prediction
mode associated with the block, and a size associated with the
block, which may result in probability estimates included within
the context model being more accurate relative to probability
estimates determined using other techniques. A result, the scanning
order information for the block may be coded more efficiently. For
example, the information may be coded using fewer bits than when
using other techniques, e.g., when using other, less accurate
probability estimates to code the information.
[0076] In the examples described above, the most probable scanning
order may be defined at the encoder and the decoder based on a
coding mode used to code the block and a size associated with the
block. The coding mode may be one of an intra-prediction mode and
an inter-prediction mode, although these techniques may be most
applicable to blocks coded using intra-prediction modes. Thus, in
some examples the determination of the most probable scanning order
may be based on which of a plurality of intra-prediction modes is
used to code the block. The size associated with the block may
refer to a CU size, a PU size, a TU size, or possibly even some
combination of CU, PU and/or TU sizes associated with the
block.
[0077] It should be noted that the techniques of this disclosure
are applicable to any method of coding scanning order information
for a block of video data, including the techniques for SM coding
described above, as well as other techniques for coding the
scanning order information. For example, the techniques of this
disclosure may include coding scanning order information for a
block of video data in the manner described herein independently of
the SM data (i.e., last significant coefficient position
information and the significant coefficient position information)
for the block. As one example, the techniques may include coding
the scanning order information after coding the last significant
coefficient position information, and prior to coding the
significant coefficient position information, for the block.
[0078] In some examples, video encoder 20 of source device 12 may
be configured to encode certain blocks of video data (e.g., one or
more macroblocks, or TUs of a CU), and video decoder 30 of
destination device 14 may be configured to receive the encoded
video data from video encoder 20, e.g., from modem 28 and receiver
26. In accordance with the techniques of this disclosure, as one
example, video encoder 20 and/or video decoder 30 may be configured
to code information that identifies a scanning order associated
with the block, i.e., the scanning order information for the block.
For example, video encoder 20 and/or video decoder 30 may be
configured to determine a most probable scanning order for the
block, and code an indication of whether the scanning order
associated with the block is the most probable scanning order. In
this example, each of the scanning order associated with the block
and the most probable scanning order may comprise one of a zig-zag
scanning order, a horizontal scanning order, and a vertical
scanning order. Again, the zig-zag, horizontal, and vertical
scanning orders are merely examples, and other scanning orders may
also be defined or used consistent with the techniques of this
disclosure.
[0079] To determine the most probable scanning order for the block,
video encoder 20 and/or video decoder 30 may be configured to
determine a most probable scanning order for the block based on a
prediction mode and a size associated with the block, as described
in greater detail below with reference to FIGS. 6A-6B.
[0080] Furthermore, to code the indication of whether the scanning
order associated with the block is the most probable scanning
order, video encoder 20 and/or video decoder 30 may be configured
to perform a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on at least
one context. For example, the at least one context may include one
of the most probable scanning order, a prediction mode associated
with the block, and a size associated with the block.
[0081] In another example, to code the scanning order information
for the block, video encoder 20 and/or video decoder 30 may be
further configured to, in the event the scanning order associated
with the block is not the most probable scanning order, code an
indication of the scanning order associated with the block.
[0082] In this example, to code the indication of the scanning
order associated with the block, video encoder 20 and/or video
decoder 30 may once again be configured to perform a context
adaptive entropy coding process (e.g., a CABAC process) that
includes video encoder 20 and/or video decoder 30 applying a
context model based on at least one context. For example, the at
least one context may once again include one of the most probable
scanning order, the prediction mode associated with the block, and
the size associated with the block.
[0083] Accordingly, in this example, video encoder 20 and/or video
decoder 30 may be configured to code the scanning order information
for the block by coding the indication of whether the scanning
order associated with the block is the most probable scanning
order, and, in some cases, the indication of the scanning order
associated with the block.
[0084] In another example, to code the scanning order information
for the block, video encoder 20 and/or video decoder 30 may be
further configured to, in the event the scanning order associated
with the block is not the most probable scanning order, use a
zig-zag scanning order to code the coefficients associated with the
block. Accordingly, in this example, after determining the most
probable scanning order for the block, and coding the indication of
whether the scanning order associated with the block is the most
probable scanning order, video encoder 20 and/or video decoder 30
may be configured to not code any additional scanning order
information for the block.
[0085] In still another example, to determine the most probable
scanning order for the block, video encoder 20 and/or video decoder
30 may be configured to designate a zig-zag scanning order as the
most probable scanning order for the block. In this example, in a
similar manner as described above, to code the scanning order
information for the block, video encoder 20 and/or video decoder 30
may be further configured to, in the event the scanning order
associated with the block is not the most probable scanning order
(i.e., in this particular example, the zig-zag scanning order),
code an indication of the scanning order associated with the block.
In other words, in this example, video encoder 20 and/or video
decoder 30 may be configured to presume the zig-zag scanning order
to be the most probable scanning order for the block, rather than
perform an actual determination of the most probable scanning order
for the block, e.g., using scanning order information for
previously coded blocks.
[0086] In this example, to code the indication of the scanning
order associated with the block, video encoder 20 and/or video
decoder 30 may once again be configured to perform a context
adaptive entropy coding process (e.g., a CABAC process) that
includes video encoder 20 and/or video decoder 30 applying a
context model based on at least one context. For example, the at
least one context may once again include one of the most probable
scanning order, the prediction mode associated with the block, and
the size associated with the block.
[0087] Accordingly, in this example, video encoder 20 and/or video
decoder 30 may be configured to code the scanning order information
for the block by coding the indication of whether the scanning
order associated with the block is the zig-zag scanning order, and,
in some cases, the indication of the scanning order associated with
the block.
[0088] In this example, video encoder 20 and/or video decoder 30
may be further configured to code information that identifies a
position of a last non-zero coefficient within the block according
to the scanning order associated with the block, i.e., the last
significant coefficient position information for the block.
Additionally, video encoder 20 and/or video decoder 30 may be
further configured to code information that identifies positions of
all other non-zero coefficients within the block, i.e., significant
coefficient position information for the block. As previously
described, the last significant coefficient position information
and the significant coefficient position information for the block
may be collectively referred to as SM data for the block.
[0089] In any case, after coding the scanning order information,
and the last significant coefficient position information and the
significant coefficient position information, i.e., the SM data,
for the block in the manner described above, video encoder 20
and/or video decoder 30 may also code the value of each significant
coefficient (e.g., each significant coefficient's magnitude and
sign, indicated by syntax elements "coeff_abs_level_minus1" and
"coeff_sign_flag," respectively) within the block.
[0090] Accordingly, the techniques of this disclosure may enable
video encoder 20 and/or video decoder 30 to code the scanning order
information for the block more efficiently than when using other
methods. In this manner, there may be a relative bit savings for a
coded bitstream including the scanning order information when using
the techniques of this disclosure.
[0091] Video encoder 20 and video decoder 30 each may be
implemented as any of a variety of suitable encoder or decoder
circuitry, as applicable, such as one or more microprocessors,
digital signal processors (DSPs), application specific integrated
circuits (ASICs), field programmable gate arrays (FPGAs), discrete
logic circuitry, software, hardware, firmware or any combinations
thereof. Each of video encoder 20 and video decoder 30 may be
included in one or more encoders or decoders, either of which may
be integrated as part of a combined video encoder/decoder (CODEC).
An apparatus including video encoder 20 and/or video decoder 30 may
comprise an integrated circuit, a microprocessor, and/or a wireless
communication device, such as a cellular telephone.
[0092] FIG. 2 is a block diagram that illustrates an example of a
video encoder 20 that may implement techniques for using a most
probable scanning order to efficiently encode scanning order
information for a block of video data, consistent with the
techniques of this disclosure. Video encoder 20 may perform intra-
and inter-coding of blocks within video frames, including
macroblocks, CUs, and partitions or sub-partitions thereof.
Intra-coding relies on spatial prediction to reduce or remove
spatial redundancy in video within a given video frame.
Inter-coding relies on temporal prediction to reduce or remove
temporal redundancy in video within adjacent frames of a video
sequence. Intra-mode (I-mode) may refer to any of several spatial
based compression modes, and inter-modes, such as uni-directional
prediction (P-mode) or bi-directional prediction (B-mode), may
refer to any of several temporal-based compression modes.
[0093] As shown in FIG. 2, video encoder 20 receives a current
block of video data within a video frame to be encoded. In the
example of FIG. 2, video encoder 20 includes motion compensation
unit 44, motion estimation unit 42, memory 64, summer 50, transform
module 52, quantization unit 54, and entropy encoding unit 56. For
video block reconstruction, video encoder 20 also includes inverse
quantization unit 58, inverse transform module 60, and summer 62. A
deblocking filter (not shown in FIG. 2) may also be included to
filter block boundaries to remove blockiness artifacts from
reconstructed video. If desired, the deblocking filter would
typically filter the output of summer 62.
[0094] During the encoding process, video encoder 20 receives a
video frame or slice to be coded. The frame or slice may be divided
into multiple video blocks. Motion estimation unit 42 and motion
compensation unit 44 may perform inter-predictive coding of a given
received video block relative to one or more blocks in one or more
reference frames to provide temporal compression. Intra-prediction
module 46 may perform intra-predictive coding of a given received
video block relative to one or more neighboring blocks in the same
frame or slice as the block to be coded to provide spatial
compression.
[0095] Mode select unit 40 may select one of the coding modes,
i.e., one mode or multiple intra- or inter-coding modes, based on
coding results (e.g., resulting coding rate and level of
distortion), and based on a frame or slice type for the frame or
slice including the given received block being coded, and provide
the resulting intra- or inter-coded block to summer 50 to generate
residual block data and to summer 62 to reconstruct the encoded
block for use in a reference frame or reference slice. In general,
intra-prediction involves predicting a current block relative to
neighboring, previously coded blocks, while inter-prediction
involves motion estimation and motion compensation to temporally
predict the current block.
[0096] Motion estimation unit 42 and motion compensation unit 44
represent the inter-prediction elements of video encoder 20. Motion
estimation unit 42 and motion compensation unit 44 may be highly
integrated, but are illustrated separately for conceptual purposes.
Motion estimation is the process of generating motion vectors,
which estimate motion for video blocks. A motion vector, for
example, may indicate the displacement of a predictive block within
a predictive reference frame (or other coded unit) relative to the
current block being coded within the current frame (or other coded
unit). A predictive block is a block that is found to closely match
the block to be coded, in terms of pixel difference, which may be
determined by sum of absolute difference (SAD), sum of square
difference (SSD), or other difference metrics. A motion vector may
also indicate displacement of a partition of a block. Motion
compensation may involve fetching or generating the predictive
block based on the motion vector determined by motion estimation.
Again, motion estimation unit 42 and motion compensation unit 44
may be functionally integrated, in some examples.
[0097] Motion estimation unit 42 may calculate a motion vector for
a video block of an inter-coded frame by comparing the video block
to video blocks of a reference frame in memory 64. Motion
compensation unit 44 may also interpolate sub-integer pixels of the
reference frame, e.g., an I-frame or a P-frame, for the purposes of
this comparison. The ITU H.264 standard, as an example, describes
two lists: list 0, which includes reference frames having a display
order earlier than a current frame being encoded, and list 1, which
includes reference frames having a display order later than the
current frame being encoded. Therefore, data stored in memory 64
may be organized according to these lists.
[0098] Motion estimation unit 42 may compare blocks of one or more
reference frames from memory 64 to a block to be encoded of a
current frame, e.g., a P-frame or a B-frame. When the reference
frames in memory 64 include values for sub-integer pixels, a motion
vector calculated by motion estimation unit 42 may refer to a
sub-integer pixel location of a reference frame. Motion estimation
unit 42 and/or motion compensation unit 44 may also be configured
to calculate values for sub-integer pixel positions of reference
frames stored in memory 64 if no values for sub-integer pixel
positions are stored in memory 64. Motion estimation unit 42 may
send the calculated motion vector to entropy encoding unit 56 and
motion compensation unit 44. The reference frame block identified
by a motion vector may be referred to as an inter-predictive block,
or, more generally, a predictive block. Motion compensation unit 44
may calculate prediction data based on the predictive block.
[0099] Intra-prediction module 46 may intra-predict a current
block, as an alternative to the inter-prediction performed by
motion estimation unit 42 and motion compensation unit 44, as
described above. In particular, intra-prediction module 46 may
determine an intra-prediction mode to use to encode a current
block. In some examples, intra-prediction module 46 may encode a
current block using various intra-prediction modes, e.g., during
separate encoding passes, and intra-prediction module 46 (or mode
select unit 40, in some examples) may select an appropriate
intra-prediction mode to use from the tested modes. For example,
intra-prediction module 46 may calculate rate-distortion values
using a rate-distortion analysis for the various tested
intra-prediction modes, and select the intra-prediction mode having
the best rate-distortion characteristics among the tested modes.
Rate-distortion analysis generally determines an amount of
distortion (or error) between an encoded block and an original,
unencoded block that was encoded to produce the encoded block, as
well as a bit rate (that is, a number of bits) used to produce the
encoded block. Intra-prediction module 46 may calculate ratios from
the distortions and rates for the various encoded blocks to
determine which intra-prediction mode exhibits the best
rate-distortion value for the block.
[0100] After predicting a current block, e.g., using
intra-prediction or inter-prediction, video encoder 20 may form a
residual video block by subtracting the prediction data calculated
by motion compensation unit 44 or intra-prediction module 46 from
the original video block being coded. Summer 50 represents the
component or components that may perform this subtraction
operation. Transform module 52 may apply a transform, such as a
discrete cosine transform (DCT) or a conceptually similar
transform, to the residual block, producing a video block
comprising residual transform coefficient values. Transform module
52 may perform other transforms, such as those defined by the H.264
standard, which are conceptually similar to DCT. Wavelet
transforms, integer transforms, sub-band transforms or other types
of transforms could also be used. In any case, transform module 52
may apply the transform to the residual block, producing a block of
residual transform coefficients. The transform may convert the
residual information from a pixel domain to a transform domain,
such as a frequency domain. Quantization unit 54 may quantize the
residual transform coefficients to further reduce bit rate. The
quantization process may reduce the bit depth associated with some
or all of the coefficients. The degree of quantization may be
modified by adjusting a quantization parameter.
[0101] Following quantization, entropy encoding unit 56 may entropy
encode the quantized transform coefficients, which may include
CAVLC, CABAC, PIPE, or another entropy coding technique. Following
the entropy coding by entropy encoding unit 56, the encoded video
may be transmitted to another device or archived for later
transmission or retrieval.
[0102] In some cases, entropy encoding unit 56 or another unit of
video encoder 20 may be configured to perform other coding
functions, in addition to entropy coding quantized transform
coefficients as described above. For example, entropy encoding unit
56 may construct header information for the block (e.g.,
macroblock, CU, or LCU), or video frame containing the block, with
appropriate syntax elements for transmission in the encoded video
bitstream. According to some coding standards, such syntax elements
may include scanning order information for the block, as previously
described. As also previously described, the scanning order
information may consume a high percentage of the overall compressed
video bitrate if coded inefficiently. As such, this disclosure
describes techniques that may enable coding the scanning order
information for the block more efficiently than when using other
methods.
[0103] In some examples, entropy encoding unit 56 of video encoder
20 may be configured to encode certain blocks of video data (e.g.,
one or more macroblocks, or TUs of a CU). In accordance with the
techniques of this disclosure, as one example, entropy encoding
unit 56 may be configured to encode information that identifies a
scanning order associated with the block, i.e., scanning order
information for the block. For example, entropy encoding unit 56
may be configured to determine a most probable scanning order for
the block, and encode an indication of whether the scanning order
associated with the block is the most probable scanning order. In
this example, each of the scanning order associated with the block
and the most probable scanning order may comprise one of a zig-zag
scanning order, a horizontal scanning order, and a vertical
scanning order. Again, the zig-zag, horizontal, and vertical
scanning orders are merely examples, and other scanning orders may
also be defined or used consistent with the techniques of this
disclosure.
[0104] To determine the most probable scanning order for the block,
entropy encoding unit 56 may be configured to determine a most
probable scanning order for the block based on a prediction mode
and a size associated with the block, as described in greater
detail below with reference to FIGS. 6A-6B. For example, entropy
encoding unit 56 may determine the most probable scanning order
using scanning order information for previously encoded blocks,
e.g., blocks with a same associated prediction mode and size as the
currently encoded block.
[0105] Furthermore, to encode the indication of whether the
scanning order associated with the block is the most probable
scanning order, entropy encoding unit 56 may be configured to
perform a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on at least
one context. For example, the at least one context may include one
of the most probable scanning order, a prediction mode associated
with the block, and a size associated with the block.
[0106] Additionally, the indication may comprise a single bit, or
"bin." For example, entropy encoding unit 56 may encode the bin to
indicate whether the scanning order is the most probable scanning
order (e.g., bin="0") or otherwise (e.g., bin="1").
[0107] In another example, to encode the scanning order information
for the block, entropy encoding unit 56 may be further configured
to, in the event the scanning order associated with the block is
not the most probable scanning order, encode an indication of the
scanning order associated with the block.
[0108] In this example, to encode the indication of the scanning
order associated with the block, entropy encoding unit 56 may be
configured to perform a context adaptive entropy coding process
(e.g., a CABAC process) that includes entropy encoding unit 56
applying a context model based on at least one context. For
example, the at least one context may include one of the most
probable scanning order, the prediction mode associated with the
block, and the size associated with the block.
[0109] Furthermore, the indication of the scanning order associated
with the block may also comprise a single bin. For example, entropy
encoding unit 56 may be configured to encode the bin to indicate
whether the scanning order is a first scanning order (e.g.,
bin="0") or a second scanning order (e.g., bin="1"). In this
example, the first and second scanning orders may comprise scanning
orders, other than the most probable scanning order, that are also
used to code blocks of video data within the corresponding coding
system 10 comprising video encoder 20 and video decoder 30. It
should be noted that, in other examples, the scanning order
associated with the block may comprise one of a greater number
(e.g., 3, 4, 5, . . . etc.) of scanning orders, other than the most
probable scanning order, that are also used to code blocks of video
data within system 10. As such, in other examples, entropy encoding
unit 56 may be configured to encode the indication of the scanning
order associated with the block using other techniques, e.g., using
multiple bins.
[0110] Accordingly, in this example, entropy encoding unit 56 may
be configured to encode the scanning order information for the
block by encoding the indication of whether the scanning order
associated with the block is the most probable scanning order, and,
in some cases, the indication of the scanning order associated with
the block.
[0111] The following is one example of computer code that may be
used to perform the techniques of this disclosure, consistent with
the example described above. For example, the computer code
includes an algorithm for configuring a two-dimensional array of
scanning order indices that correspond to most probable scanning
orders for blocks of video data. In this example, the most probable
scanning order for a particular block is determined based on an
intra-prediction mode and a size associated with the block.
Accordingly, each row of the two-dimensional array corresponds to a
size associated with a block of video data, and each column of the
array corresponds to an intra-prediction mode associated with the
block. In other words, each position within the two-dimensional
array indicates a most probable scanning order for a block of video
data being associated with a particular intra-prediction mode and
size. For example, the most probable scanning orders for the blocks
indicated by the two-dimensional array may be determined using
scanning order information corresponding to previously encoded
blocks.
[0112] In this example, the most probable scanning order for a
particular block is indicated using one of three scanning order
indices, i.e., "0," "1," and "2." As one example, the scanning
order indices may each represent one of a zig-zag scanning order, a
horizontal scanning order, and a vertical scanning order. In other
examples, the scanning order indices may represent other scanning
orders, and may comprise more or fewer indices.
[0113] The computer code also includes an encoding algorithm that
uses a most probable scanning order for a particular block
(determined based on an intra-prediction mode and a size associated
with the block using the two-dimensional array described above) to
encode scanning order information for the block. For example, the
algorithm encodes the scanning order information for the block
using between one and two bins, wherein each bin is encoded by
performing a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on contexts,
including the most probable scanning order, the intra-prediction
mode, and the size. As previously described, the contexts are used
to select probability estimates within the context model for
encoding a particular bin. Specifically, the probability estimates
indicate a likelihood of the bin having a given value (e.g., "0" or
"1").
TABLE-US-00001 const UChar mostProbableScan[4][34] = {{1, 2, 0, 0,
0, 1, 0, 2, 2, 0, 0, 1, 1, 0, 2, 2, 2, 2, 0, 1, 1, 1, 1, 1, 0, 0,
2, 2, 2, 2, 2, 2, 2, 2}, {1, 2, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 0,
0, 2, 2, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 0}, {1, 2,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 1, 0, 0,
0, 0, 0, 0, 0, 2, 2, 0, 0, 0}, {1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0}};
if ( scanIdx == mostProbableScan) {encodeBin( 1, context(
blockSize, mostProbableScan) );} else {encodeBin( 0, context(
blockSize, mostProbableScan) ); encodeBin( scanIdx >
mostProbableScan ? scanIdx-1:scanIdx, context( blockSize,
mostProbableScan+3));}
[0114] In another example, to encode the scanning order information
for the block, entropy encoding unit 56 may be further configured
to, in the event the scanning order associated with the block is
not the most probable scanning order, use a zig-zag scanning order
to encode the coefficients associated with the block. Accordingly,
in this example, after determining the most probable scanning order
for the block, and encoding the indication of whether the scanning
order associated with the block is the most probable scanning
order, entropy encoding unit 56 may be configured to not encode any
additional scanning order information for the block.
[0115] In still another example, to determine the most probable
scanning order for the block, entropy encoding unit 56 may be
configured to designate a zig-zag scanning order as the most
probable scanning order for the block. In this example, in a
similar manner as described above, to encode the scanning order
information for the block, entropy encoding unit 56 may be further
configured to, in the event the scanning order associated with the
block is not the most probable scanning order (i.e., in this
particular example, the zig-zag scanning order), encode an
indication of the scanning order associated with the block. In
other words, in this example, entropy encoding unit 56 may be
configured to presume the zig-zag scanning order to be the most
probable scanning order for the block, rather than perform an
actual determination of the most probable scanning order for the
block, e.g., using scanning order information for previously
encoded blocks.
[0116] In this example, to encode the indication of the scanning
order associated with the block, entropy encoding unit 56 may be
configured to perform a context adaptive entropy coding process
(e.g., a CABAC process) that includes entropy encoding unit 56
applying a context model based on at least one context. For
example, the at least one context may include one of the most
probable scanning order, the prediction mode associated with the
block, and the size associated with the block.
[0117] The indication of the scanning order associated with the
block may once again comprise a single bin. For example, entropy
encoding unit 56 may encode the bin to indicate whether the
scanning order is a first scanning order (e.g., bin="0") or a
second scanning order (e.g., bin="1"). In this example, the first
and second scanning orders may comprise scanning orders, other than
the most probable scanning order (i.e., in this particular example,
the zig-zag scanning order), that are also used to code blocks of
video data within system 10. It should be noted that, in other
examples, the scanning order associated with the block may comprise
one of a greater number (e.g., 3, 4, 5, . . . etc.) of scanning
orders, other than the most probable scanning order (i.e., in this
particular example, the zig-zag scanning order), that are also used
to code blocks of video data within system 10. As such, in other
examples, entropy encoding unit 56 may encode the indication of the
scanning order associated with the block using other techniques,
e.g., using multiple bins.
[0118] Accordingly, in this example, entropy encoding unit 56 may
be configured to encode the scanning order information for the
block by encoding the indication of whether the scanning order
associated with the block is the most probable scanning order,
(i.e., in this particular example, the zig-zag scanning order),
and, in some cases, the indication of the scanning order associated
with the block.
[0119] The following is another example of computer code used to
perform the techniques of this disclosure, consistent with the
example described above. For example, the computer code includes an
algorithm for configuring a two-dimensional array of context
indices for blocks of video data. In this example, each context
index for a particular block is determined based on an
intra-prediction mode and a size associated with the block.
Accordingly, each row of the two-dimensional array corresponds to a
size associated with a block of video data, and each column of the
array corresponds to an intra-prediction mode associated with the
block. In other words, each position within the two-dimensional
array includes a context index for a block of video data being
associated with a particular intra-prediction mode and size.
[0120] In this example, each context index for a particular block
comprises one of three indices, i.e., "0," "1," and "2." In other
examples, the context indices may comprise more or fewer
indices.
[0121] The computer code also includes an encoding algorithm that
uses a context index for a particular block (determined based on an
intra-prediction mode and a size associated with the block using
the two-dimensional array described above) to encode scanning order
information for the block. For example, the algorithm encodes the
scanning order information for the block using between one and two
bins, wherein each bin is encoded by performing a context adaptive
entropy coding process (e.g., a CABAC process) that includes
applying a context model based on contexts, including the context
index, the intra-prediction mode, and the size. As previously
described, the contexts are used to select probability estimates
within the context model for encoding a particular bin.
Specifically, the probability estimates indicate a likelihood of
the bin having a given value (e.g., "0" or "1").
TABLE-US-00002 const UChar scanContext [7][34] = { {0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {1,
2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, }, {1, 2, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0,
0, 0, }, {1, 2, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0,
0, 0, 1, 1, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 0, }, {1, 2, 0, 0, 0, 1,
0, 2, 2, 0, 0, 1, 1, 0, 2, 2, 2, 2, 0, 1, 1, 1, 1, 1, 0, 0, 2, 2,
2, 2, 2, 2, 2, 2, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, } }; if (
scanIdx == 0) {encodeBin( 0, context( blockSize, scanContext) ); }
else {encodeBin( 1, context( blockSize, scanContext) );
encodeBin(scanIdx > 1 ? 0:1, context( blockSize,
scanContext+3));}
[0122] To encode each bin (i.e., each bin used to represent the
indication of whether the scanning order associated with the block
is the most probable scanning order and the indication of the
scanning order associated with the block) using the context
adaptive entropy coding process described above, the corresponding
context model may include probability estimates that indicate a
probability of the bin comprising a given value (e.g., "0" or "1").
Entropy encoding unit 56 may use the probability estimates for the
bin to encode the bin by performing the context adaptive entropy
coding process. In some examples, entropy encoding unit 56 may
determine the probability estimates using values of corresponding
bins for previously encoded blocks of video data, e.g., blocks with
a same associated prediction mode and size as the currently encoded
block. In other examples, entropy encoding unit 56 also may update
the probability estimates using the value of the bin to reflect the
probability of the bin comprising a given value. For example,
entropy encoding unit 56 may use the updated probability estimates
to encode scanning order information for subsequently encoded
blocks of video data in the manner described above.
[0123] In this example, entropy encoding unit 56 may be further
configured to encode information that identifies a position of a
last significant coefficient within the block according to the
scanning order associated with the block, i.e., the last
significant coefficient position information for the block. For
example, the last significant coefficient position information for
the block may be represented using a sequence of last significant
coefficient flags, as previously described. Additionally, entropy
encoding unit 56 may be further configured to encode information
that identifies positions of all other significant coefficients
within the block, i.e., the significant coefficient position
information for the block. For example, the significant coefficient
position information for the block also may be represented using a
sequence of significant coefficient flags, as previously described.
As also previously described, entropy encoding unit 56 may encode
the last significant coefficient position information and the
significant coefficient position information by encoding each flag
of the respective sequence by performing a context adaptive entropy
coding process (e.g., a CABAC process) that includes applying a
context model based on a context. For example, the context may
include a position of the flag within the block according to the
scanning order associated with block.
[0124] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy encoding
unit 56 may determine the probability estimates using values of
corresponding last significant coefficient flags and significant
coefficient flags for previously encoded blocks of video data. In
other examples, entropy encoding unit 56 also may update the
probability estimates using the value of each flag to reflect the
probability of the flag comprising a given value. For example,
entropy encoding unit 56 may use the updated probability estimates
to encode last significant coefficient position information and
significant coefficient position information for subsequently
encoded blocks of video data in the manner described above. It
should be noted that, in other examples, entropy encoding unit 56
may encode the last significant coefficient position information
and the significant coefficient position information for the block
using other techniques.
[0125] In any case, after encoding the scanning order information,
and the last significant coefficient position information and the
significant coefficient position information, i.e., the SM data,
for the block in the manner described above, entropy encoding unit
56 may also encode the value of each significant coefficient (e.g.,
each significant coefficient's magnitude and sign, indicated by
syntax elements "coeff_abs_level_minus1" and "coeff_sign_flag,"
respectively) within the block.
[0126] Accordingly, the techniques of this disclosure may enable
entropy encoding unit 56 to encode scanning order information for
the block more efficiently than when using other methods. In this
manner, there may be a relative bit savings for a coded bitstream
including the scanning order information when using the techniques
of this disclosure.
[0127] Inverse quantization unit 58 and inverse transform module 60
apply inverse quantization and inverse transformation,
respectively, to reconstruct the residual block in the pixel
domain, e.g., for later use as a reference block. Motion
compensation unit 44 may calculate a reference block by adding the
residual block to a predictive block of one of the frames of memory
64. Motion compensation unit 44 may also apply one or more
interpolation filters to the reconstructed residual block to
calculate sub-integer pixel values for use in motion estimation.
Summer 62 adds the reconstructed residual block to the motion
compensated prediction block produced by motion compensation unit
44 to produce a reconstructed video block for storage in memory 64.
The reconstructed video block may be used by motion estimation unit
42 and motion compensation unit 44 as a reference block to
inter-code a block in a subsequent video frame.
[0128] In this manner, video encoder 20 represents an example of a
video coder configured to code information that identifies a
scanning order associated with a block of video data, wherein to
code the information that identifies the scanning order associated
with the block, the video coder is configured to determine a most
probable scanning order for the block, and code an indication of
whether the scanning order associated with the block is the most
probable scanning order.
[0129] FIG. 3 is a block diagram that illustrates an example of a
video decoder 30 that may implement techniques for using a most
probable scanning order to efficiently decode encoded scanning
order information for a block of video data, consistent with the
techniques of this disclosure. In the example of FIG. 3, video
decoder 30 includes an entropy decoding unit 70, motion
compensation unit 72, intra-prediction module 74, inverse
quantization unit 76, inverse transform module 78, memory 82 and
summer 80. Video decoder 30 may, in some examples, perform a
decoding pass generally reciprocal to the encoding pass described
with respect to video encoder 20 (FIG. 2). Motion compensation unit
72 may generate prediction data based on motion vectors received
from entropy decoding unit 70.
[0130] In some examples, video decoder 30 may be configured to
receive encoded video data (e.g., one or more macroblocks, or TUs
of a CU) from video encoder 20. In accordance with the techniques
of this disclosure, as one example, entropy decoding unit 70 may be
configured to decode information that identifies a scanning order
associated with the block, i.e., scanning order information for the
block. For example, entropy decoding unit 70 may be configured to
determine a most probable scanning order for the block, and decode
an indication of whether the scanning order associated with the
block is the most probable scanning order. In this example, each of
the scanning order associated with the block and the most probable
scanning order may comprise one of a zig-zag scanning order, a
horizontal scanning order, and a vertical scanning order. Again,
the zig-zag, horizontal, and vertical scanning orders are merely
examples, and other scanning orders may also be defined or used
consistent with the techniques of this disclosure.
[0131] To determine the most probable scanning order for the block,
entropy decoding unit 70 may be configured to determine a most
probable scanning order for the block based on a prediction mode
and a size associated with the block, as described in greater
detail below with reference to FIGS. 6A-6B.
[0132] Furthermore, to decode the indication of whether the
scanning order associated with the block is the most probable
scanning order, entropy decoding unit 70 may be configured to
perform a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on at least
one context. For example, the at least one context may include one
of the most probable scanning order, a prediction mode associated
with the block, and a size associated with the block.
[0133] Additionally, the indication may comprise a single bin. For
example, entropy decoding unit 70 may receive encoded scanning
order data, and decode the scanning order data to determine the bin
such that the bin indicates whether the scanning order is the most
probable scanning order (e.g., bin="0") or otherwise (e.g.,
bin="1").
[0134] In another example, to decode the scanning order information
for the block, entropy decoding unit 70 may be further configured
to, in the event the scanning order associated with the block is
not the most probable scanning order, decode an indication of the
scanning order associated with the block.
[0135] In this example, to decode the indication of the scanning
order associated with the block, entropy decoding unit 70 may be
configured to perform a context adaptive entropy coding process
(e.g., a CABAC process) that includes entropy decoding unit 70
applying a context model based on at least one context. For
example, the at least one context may include one of the most
probable scanning order, the prediction mode associated with the
block, and the size associated with the block.
[0136] Furthermore, the indication of the scanning order associated
with the block may also comprise a single bin. For example, entropy
decoding unit 70 may be configured to receive additional encoded
scanning order data, and decode the additional scanning order data
to determine the bin such that the bin indicates whether the
scanning order is a first scanning order (e.g., bin="0") or a
second scanning order (e.g., bin="1"). In this example, the first
and second scanning orders may comprise scanning orders, other than
the most probable scanning order, that are also used to code blocks
of video data within the corresponding coding system 10 comprising
video encoder 20 and video decoder 30. It should be noted that, in
other examples, the scanning order associated with the block may
comprise one of a greater number (e.g., 3, 4, 5, . . . etc.) of
scanning orders, other than the most probable scanning order, that
are also used to code blocks of video data within system 10. As
such, in other examples, entropy decoding unit 70 may be configured
to decode the indication of the scanning order associated with the
block using other techniques, e.g., decoding the additional
scanning order data to determine multiple bins.
[0137] Accordingly, in this example, entropy decoding unit 70 may
be configured to decode the scanning order information for the
block by decoding the indication of whether the scanning order
associated with the block is the most probable scanning order, and,
in some cases, the indication of the scanning order associated with
the block.
[0138] In another example, to decode the scanning order information
for the block, entropy decoding unit 70 may be further configured
to, in the event the scanning order associated with the block is
not the most probable scanning order, use a zig-zag scanning order
to decode the coefficients associated with the block. Accordingly,
in this example, after determining the most probable scanning order
for the block, and decoding the indication of whether the scanning
order associated with the block is the most probable scanning
order, entropy decoding unit 70 may be configured to not decode any
additional scanning order information for the block.
[0139] In still another example, to determine the most probable
scanning order for the block, entropy decoding unit 70 may be
configured to designate a zig-zag scanning order as the most
probable scanning order for the block. In this example, in a
similar manner as described above, to decode the scanning order
information for the block, entropy decoding unit 70 may be further
configured to, in the event the scanning order associated with the
block is not the most probable scanning order (i.e., in this
particular example, the zig-zag scanning order), decode an
indication of the scanning order associated with the block. In
other words, in this example, entropy decoding unit 70 may be
configured to presume the zig-zag scanning order to be the most
probable scanning order for the block, rather than perform an
actual determination of the most probable scanning order for the
block, e.g., using scanning order information for previously
decoded blocks.
[0140] In this example, to decode the indication of the scanning
order associated with the block, entropy decoding unit 70 may be
configured to perform a context adaptive entropy coding process
(e.g., a CABAC process) that includes entropy decoding unit 70
applying a context model based on at least one context. For
example, the at least one context may include one of the most
probable scanning order, the prediction mode associated with the
block, and the size associated with the block.
[0141] The indication of the scanning order associated with the
block may once again comprise a single bin. For example, entropy
decoding unit 70 may receive additional encoded scanning order
data, and decode the additional scanning order data to determine
the bin such that the bin indicates whether the scanning order is a
first scanning order (e.g., bin="0") or a second scanning order
(e.g., bin="1"). In this example, the first and second scanning
orders may comprise scanning orders, other than the most probable
scanning order (i.e., in this particular example, the zig-zag
scanning order), that are also used to code blocks of video data
within system 10. It should be noted that, in other examples, the
scanning order associated with the block may comprise one of a
greater number (e.g., 3, 4, 5, . . . etc.) of scanning orders,
other than the most probable scanning order (i.e., in this
particular example, the zig-zag scanning order), that are also used
to code blocks of video data within system 10. As such, in other
examples, entropy decoding unit 70 may decode the indication of the
scanning order associated with the block using other techniques,
e.g., decoding the additional scanning order data to determine
multiple bins.
[0142] Accordingly, in this example, entropy decoding unit 70 may
be configured to decode the scanning order information for the
block by decoding the indication of whether the scanning order
associated with the block is the most probable scanning order
(i.e., in this particular example, the zig-zag scanning order),
and, in some cases, the indication of the scanning order associated
with the block.
[0143] To decode each bin (i.e., each bin used to represent the
indication of whether the scanning order associated with the block
is the most probable scanning order and the indication of the
scanning order associated with the block) using the context
adaptive entropy coding process described above, the corresponding
context model may include probability estimates that indicate a
probability of the bin comprising a given value (e.g., "0" or "1").
Entropy decoding unit 70 may use the probability estimates for the
bin to decode the bin by performing the context adaptive entropy
coding process. In some examples, entropy decoding unit 70 may
determine the probability estimates using values of corresponding
bins for previously decoded blocks of video data, e.g., blocks with
a same associated prediction mode and size as the currently decoded
block. In other examples, entropy decoding unit 70 also may update
the probability estimates using the value of the bin to reflect the
probability of the bin comprising a given value. For example,
entropy decoding unit 70 may use the updated probability estimates
to decode scanning order information for subsequently decoded
blocks of video data in the manner described above.
[0144] In this example, entropy decoding unit 70 may be further
configured to decode information that identifies a position of a
last significant coefficient within the block according to the
scanning order associated with the block, i.e., the last
significant coefficient position information for the block. For
example, the last significant coefficient position information for
the block may be represented using a sequence of last significant
coefficient flags, as previously described. Additionally, entropy
decoding unit 70 may be further configured to decode information
that identifies positions of all other significant coefficients
within the block, i.e., the significant coefficient position
information for the block. For example, the significant coefficient
position information for the block also may be represented using a
sequence of significant coefficient flags, as previously described.
As also previously described, entropy decoding unit 70 may decode
the last significant coefficient position information and the
significant coefficient position information by decoding each flag
of the respective sequence by performing a context adaptive entropy
coding process (e.g., a CABAC process) that includes applying a
context model based on a context. For example, the context may
include a position of the flag within the block according to the
scanning order associated with block.
[0145] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy decoding
unit 70 may determine the probability estimates using values of
corresponding last significant coefficient flags and significant
coefficient flags for previously decoded blocks of video data. In
other examples, entropy decoding unit 70 also may update the
probability estimates using the value of each flag to reflect the
probability of the flag comprising a given value. For example,
entropy decoding unit 70 may use the updated probability estimates
to decode last significant coefficient position information and
significant coefficient position information for subsequently
decoded blocks of video data in the manner described above. It
should be noted that, in other examples, entropy decoding unit 70
may decode the last significant coefficient position information
and the significant coefficient position information for the block
using other techniques.
[0146] In any case, after decoding the scanning order information,
and the last significant coefficient position information and the
significant coefficient position information, i.e., the SM data,
for the block in the manner described above, entropy decoding unit
70 may also decode the value of each significant coefficient (e.g.,
each significant coefficient's magnitude and sign, indicated by
syntax elements "coeff_abs_level_minus1" and "coeff_sign_flag,"
respectively) within the block.
[0147] Accordingly, the techniques of this disclosure may enable
entropy decoding unit 70 to decode the scanning order information
for the block more efficiently than when using other methods. In
this manner, there may be a relative bit savings for a coded
bitstream including the scanning order information when using the
techniques of this disclosure.
[0148] Motion compensation unit 72 may use motion vectors received
in the bitstream to identify a prediction block in reference frames
in memory 82. Intra-prediction module 74 may use intra-prediction
modes received in the bitstream to form a prediction block from
spatially adjacent blocks.
[0149] Intra-prediction module 74 may use an indication of an
intra-prediction mode for the encoded block to intra-predict the
encoded block, e.g., using pixels of neighboring, previously
decoded blocks. For examples in which the block is inter-prediction
mode encoded, motion compensation unit 72 may receive information
defining a motion vector, in order to retrieve motion compensated
prediction data for the encoded block. In any case, motion
compensation unit 72 or intra-prediction module 74 may provide
information defining a prediction block to summer 80.
[0150] Inverse quantization unit 76 inverse quantizes, i.e.,
de-quantizes, the quantized block coefficients provided in the
bitstream and decoded by entropy decoding unit 70. The inverse
quantization process may include a conventional process, e.g., as
defined by the H.264 decoding standard or as performed by the HEVC
Test Model. The inverse quantization process may also include use
of a quantization parameter QP.sub.Y calculated by video encoder 20
for each block to determine a degree of quantization and, likewise,
a degree of inverse quantization that should be applied.
[0151] Inverse transform module 78 applies an inverse transform,
e.g., an inverse DCT, an inverse integer transform, or a
conceptually similar inverse transform process, to the transform
coefficients in order to produce residual blocks in the pixel
domain. Motion compensation unit 72 produces motion compensated
blocks, possibly performing interpolation based on interpolation
filters. Identifiers for interpolation filters to be used for
motion estimation with sub-pixel precision may be included in the
syntax elements. Motion compensation unit 72 may use interpolation
filters as used by video encoder 20 during encoding of the video
block to calculate interpolated values for sub-integer pixels of a
reference block. Motion compensation unit 72 may determine the
interpolation filters used by video encoder 20 according to
received syntax information and use the interpolation filters to
produce predictive blocks.
[0152] Motion compensation unit 72 uses some of the syntax
information for the encoded block to determine sizes of blocks used
to encode frame(s) of the encoded video sequence, partition
information that describes how each block of a frame or slice of
the encoded video sequence is partitioned, modes indicating how
each partition is encoded, one or more reference frames (and
reference frame lists) for each inter-encoded block or partition,
and other information to decode the encoded video sequence.
Intra-prediction module 74 may also use the syntax information for
the encoded block to intra-predict the encoded block, e.g., using
pixels of neighboring, previously decoded blocks, as described
above.
[0153] Summer 80 sums the residual blocks with the corresponding
prediction blocks generated by motion compensation unit 72 or
intra-prediction module 74 to form decoded blocks. If desired, a
deblocking filter may also be applied to filter the decoded blocks
in order to remove blockiness artifacts. The decoded video blocks
are then stored in memory 82, which provides reference blocks for
subsequent motion compensation and also produces decoded video for
presentation on a display device (such as display device 32 of FIG.
1).
[0154] In this manner, video decoder 30 represents an example of a
video coder configured to code information that identifies a
scanning order associated with a block of video data, wherein to
code the information that identifies the scanning order associated
with the block, the video coder is configured to determine a most
probable scanning order for the block, and code an indication of
whether the scanning order associated with the block is the most
probable scanning order.
[0155] FIGS. 4A-4C are conceptual diagrams that illustrate an
example of a block of video data and corresponding significant
coefficient position information and last significant coefficient
position information. As shown in FIG. 4A, a block of video data,
e.g., a macroblock, or a TU of a CU, may include quantized
transform coefficients. For example, as shown in FIG. 4A, block 400
may include quantized transform coefficients generated using
prediction, transform, and quantization techniques previously
described. Assume, for this example, that block 400 has a size of
2N.times.2N, wherein N equals to two. Accordingly, block 400 has a
size of 4.times.4, and includes sixteen quantized transform
coefficients, as also shown in FIG. 4A. Assume further, that the
scanning order associated with block 400 is the zig-zag scanning
order, as shown in FIG. 5A described in greater detail below.
[0156] In this example, a last significant coefficient within block
400 according to the zig-zag scanning order is a quantized
transform coefficient equal to "1," located in position 406 within
block 400. In other examples, as described above, a block may have
a size that is smaller or larger than the size of block 400, and
may include more or fewer quantized transform coefficients than
block 400. In still other examples, the scanning order associated
with block 400 may be a different scanning order, e.g., a
horizontal scanning order, a vertical scanning order, a diagonal
scanning order, or another scanning order.
[0157] FIG. 4B illustrates an example of significant coefficient
flag data, i.e., significant coefficient flags represented in map,
or block form, as previously described. In the example of FIG. 4B,
block 402 may correspond to block 400 depicted in FIG. 4A. In other
words, the significant coefficient flags of block 402 may
correspond to the quantized transform coefficients of block 400. As
shown in FIG. 4B, the significant coefficient flags of block 402
that are equal to "1" correspond to significant coefficients of
block 400. Similarly, the significant coefficient flags of block
402 that are equal to "0" correspond to zero, or non-significant
coefficients of block 400.
[0158] In this example, a significant coefficient flag of block 402
corresponding to the last significant coefficient within block 400
according to the zig-zag scanning order is a significant
coefficient flag equal to "1," located in position 408 within block
402. In other examples, the values of significant coefficient flags
used to indicate significant or non-significant coefficients may
vary (e.g., significant coefficient flags equal to "0" may
correspond to significant coefficients, and significant coefficient
flags equal to "1" may correspond to non-significant
coefficients).
[0159] FIG. 4C illustrates an example of last significant
coefficient flag data, i.e., last significant coefficient flags
represented in map, or block form, as also previously described. In
the example of FIG. 4C, block 404 may correspond to block 400 and
block 402 depicted in FIG. 4A and FIG. 4B, respectively. In other
words, the last significant coefficient flags of block 404 may
correspond to the quantized transform coefficients of block 400,
and to the significant coefficient flags of block 402.
[0160] As shown in FIG. 4C, the last significant coefficient flag
of block 404 that is equal to "1," located in position 410 within
block 404, corresponds to a last significant coefficient of block
400, and to a last one of the significant coefficient flags of
block 402 that are equal to "1," according to the zig-zag scanning
order. Similarly, the last significant coefficient flags of block
404 that are equal to "0" (i.e., all remaining last significant
coefficient flags) correspond to zero, or non-significant
coefficients of block 400, and to all significant coefficient flags
of block 402 that are equal to "1" other than the last one of such
significant coefficient flags according to the zig-zag scanning
order.
[0161] The values of the last significant coefficient flags used to
indicate a last significant coefficient according to a scanning
order may vary (e.g., a last significant coefficient flag equal to
"0" may correspond to a last significant coefficient according to
the scanning order, and last significant coefficient flags equal to
"1" may correspond to all remaining coefficients). In any case, the
significant coefficient flags of block 402, and the last
significant coefficient flags of block 404, may be collectively
referred to as SM data for block 400.
[0162] As described above, significant coefficient position
information for a block of video data may be indicated by
serializing significant coefficient flags for the block from a
two-dimensional block representation, as depicted in block 402
shown in FIG. 4B, into a one-dimensional array, using a scanning
order associated with the block. In the example of blocks 400-402
shown in FIGS. 4A-4B, again assuming the zig-zag scanning order,
the significant coefficient position information for block 400 may
be indicated by serializing the significant coefficient flags of
block 402 into a one-dimensional array. That is, the significant
coefficient position information for block 400 may be indicated by
generating a sequence of significant coefficient flags of block 402
according to the zig-zag scanning order.
[0163] In this example, the generated sequence may correspond to a
value "111111," representing the first 6 significant coefficient
flags of block 402 according to the zig-zag scanning order. It
should be noted that the generated sequence may contain significant
coefficient flags corresponding to a range of block positions
within block 400, starting from a first block position in the
zig-zag scanning order (i.e., the DC position) and ending with a
block position corresponding to the last significant coefficient of
block 400 according to the zig-zag scanning order (i.e.,
corresponding to the last significant coefficient flag equal to "1"
of block 404).
[0164] As also described above, last significant coefficient
position information for the block may be indicated by serializing
last significant coefficient flags for the block from a
two-dimensional block representation, as depicted in block 404
shown in FIG. 4C, into a one-dimensional array, using a scanning
order associated with the block. In the example of blocks 400-404
shown in FIGS. 4A-4C, again assuming the zig-zag scanning order,
the last significant coefficient position information for block 400
may be indicated by serializing the last significant coefficient
flags of block 404 into a one-dimensional array. That is, the last
significant coefficient position information for block 400 may be
indicated by generating a sequence of last significant coefficient
flags of block 404 according to the zig-zag scanning order. In this
example, the generated sequence may correspond to a value "000001,"
representing the first 6 last significant coefficient flags of
block 404 according to the zig-zag scanning order.
[0165] Once again, it should be noted that the generated sequence
may contain last significant coefficient flags corresponding to a
range of block positions within block 400, starting from the first
block position in the zig-zag scanning order, and ending with the
block position corresponding to the last significant coefficient of
block 400 according to the zig-zag scanning order (i.e.,
corresponding to the last significant coefficient flag equal to "1"
of block 404). Accordingly, in this example, no last significant
coefficient flags following the last significant coefficient flag
equal to "1" according to the zig-zag scanning order are included
in the sequence. Generally speaking, last significant coefficient
flags following a last significant coefficient flag equal to "1"
according to a scanning order associated with a block of video data
may not be needed to indicate last significant coefficient position
information for the block. As such, in some examples, these flags
are omitted from the generated sequence of last significant
coefficient flags used to indicate the information.
[0166] It should also be noted that, as described above, if the
last significant coefficient is located within a last block
position according to the scanning order (e.g., the bottom right
block position), the generated sequence may not include a last
significant coefficient flag corresponding to the last block
position, because the position may be inferred to contain the last
significant coefficient for the block. Accordingly, in this
example, the generated sequence may correspond to a value
"000000000000000," wherein the last significant coefficient flag
corresponding to the last block position is not included in the
sequence, and is inferred to equal "1."
[0167] FIGS. 5A-5C are conceptual diagrams that illustrate examples
of blocks of video data scanned using a zig-zag scanning order, a
horizontal scanning order, and a vertical scanning order,
respectively. As shown in FIGS. 5A-5C, an 8.times.8 block of video
data, e.g., a macroblock, or a TU of a CU, may include sixty-four
quantized transform coefficients in corresponding block positions,
denoted with circles. For example, blocks 500-504 may each include
sixty-four quantized transform coefficients generated using
prediction, transform, and quantization techniques previously
described, again, wherein each corresponding block position is
denoted with a circle. Assume, for this example, that blocks
500-504 have a size of 2N.times.2N, wherein N equals to four.
Accordingly, blocks 500-504 have a size of 8.times.8.
[0168] As shown in FIG. 5A, the scanning order associated with
block 500 is the zig-zag scanning order. The zig-zag scanning order
scans the quantized transform coefficients of block 500 in a
diagonal manner as indicated by the arrows in FIG. 5A. Similarly,
as shown in FIGS. 5B and 5C, the scanning orders associated with
blocks 502 and 504 are the horizontal scanning order and the
vertical scanning order, respectively. The horizontal scanning
order scans the quantized transform coefficients of block 502 in a
horizontal line-by-line, or "raster" manner, while the vertical
scanning order scans the quantized transform coefficients of block
504 in a vertical line-by-line, or "rotated raster" manner, also as
indicated by the arrows in FIGS. 5B and 5C.
[0169] In other examples, as described above, a block may have a
size that is smaller or larger than the size of blocks 500-504, and
may include more or fewer quantized transform coefficients and
corresponding block positions. In these examples, a scanning order
associated with the block may scan the quantized transform
coefficients of the block in a substantially similar manner as
shown in the examples of the 8.times.8 blocks 500-504 of FIGS.
5A-5C, e.g., a 4.times.4 block, or a 16.times.16 block, may be
scanned following any of the scanning orders previously
described.
[0170] As previously described, the techniques of this disclose may
also apply with respect to a wide variety of other scanning orders,
including a diagonal scanning order, scanning orders that are
combinations of zigzag, horizontal, vertical, and/or diagonal
scanning orders, as well as scanning orders that are partially
zigzag, partially horizontal, partially vertical, and/or partially
diagonal.
[0171] FIGS. 6A-6B are conceptual diagrams that illustrate examples
of blocks video data having various sizes, and examples of blocks
of video data for which various prediction modes are used to
generate prediction data, consistent with the techniques of this
disclosure. As shown in FIG. 6A, block 600, e.g., a macroblock, or
a TU of a CU of video data, may have a particular size. Assume for
this example that the size of block 600 is 2N.times.2N, where N
equals to thirty-two. Accordingly, block 600 has a size of
64.times.64. Assume further that block 600 is recursively
partitioned, or split, into smaller blocks, including blocks
602-608 also shown in FIG. 6A, as previously described with
reference to FIG. 1. Assume, for example, that block 602 has a size
of 32.times.32, block 604 has a size of 16.times.16, block 606 has
a size of 8.times.8, and block 608 has a size of 4.times.4. In
other examples, block 600 may be partitioned into more or fewer
smaller blocks than blocks 602-608. In still other examples, block
600 and any partitions thereof may have different sizes than the
sizes of blocks 600-608.
[0172] As shown in FIG. 6B, blocks 610A-610I may each be coded
using one of a variety of prediction modes. The different
illustrations of FIG. 6B show different directional prediction
modes, in which prediction data may be obtained or derived from
neighboring pixel data according to the directional arrows shown in
the different illustrations. Other intra-prediction modes, such as
a DC mode, a planar mode, or other directional prediction modes,
may also be used. In some cases, thirty-three different
intra-prediction modes may be supported. In any case, as shown in
FIG. 6B, each of blocks 610A-610I may be coded using a unique
intra-prediction mode, as illustrated for each of blocks 610A-610I,
wherein pixels of neighboring blocks of video data are used to
predict pixels of the respective block. In other examples, blocks
610A-610I may be coded using other prediction modes not shown in
FIG. 6B.
[0173] As such, in accordance with the techniques of this
disclosure, at least one of the block sizes associated with blocks
600-608 depicted in FIG. 6A, and the prediction modes associated
with blocks 610A-610I depicted in FIG. 6B, may each be used as a
context when performing a context adaptive entropy coding process
(e.g., a CABAC process) to code scanning order information for a
particular one of blocks 600-608 and 610A-610I, as previously
described.
[0174] FIG. 7 is a flowchart that illustrates an example method for
using a most probable scanning order to efficiently code scanning
order information for a block of video data consistent with the
techniques of this disclosure. The techniques of FIG. 7 may
generally be performed by any processing unit or processor, whether
implemented in hardware, software, firmware, or a combination
thereof, and when implemented in software or firmware,
corresponding hardware may be provided to execute instructions for
the software or firmware. For purposes of example, the techniques
of FIG. 7 are described with respect to video encoder 20 (FIGS. 1
and 2) and/or video decoder 30 (FIGS. 1 and 3), although it should
be understood that other devices may be configured to perform
similar techniques. Moreover, the steps illustrated in FIG. 7 may
be performed in a different order or in parallel, and additional
steps may be added and certain steps omitted, without departing
from the techniques of this disclosure.
[0175] Initially, in some examples, video encoder 20 and/or video
decoder 30 may code information that indicates a position of a last
significant coefficient within a block of video data according to a
scanning order associated with the block (700), i.e., the last
significant coefficient position information for the block. For
example, the block may be a macroblock, or a TU of a CU, as
previously described. Furthermore, the scanning order associated
with the block may comprise one of a zig-zag scanning order, a
horizontal scanning order, and a vertical scanning order. In this
manner, the example method of FIG. 7 may be applicable to any
coding system that uses a plurality of scanning orders to code
blocks of video data.
[0176] In some examples, the last significant coefficient position
information for the block may be represented using a sequence of
last significant coefficient flags, as previously described. As
also previously described, video encoder 20 and/or video decoder 30
may code the last significant coefficient position information by
coding each last significant coefficient flag of the sequence by
performing a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on a context.
For example, the context may include a position of the flag within
the block according to the scanning order associated with
block.
[0177] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, video encoder 20
and/or video decoder 30 may determine the probability estimates
using values of corresponding last significant coefficient flags
for previously coded blocks of video data. In other examples, video
encoder 20 and/or video decoder 30 also may update the probability
estimates using the value of each flag to reflect the probability
of the flag comprising a given value. For example, video encoder 20
and/or video decoder 30 may use the updated probability estimates
to code last significant coefficient position information for
subsequently coded blocks of video data in the manner described
above. It should be noted that, in other examples, video encoder 20
and/or video decoder 30 may code the last significant coefficient
position information for the block using other techniques.
[0178] Video encoder 20 and/or video decoder 30 may further
determine a most probable scanning order for the block (702). For
example, to determine the most probable scanning order for the
block, video encoder 20 and/or video decoder 30 may determine a
most probable scanning order for the block based on a prediction
mode and a size associated with the block, as previously described
with reference to FIGS. 6A-6B. As one example, video encoder 20
and/or video decoder 30 may make this determination using scanning
order information for previously coded blocks, e.g., blocks with a
same associated prediction mode and size as the currently coded
block. The most probable scanning order may also comprise one of a
zig-zag scanning order, a horizontal scanning order, and a vertical
scanning order.
[0179] Video encoder 20 and/or video decoder 30 may further code an
indication of whether the scanning order associated with the block
is the most probable scanning order (704). For example, video
encoder 20 may encode the indication, as described in greater
detail in the example method of FIG. 8, and video decoder 30 may
decode the indication, as described in greater detail in the
example method of FIG. 9. Video encoder 20 and/or video decoder 30
may code the indication by performing a context adaptive entropy
coding process (e.g., a CABAC process) that includes applying a
context model based on at least one context. For example, the at
least one context may include one of the most probable scanning
order, the prediction mode associated with the block, and the size
associated with the block. The indication may comprise a single
bit, or "bin." For example, video encoder 20 and/or video decoder
30 may code the bin to indicate whether the scanning order is the
most probable scanning order (e.g., bin="0") or otherwise (e.g.,
bin="1").
[0180] In the event the scanning order associated with the block is
the most probable scanning order (706), video encoder 20 and/or
video decoder 30 may stop coding the information that identifies
the scanning order associated with the block (710), i.e., the
scanning order information for the block. For example, video
encoder 20 and/or video decoder 30 may proceed to other coding
tasks, e.g., coding of other syntax elements for the block, or a
subsequent block, as described above.
[0181] In the event the scanning order associated with the block is
not the most probable scanning order (706), however, video encoder
20 and/or video decoder 30 may further code an indication of the
scanning order associated with the block (708). Once again, video
encoder 20 and/or video decoder 30 may code the indication by
performing a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on at least
one context. For example, the at least one context may include one
of the most probable scanning order, the prediction mode associated
with the block, and the size associated with the block. The
indication of the scanning order associated with the block may also
comprise a single bin. For example, video encoder 20 and/or video
decoder 30 may code the bin to indicate whether the scanning order
is a first scanning order (e.g., bin="0") or a second scanning
order (e.g., bin="1"). In this example, the first and second
scanning orders may comprise scanning orders, other than the most
probable scanning order, that are also used to code blocks of video
data within the corresponding coding system 10 comprising video
encoder 20 and video decoder 30. It should be noted that, in other
examples, the scanning order associated with the block may comprise
one of a greater number (e.g., 3, 4, 5, . . . etc.) of scanning
orders, other than the most probable scanning order, that are also
used to code blocks of video data within system 10. As such, in
other examples, video encoder 20 and/or video decoder 30 may code
the indication of the scanning order associated with the block
using other techniques, e.g., using multiple bins.
[0182] To code each bin (i.e., each bin used to represent the
indication of whether the scanning order associated with the block
is the most probable scanning order and the indication of the
scanning order associated with the block) using the context
adaptive entropy coding process described above, the corresponding
context model may include probability estimates that indicate a
probability of the bin comprising a given value (e.g., "0" or "1").
Video encoder 20 and/or video decoder 30 may use the probability
estimates for the bin to code the bin by performing the context
adaptive entropy coding process. In some examples, video encoder 20
and/or video decoder 30 may determine the probability estimates
using values of corresponding bins for previously coded blocks of
video data, e.g., blocks with a same associated prediction mode and
size as the currently coded block. In other examples, video encoder
20 and/or video decoder 30 also may update the probability
estimates using the value of the bin to reflect the probability of
the bin comprising a given value. For example, video encoder 20
and/or video decoder 30 may use the updated probability estimates
to code scanning order information for subsequently coded blocks of
video data in the manner described above.
[0183] In any case, after coding the indication of the scanning
order associated with the block (708), video encoder 20 and/or
video decoder 30 may stop coding the information that identifies
the scanning order associated with the block (710), i.e., the
scanning order information for the block. Once again, for example,
video encoder 20 and/or video decoder 30 may proceed to other
coding tasks, e.g., coding of other syntax elements for the block,
or a subsequent block, as described above.
[0184] In some examples, video encoder 20 and/or video decoder 30
may further code information that indicates positions of all other
significant coefficients within the block (712), i.e., the
significant coefficient position information for the block. For
example, the significant coefficient position information for the
block may be represented using a sequence of significant
coefficient flags, as previously described. As also previously
described, video encoder 20 and/or video decoder 30 may code the
significant coefficient position information by coding each
significant coefficient flag of the sequence by performing a
context adaptive entropy coding process (e.g., a CABAC process)
that includes applying a context model based on a context. For
example, the context may include a position of the flag within the
block according to the scanning order associated with block.
[0185] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, video encoder 20
and/or video decoder 30 may determine the probability estimates
using values of corresponding significant coefficient flags for
previously coded blocks of video data. In other examples, video
encoder 20 and/or video decoder 30 also may update the probability
estimates using the value of each flag to reflect the probability
of the flag comprising a given value. For example, video encoder 20
and/or video decoder 30 may use the updated probability estimates
to code significant coefficient position information for
subsequently coded blocks of video data in the manner described
above. It should be noted that, in other examples, video encoder 20
and/or video decoder 30 may code the significant coefficient
position information for the block using other techniques.
[0186] In this manner, the method of FIG. 7 represents an example
of a method of coding information that identifies a scanning order
associated with a block of video data, including determining a most
probable scanning order for the block, and coding an indication of
whether the scanning order associated with the block is the most
probable scanning order.
[0187] FIG. 8 is a flowchart that illustrates an example method for
using a most probable scanning order to efficiently encode scanning
order information for a block of video data consistent with the
techniques of this disclosure. The techniques of FIG. 8 may
generally be performed by any processing unit or processor, whether
implemented in hardware, software, firmware, or a combination
thereof, and when implemented in software or firmware,
corresponding hardware may be provided to execute instructions for
the software or firmware. For purposes of example, the techniques
of FIG. 8 are described with respect to entropy encoding unit 56
(FIG. 2), although it should be understood that other devices may
be configured to perform similar techniques. Moreover, the steps
illustrated in FIG. 8 may be performed in a different order or in
parallel, and additional steps may be added and certain steps
omitted, without departing from the techniques of this
disclosure.
[0188] Initially, entropy encoding unit 56 may receive a block of
video data (800). For example, the block may be a macroblock, or a
TU of a CU, as previously described. In some examples, entropy
encoding unit 56 may further encode information that indicates a
position of a last significant coefficient within the block
according to a scanning order associated with the block (802),
i.e., the last significant coefficient position information for the
block. For example, the scanning order associated with the block
may comprise one of a zig-zag scanning order, a horizontal scanning
order, and a vertical scanning order. In this manner, the example
method of FIG. 8 may be applicable to any coding system that uses a
plurality of scanning orders to code blocks of video data.
[0189] In some examples, the last significant coefficient position
information for the block may be represented using a sequence of
last significant coefficient flags, as previously described. As
also previously described, entropy encoding unit 56 may encode the
last significant coefficient position information by encoding each
last significant coefficient flag of the sequence by performing a
context adaptive entropy coding process (e.g., a CABAC process)
that includes applying a context model based on a context. For
example, the context may include a position of the flag within the
block according to the scanning order associated with block.
[0190] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy encoding
unit 56 may determine the probability estimates using values of
corresponding last significant coefficient flags for previously
encoded blocks of video data. In other examples, entropy encoding
unit 56 also may update the probability estimates using the value
of each flag to reflect the probability of the flag comprising a
given value. For example, entropy encoding unit 56 may use the
updated probability estimates to encode last significant
coefficient position information for subsequently encoded blocks of
video data in the manner described above. It should be noted that,
in other examples, entropy encoding unit 56 may encode the last
significant coefficient position information for the block using
other techniques.
[0191] Entropy encoding unit 56 may further determine a most
probable scanning order for the block (804). For example, to
determine the most probable scanning order for the block, entropy
encoding unit 56 may determine a most probable scanning order for
the block based on a prediction mode and a size associated with the
block, as previously described with reference to FIGS. 6A-6B. As
one example, entropy encoding unit 56 may make this determination
using scanning order information for previously encoded blocks,
e.g., blocks with a same associated prediction mode and size as the
currently encoded block. The most probable scanning order may also
comprise one of a zig-zag scanning order, a horizontal scanning
order, and a vertical scanning order.
[0192] Entropy encoding unit 56 may further encode an indication of
whether the scanning order associated with the block is the most
probable scanning order (806). Entropy encoding unit 56 may encode
the indication by performing a context adaptive entropy coding
process (e.g., a CABAC process) that includes applying a context
model based on at least one context. For example, the at least one
context may include one of the most probable scanning order, the
prediction mode associated with the block, and the size associated
with the block. The indication may comprise a single bin. For
example, entropy encoding unit 56 may encode the bin to indicate
whether the scanning order is the most probable scanning order
(e.g., bin="0") or otherwise (e.g., bin="1").
[0193] In the event the scanning order associated with the block is
the most probable scanning order (808), entropy encoding unit 56
may stop encoding the information that identifies the scanning
order associated with the block (816), i.e., the scanning order
information for the block. For example, entropy encoding unit 56
may proceed to other coding tasks, e.g., encoding of other syntax
elements for the block, or a subsequent block, as described
above.
[0194] In the event the scanning order associated with the block is
not the most probable scanning order (808), however, entropy
encoding unit 56 may further encode an indication of the scanning
order associated with the block (810). Once again, entropy encoding
unit 56 may code the indication by performing a context adaptive
entropy coding process (e.g., a CABAC process) that includes
applying a context model based on at least one context. For
example, the at least one context may include one of the most
probable scanning order, the prediction mode associated with the
block, and the size associated with the block. The indication of
the scanning order associated with the block may also comprise a
single bin. For example, entropy encoding unit 56 may encode the
bin to indicate whether the scanning order is a first scanning
order (e.g., bin="0") or a second scanning order (e.g., bin="1"),
wherein the first and second scanning orders comprise scanning
orders, other than the most probable scanning order, that are also
used to code blocks of video data within the corresponding coding
system 10 comprising video encoder 20 and video decoder 30. It
should be noted that, in other examples, the scanning order
associated with the block may comprise one of a greater number
(e.g., 3, 4, 5, . . . etc.) of scanning orders, other than the most
probable scanning order, that are also used to code blocks of video
data within system 10. As such, in other examples, entropy encoding
unit 56 may encode the indication of the scanning order associated
with the block using other techniques, e.g., using multiple
bins.
[0195] To encode each bin (i.e., each bin used to represent the
indication of whether the scanning order associated with the block
is the most probable scanning order and the indication of the
scanning order associated with the block) using the context
adaptive entropy coding process described above, the corresponding
context model may include probability estimates that indicate a
probability of the bin comprising a given value (e.g., "0" or "1").
Entropy encoding unit 56 may use the probability estimates for the
bin to encode the bin by performing the context adaptive entropy
coding process. In some examples, entropy encoding unit 56 may
determine the probability estimates using values of corresponding
bins for previously encoded blocks of video data, e.g., blocks with
a same associated prediction mode and size as the currently coded
block. In other examples, entropy encoding unit 56 also may update
the probability estimates using the value of the bin to reflect the
probability of the bin comprising a given value. For example,
entropy encoding unit 56 may use the updated probability estimates
to encode scanning order information for subsequently encoded
blocks of video data in the manner described above.
[0196] In any case, after encoding the indication of the scanning
order associated with the block (810), entropy encoding unit 56 may
stop encoding the information that identifies the scanning order
associated with the block (812), i.e., the scanning order
information for the block. Once again, for example, entropy
encoding unit 56 may proceed to other coding tasks, e.g., encoding
of other syntax elements for the block, or a subsequent block, as
described above.
[0197] In some examples, entropy encoding unit 56 may further
encode information that indicates positions of all other
significant coefficients within the block (814), i.e., the
significant coefficient position information for the block. For
example, the significant coefficient position information for the
block may be represented using a sequence of significant
coefficient flags, as previously described. As also previously
described, entropy encoding unit 56 may encode the significant
coefficient position information by encoding each significant
coefficient flag of the sequence by performing a context adaptive
entropy coding process (e.g., a CABAC process) that includes
applying a context model based on a context. For example, the
context may include a position of the flag within the block
according to the scanning order associated with block.
[0198] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy encoding
unit 56 may determine the probability estimates using values of
corresponding significant coefficient flags for previously encoded
blocks of video data. In other examples, entropy encoding unit 56
also may update the probability estimates using the value of each
flag to reflect the probability of the flag comprising a given
value. For example, entropy encoding unit 56 may use the updated
probability estimates to encode significant coefficient position
information for subsequently encoded blocks of video data in the
manner described above. It should be noted that, in other examples,
entropy encoding unit 56 may encode the significant coefficient
position information for the block using other techniques.
[0199] Finally, entropy encoding unit 56 may stop encoding the
block (816). For example, entropy encoding unit 56 may proceed to
other coding tasks, e.g., encoding subsequent blocks, as described
above.
[0200] In this manner, the method of FIG. 8 represents an example
of a method of encoding information that identifies a scanning
order associated with a block of video data, including determining
a most probable scanning order for the block, and coding an
indication of whether the scanning order associated with the block
is the most probable scanning order.
[0201] FIG. 9 is a flowchart that illustrates an example method for
using a most probable scanning order to efficiently decode encoded
scanning order information for a block of video data consistent
with the techniques of this disclosure. The techniques of FIG. 9
may generally be performed by any processing unit or processor,
whether implemented in hardware, software, firmware, or a
combination thereof, and when implemented in software or firmware,
corresponding hardware may be provided to execute instructions for
the software or firmware. For purposes of example, the techniques
of FIG. 9 are described with respect to entropy decoding unit 70
(FIG. 3), although it should be understood that other devices may
be configured to perform similar techniques. Moreover, the steps
illustrated in FIG. 9 may be performed in a different order or in
parallel, and additional steps may be added and certain steps
omitted, without departing from the techniques of this
disclosure.
[0202] Initially, entropy decoding unit 70 may receive encoded
significance data for a block of video data (900). For example, the
block may be a macroblock, or a TU of a CU, as previously
described. Entropy decoding unit 70 may further decode the
significance data to determine information that indicates a
position of a last significant coefficient within the block
according to a scanning order associated with the block (902),
i.e., the last significant coefficient position information for the
block. For example, the scanning order associated with the block
may comprise one of a zig-zag scanning order, a horizontal scanning
order, and a vertical scanning order. In this manner, the example
method of FIG. 9 may be applicable to any coding system that uses a
plurality of scanning orders to code blocks of video data.
[0203] In some examples, the last significant coefficient position
information for the block may be represented using a sequence of
last significant coefficient flags, as previously described. As
also previously described, entropy decoding unit 70 may decode the
significance data to determine the last significant coefficient
position information by decoding the significance data to generate
each last significant coefficient flag of the sequence. For
example, entropy decoding unit 70 may perform a context adaptive
entropy coding process (e.g., a CABAC process) that includes
applying a context model based on a context, wherein the context
may include a position of the flag within the block according to
the scanning order associated with block.
[0204] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy decoding
unit 70 may determine the probability estimates using values of
corresponding last significant coefficient flags for previously
decoded blocks of video data. In other examples, entropy decoding
unit 70 also may update the probability estimates using the value
of each flag to reflect the probability of the flag comprising a
given value. For example, entropy decoding unit 70 may use the
updated probability estimates to decode last significant
coefficient position information for subsequently decoded blocks of
video data in the manner described above. It should be noted that,
in other examples, entropy decoding unit 70 may decode the last
significant coefficient position information for the block using
other techniques.
[0205] Entropy decoding unit 70 may further determine a most
probable scanning order for the block (904). For example, to
determine the most probable scanning order for the block, entropy
decoding unit 70 may determine a most probable scanning order for
the block based on a prediction mode and a size associated with the
block, as previously described with reference to FIGS. 6A-6B. As
one example, entropy decoding unit 70 may make this determination
using scanning order information for previously decoded blocks,
e.g., blocks with a same associated prediction mode and size as the
currently decoded block. The most probable scanning order may also
comprise one of a zig-zag scanning order, a horizontal scanning
order, and a vertical scanning order.
[0206] Entropy decoding unit 70 may further receive encoded
scanning order data for the block (906). Entropy decoding unit 70
may further decode the scanning order data to determine an
indication of whether the scanning order associated with the block
is the most probable scanning order (908). Entropy decoding unit 70
may decode the scanning order data to determine the indication by
performing a context adaptive entropy coding process (e.g., a CABAC
process) that includes applying a context model based on at least
one context. For example, the at least one context may include one
of the most probable scanning order, the prediction mode associated
with the block, and the size associated with the block. The
indication may comprise a single bin. For example, entropy decoding
unit 70 may decode the scanning order data to determine the bin,
such that the bin indicates whether the scanning order is the most
probable scanning order (e.g., bin="0") or otherwise (e.g.,
bin="1").
[0207] In the event the scanning order associated with the block is
the most probable scanning order (910), entropy decoding unit 70
may stop decoding the information that identifies the scanning
order associated with the block (916), i.e., the scanning order
information for the block. For example, entropy decoding unit 70
may proceed to other coding tasks, e.g., decoding of other syntax
elements for the block, or a subsequent block, as described
above.
[0208] In the event the scanning order associated with the block is
not the most probable scanning order (910), however, entropy
decoding unit 70 may further receive additional encoded scanning
order data for the block (912). Entropy decoding unit 70 may
further decode the additional scanning order data to determine an
indication of the scanning order associated with the block (914).
Once again, entropy decoding unit 70 may decode the additional
scanning order data to determine the indication by performing a
context adaptive entropy coding process (e.g., a CABAC process)
that includes applying a context model based on at least one
context. For example, the at least one context may include one of
the most probable scanning order, the prediction mode associated
with the block, and the size associated with the block. The
indication of the scanning order associated with the block may also
comprise a single bin. For example, entropy decoding unit 70 may
decode the additional scanning order data to determine the bin,
such that the bin indicates whether the scanning order is a first
scanning order (e.g., bin="0") or a second scanning order (e.g.,
bin="1"). In this example, the first and second scanning orders may
comprise scanning orders, other than the most probable scanning
order, that are also used to code blocks of video data within the
corresponding coding system 10 comprising video encoder 20 and
video decoder 30. It should be noted that, in other examples, the
scanning order associated with the block may comprise one of a
greater number (e.g., 3, 4, 5, . . . etc.) of scanning orders,
other than the most probable scanning order, that are also used to
code blocks of video data within system 10. As such, in other
examples, entropy decoding unit 70 may decode the additional
scanning order data to determine the indication of the scanning
order associated with the block using other techniques, e.g., using
multiple bins.
[0209] To determine each bin (i.e., each bin used to represent the
indication of whether the scanning order associated with the block
is the most probable scanning order and the indication of the
scanning order associated with the block) using the context
adaptive entropy coding process described above, the corresponding
context model may include probability estimates that indicate a
probability of the bin comprising a given value (e.g., "0" or "1").
Entropy decoding unit 70 may use the probability estimates for the
bin to determine the bin by performing the context adaptive entropy
coding process. In some examples, entropy decoding unit 70 may
determine the probability estimates using values of corresponding
bins for previously decoded blocks of video data, e.g., blocks with
a same associated prediction mode and size as the currently coded
block. In other examples, entropy decoding unit 70 also may update
the probability estimates using the value of the bin to reflect the
probability of the bin comprising a given value. For example,
entropy decoding unit 70 may use the updated probability estimates
to decode scanning order information for subsequently decoded
blocks of video data in the manner described above.
[0210] In any case, after decoding the additional scanning order
data to determine the indication of the scanning order associated
with the block (914), entropy decoding unit 70 may stop decoding
the information that identifies the scanning order associated with
the block (916), i.e., the scanning order information for the
block. Once again, for example, entropy decoding unit 70 may
proceed to other coding tasks, e.g., decoding of other syntax
elements for the block, or a subsequent block, as described
above.
[0211] In some examples, entropy decoding unit 70 may further
receive remaining encoded significance data for the block (918).
Entropy decoding unit 70 may further decode the remaining
significance data to determine information that indicates positions
of all other significant coefficients within the block (920), i.e.,
the significant coefficient position information for the block. For
example, the significant coefficient position information for the
block may be represented using a sequence of significant
coefficient flags, as previously described. As also previously
described, entropy decoding unit 70 may decode the remaining
significance data to determine the significant coefficient position
information by decoding the remaining significance data to generate
each significant coefficient flag of the sequence. For example,
entropy decoding unit 70 may perform a context adaptive entropy
coding process (e.g., a CABAC process) that includes applying a
context model based on a context, wherein the context may include a
position of the flag within the block according to the scanning
order associated with block.
[0212] In these examples, the context model may include probability
estimates that indicate a probability of each flag comprising a
given value (e.g., "0" or "1"). In some examples, entropy decoding
unit 70 may determine the probability estimates using values of
corresponding significant coefficient flags for previously decoded
blocks of video data. In other examples, entropy decoding unit 70
also may update the probability estimates using the value of each
flag to reflect the probability of the flag comprising a given
value. For example, entropy decoding unit 70 may use the updated
probability estimates to decode significant coefficient position
information for subsequently decoded blocks of video data in the
manner described above. It should be noted that, in other examples,
entropy decoding unit 70 may decode the significant coefficient
position information for the block using other techniques.
[0213] Finally, entropy decoding unit 70 may stop decoding the
block (922). For example, entropy decoding unit 70 may proceed to
other coding tasks, e.g., decoding subsequent blocks, as described
above.
[0214] In this manner, the method of FIG. 9 represents an example
of a method of decoding information that identifies a scanning
order associated with a block of video data, including determining
a most probable scanning order for the block, and decoding an
indication of whether the scanning order associated with the block
is the most probable scanning order.
[0215] Therefore, in accordance with the techniques of this
disclosure, an encoded bitstream may comprise scanning order
information for a block of video data, i.e., coefficients
associated with the block. In particular, video encoder 20 may
encode an indication of whether the scanning order associated with
the block is the most probable scanning order. In some examples, in
the event the scanning order associated with the block is not the
most probable scanning order, video encoder 20 may further encode
an indication of the scanning order associated with the block.
Similarly, video decoder 30 may decode the indication of whether
the scanning order associated with the block is the most probable
scanning order. In some examples, in the event the scanning order
associated with the block is not the most probable scanning order,
video decoder 30 may further decode an indication of the scanning
order associated with the block.
[0216] Accordingly, this disclosure also contemplates a
computer-readable medium comprising a data structure stored thereon
that includes an encoded bitstream. The encoded bitstream stored on
the computer-readable medium may comprise video data encoded using
a specific format, and encoded information that identifies a
scanning order associated with a block of video data (i.e.,
scanning order information for the block), represented using one or
more indications. The specific format in which the scanning order
information for the block is encoded within the bitstream depends
on whether the scanning order associated with the block is a most
probable scanning order for the block. More specifically, the
bitstream may include an indication of whether the scanning order
associated with the block is the most probable scanning order. In
some examples, in the event the scanning order does not comprise
the most probable scanning order, the bitstream may further include
an indication of the scanning order associated with the block.
[0217] In one or more examples, the functions described may be
implemented in hardware, software, firmware, or any combination
thereof. If implemented in software, the functions may be stored on
or transmitted over, as one or more instructions or code, a
computer-readable medium and executed by a hardware-based
processing unit. Computer-readable media may include
computer-readable storage media, which corresponds to a tangible
medium such as data storage media, or communication media including
any medium that facilitates transfer of a computer program from one
place to another, e.g., according to a communication protocol. In
this manner, computer-readable media generally may correspond to
(1) tangible computer-readable storage media which is
non-transitory or (2) a communication medium such as a signal or
carrier wave. Data storage media may be any available media that
can be accessed by one or more computers or one or more processors
to retrieve instructions, code and/or data structures for
implementation of the techniques described in this disclosure. A
computer program product may include a computer-readable
medium.
[0218] By way of example, and not limitation, such
computer-readable storage media can comprise RAM, ROM, EEPROM,
CD-ROM or other optical disk storage, magnetic disk storage, or
other magnetic storage devices, flash memory, or any other medium
that can be used to store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Also, any connection is properly termed a
computer-readable medium. For example, if instructions are
transmitted from a website, server, or other remote source using a
coaxial cable, fiber optic cable, twisted pair, digital subscriber
line (DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of medium. It should be
understood, however, that computer-readable storage media and data
storage media do not include connections, carrier waves, signals,
or other transient media, but are instead directed to
non-transient, tangible storage media. Disk and disc, as used
herein, includes compact disc (CD), laser disc, optical disc,
digital versatile disc (DVD), floppy disk and Blu-ray disc, where
disks usually reproduce data magnetically, while discs reproduce
data optically with lasers. Combinations of the above should also
be included within the scope of computer-readable media.
[0219] Instructions may be executed by one or more processors, such
as one or more digital signal processors (DSPs), general purpose
microprocessors, application specific integrated circuits (ASICs),
field programmable logic arrays (FPGAs), or other equivalent
integrated or discrete logic circuitry. Accordingly, the term
"processor," as used herein may refer to any of the foregoing
structure or any other structure suitable for implementation of the
techniques described herein. In addition, in some aspects, the
functionality described herein may be provided within dedicated
hardware and/or software modules configured for encoding and
decoding, or incorporated in a combined codec. Also, the techniques
could be fully implemented in one or more circuits or logic
elements.
[0220] The techniques of this disclosure may be implemented in a
wide variety of devices or apparatuses, including a wireless
handset, an integrated circuit (IC) or a set of ICs (e.g., a chip
set). Various components, modules, or units are described in this
disclosure to emphasize functional aspects of devices configured to
perform the disclosed techniques, but do not necessarily require
realization by different hardware units. Rather, as described
above, various units may be combined in a codec hardware unit or
provided by a collection of interoperative hardware units,
including one or more processors as described above, in conjunction
with suitable software and/or firmware.
[0221] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *