U.S. patent application number 14/533386 was filed with the patent office on 2015-07-09 for modification of picture parameter set (pps) for hevc extensions.
The applicant listed for this patent is ARRIS Enterprises, Inc.. Invention is credited to Limin Wang, Yue Yu.
Application Number | 20150195574 14/533386 |
Document ID | / |
Family ID | 53496202 |
Filed Date | 2015-07-09 |
United States Patent
Application |
20150195574 |
Kind Code |
A1 |
Yu; Yue ; et al. |
July 9, 2015 |
MODIFICATION OF PICTURE PARAMETER SET (PPS) FOR HEVC EXTENSIONS
Abstract
A method, apparatus, article of manufacture, and a memory
structure for signaling extension functions used in decoding a
sequence comprising a plurality of pictures, each picture processed
at least in part according to a picture parameter set is disclosed.
In one embodiment, the method comprises reading a first extension
flag signaling a first extension function in the processing of the
sequence and determining if the first extension flag has a first
value. Further, the method reads a second extension flag signaling
a second extension function in the processing of the sequence and
performs the second extension function according to the read second
extension flag only if the first extension flag has a first
value.
Inventors: |
Yu; Yue; (San Diego, CA)
; Wang; Limin; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ARRIS Enterprises, Inc. |
Suwanee |
GA |
US |
|
|
Family ID: |
53496202 |
Appl. No.: |
14/533386 |
Filed: |
November 5, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61900906 |
Nov 6, 2013 |
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Current U.S.
Class: |
375/240.2 ;
375/240.25 |
Current CPC
Class: |
H04N 19/30 20141101;
H04N 19/70 20141101; H04N 19/46 20141101 |
International
Class: |
H04N 19/625 20060101
H04N019/625; H04N 19/44 20060101 H04N019/44 |
Claims
1. In a processing device for decoding a sequence comprising a
plurality of pictures, each picture processed at least in part
according to a picture parameter set, a method of processing the
sequence, comprising: reading a first extension flag signaling a
first extension function in the processing of the sequence;
determining if the first extension flag has a first value; only if
the first extension flag has a first value: reading a second
extension flag signaling a second extension function in the
processing of the sequence; and performing the second extension
function according to the read second extension flag.
2. The method of claim 1, further comprising: performing the first
extension function according to the read first extension flag after
reading the first extension flag and before reading the second
extension flag; and performing the second extension function
according to the read second extension flag after reading the
second extension flag.
3. The method of claim 2, wherein the second extension function is
functionally related to the first extension function.
4. The method of claim 2, wherein the second extension function is
only implicated in the processing sequence if the first extension
function is implicated in the processing sequence.
5. The method of claim 2, wherein the first extension function
comprises a discrete cosine transforming skip operation.
6. The method of claim 2, wherein: the processed picture comprises
a plurality of transform units; the processing of the sequence
comprises: discrete cosine transforming at least some of the
plurality of transform units of the processed picture; and skipping
discrete cosine transforming of other of the plurality of transform
units at least in part according to a maximum permitted size of the
transform unit; and the first extension function comprises reading
a value indicating the maximum permitted size of the transform unit
for which discrete cosine transforming may be skipped.
7. The method of claim 2, wherein the first function further
comprises a flag read operation signaling the second function.
8. An apparatus for decoding a sequence comprising a plurality of
pictures, each picture processed at least in part according to a
picture parameter set, the apparatus, comprising: a processor; a
memory, communicatively coupled to the processor, the memory
storing a plurality of instructions comprising instructions for:
reading a first extension flag signaling a first extension function
in the processing of the sequence; determining if the first
extension flag has a first value; only if the first extension flag
has a first value: reading a second extension flag signaling a
second extension function in the processing of the sequence; and
performing the second extension function according to the read
second extension flag.
9. The apparatus of claim 8, wherein the instructions further
comprise: performing the first extension function according to the
read first extension flag after reading the first extension flag
and before reading the second extension flag; and performing the
second extension function according to the read second extension
flag after reading the second extension flag.
10. The apparatus of claim 9, wherein the second extension function
is functionally related to the first extension function.
11. The apparatus of claim 9, wherein the second extension function
is only implicated in the processing sequence if the first
extension function is implicated in the processing sequence.
12. The apparatus of claim 9, wherein the first extension function
comprises a discrete cosine transforming skip operation.
13. The apparatus of claim 9, wherein: the processed picture
comprises a plurality of transform units; the instructions for
processing of the sequence comprise: discrete cosine transforming
at least some of the plurality of transform units of the processed
picture; and skipping discrete cosine transforming of other of the
plurality of transform units at least in part according to a
maximum permitted size of the transform unit; and the first
extension function comprises reading a value indicating the maximum
permitted size of the transform unit for which discrete cosine
transforming may be skipped.
14. The apparatus of claim 2, wherein the first function further
comprises a flag read operation signaling the second function.
15. A device for decoding a sequence comprising a plurality of
pictures, each picture processed at least in part according to a
picture parameter set, a method of processing the sequence,
comprising: means for reading a first extension flag signaling a
first extension function in the processing of the sequence; means
for determining if the first extension flag has a first value;
means for reading a second extension flag signaling a second
extension function in the processing of the sequence and performing
the second extension function according to the read second
extension flag only if the first extension flag has a first
value.
16. The device of claim 15, further comprising: means for
performing the first extension function according to the read first
extension flag after reading the first extension flag and before
reading the second extension flag; and means for performing the
second extension function according to the read second extension
flag after reading the second extension flag.
17. The device of claim 15, wherein the second extension function
is functionally related to the first extension function.
18. The device of claim 15, wherein the second extension function
is only implicated in the processing sequence if the first
extension function is implicated in the processing sequence.
19. The device of claim 2, wherein the first extension function
comprises a discrete cosine transforming skip operation.
20. The device of claim 2, wherein: the processed picture comprises
a plurality of transform units; the means for processing of the
sequence comprises: means for discrete cosine transforming at least
some of the plurality of transform units of the processed picture;
and means for skipping discrete cosine transforming of other of the
plurality of transform units at least in part according to a
maximum permitted size of the transform unit; and the first
extension function comprises reading a value indicating the maximum
permitted size of the transform unit for which discrete cosine
transforming may be skipped.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of the following U.S.
Provisional Patent application, which is hereby incorporated by
reference: Application Ser. No. 61/900,906, entitled "THE
MODIFICATION OF PICTURE PARAMETER SET (PPS) FOR HEVC RANGE
EXTENSION," by Yue Yu and Limin Wang, filed Nov. 6, 2013.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to systems and methods for
encoding data, and in particular to a system and method for
generating and processing slice headers with high efficiency video
coded data.
[0004] 2. Description of the Related Art
[0005] There is rapid growth in the technologies associated with
the generation, transmission, and reproduction of media programs.
These technologies include coding schemes that permit digital
versions of the media programs to be encoded to compress them to
much smaller size and facilitate their transmission, storage,
reception and playback. These technologies have application in
personal video recorders (PVRs), video on demand (VOD), multiple
channel media program offerings, interactivity, mobile telephony,
and media program transmission.
[0006] Without compression, digital media programs are typically
too large to transmit and/or store for a commercially acceptable
cost. However, compression of such programs has made the
transmission and storage of such digital media programs not only
commercially feasible, but commonplace.
[0007] Initially, the transmission of media programs involved low
to medium resolution images transmitted over high bandwidth
transmission media such as cable television and satellite. However,
such transmission has evolved to include lower bandwidth
transmission media such as Internet transmission to fixed and
mobile devices via computer networks, WiFi, Mobile TV and third and
fourth generation (3G and 4G) networks. Further, such transmissions
have also evolved to include high definition media programs such as
high definition television (HDTV), which have significant
transmission bandwidth and storage requirements.
[0008] The High Efficiency Video Coding (HEVC) coding standard (or
H.265) is the most recent coding standard promulgated by the
ISO/IEC MPEG standardization organizations. The coding standard
preceding HEVC included the H.262/MPEG-2 and the subsequent
H.264/MPEG-4 Advanced Video Coding (AVC) standard. H.264/MPEG-4 has
substantially replaced H.262/MPEG-2 in many application including
high definition (HD) television. HEVC supports resolutions higher
than HD, even in stereo or multi-view embodiments, and is more
suitable for mobile devices such as tablet personal computers.
Further information regarding HEVC can be found in the publication
"Overview of the High Efficiency Video Coding (HEVC) Standard, by
Gary J. Sullivan, Jens-Rainer Ohm, Woo Jin Han and Thomas Wiegand,
IEEE Transactions on Circuits and Systems for Video Technology,
December 2012, which is hereby incorporated by reference
herein.
[0009] As in other coding standards, the bitstream structure and
syntax of HEVC compliant data are standardized, such that every
decoder conforming to the standard will produce the same output
when provided with the same input. Some of the features
incorporated into the HEVC standard include the definition and
processing of a slice, one or more of which may together comprise
one of the pictures in a video sequence. A video sequence comprises
a plurality of pictures, and each picture may comprise one or more
slices. Slices include non-dependent slices and dependent slices. A
non-dependent slice (hereinafter simply referred to as a slice) is
a data structure that can be decoded independently from other
slices of the same picture in terms of entropy encoding, signal
prediction, and residual signal construction. This data structure
permits resynchronization of events in case of data losses. A
"dependent slice" is a structure that permits information about the
slice (such as those related with tiles within the slice or
wavefront entries) to be carried to the network layer, thus making
that data available to a system to more quickly process fragmented
slices. Dependent slices are mostly useful for low-delay
encoding.
[0010] HEVC and legacy coding standards define a parameter set
structure that offers improved flexibility for operation over a
wide variety of applications and network environments, and improved
robustness to data losses. Parameter sets contain information that
can be shared for decoding of different portions of the encoded
video. The parameter set structure provides a secure mechanism for
conveying data that is essential to the decoding process. H.264
defined both sequence parameter sets (SPS) that describe parameters
for decoding a sequence of pictures and a picture parameter set
(PPS) that describes parameters for decoding a picture of the
sequence of pictures. HEVC introduces a new parameter set, the
video parameter set (VPS).
[0011] The encoding and decoding of slices is performed according
to information included in a slice header. The slice header
includes syntax and logic for reading flags and data that are used
in decoding the slice.
[0012] Like its predecessors, HEVC supports both temporal and
spatial encoding of picture slices. HEVC defines slices to include
I-slices, which are spatially, but not temporally encoded with
reference to another slice. I-slices are alternatively described as
"intra" slice encoded. HEVC also defines slices to include P
(predictive) slices, which are spatially encoded and temporally
encoded with reference to another slice. P-slices are alternatively
described as "inter" slice encoded. HEVC also describes slices to
include bi-predictive (B)-slices. B-slices are spatially encoded
and temporally encoded with reference to two or more other slices.
Further, HEVC consolidates the notion of P and B slices into
general B slices that can be used as reference slice.
[0013] Currently, the HEVC syntax includes provision for extensions
to expand the capabilities or capacities of HEVC beyond the
baseline. Such extensions include range extensions (RExt,
scalability extensions (SHVC), and multi-view extensions (MV-HEVC).
Extensions may be signaled in the VPS, SPS, PPS, or combination
thereof.
[0014] Currently, the PPS syntax, defines both range and multilayer
extensions, as described in paragraphs 7.3.2.2.2 and 7.3.2.2.3 of
"Draft high efficiency video coding (HEVC) version 2, combined
format range extensions (RExt), scalability (SHVC), and multi-view
(MV-HEVC) extensions," Draft ISO/IEC 23008-2:201x(E)
JCTVC-R1013_v6, published by the Joint Collaborative Team on Video
Coding OCT-VC), on Jun. 30, 2014 by Jill Boyce et al., which is
hereby incorporated by reference herein. However, this standard
provides for the handling of extension flags and extensions that
are functionally independent from one another (e.g. the presence of
a particular extension does not make the presence of another
particular extension more probable, and hence, are evaluated in
order, one at a time, without regard to the notion that the absence
of one extension necessarily implicates that another extension is
not present or implicated. While this standard is adequate for
cases where the extensions are truly independent, it can result in
wasted operations and instructions when the extensions are not.
Accordingly, there is a need for a PPS syntax that efficiently
provides for extensions that are not independent. This disclosure
presents a description of a PPS syntax that satisfies this
need.
SUMMARY
[0015] To address the requirements described above, this document
discloses a memory structure for signaling extension functions used
in decoding a sequence comprising a plurality of pictures, each
picture processed at least in part according to a picture parameter
set is disclosed. In one embodiment, the method comprises reading a
first extension flag signaling a first extension function in the
processing of the sequence and determining if the first extension
flag has a first value. Further, the method reads a second
extension flag signaling a second extension function in the
processing of the sequence and performs the second extension
function according to the read second extension flag only if the
first extension flag has a first value. Another embodiment is
disclosed in which an apparatus is evidenced by a processor having
a communicatively coupled memory storing instructions for
performing the foregoing operations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Referring now to the drawings in which like reference
numbers represent corresponding parts throughout:
[0017] FIG. 1 is a diagram depicting an exemplary embodiment of a
video coding-decoding system that can be used for transmission
and/or storage and retrieval of audio and/or video information;
[0018] FIG. 2A is a diagram of one embodiment of a codec system in
which the encoded AV information is transmitted to and received at
another location;
[0019] FIGS. 2B-2C provide diagrams depicting embodiments of codec
systems;
[0020] FIG. 3 is a block diagram illustrating one embodiment of the
source encoder;
[0021] FIG. 4 is a diagram depicting a picture of AV information,
such as one of the pictures in the picture sequence;
[0022] FIG. 5 is a diagram showing an exemplary partition of a
coding tree block into coding units;
[0023] FIG. 6 is a diagram illustrating a representation of a
representative quadtree and data parameters for the code tree block
partitioning shown in FIG. 5;
[0024] FIG. 7 is a diagram illustrating the partition of a coding
unit into one or more prediction units;
[0025] FIG. 8 is a diagram showing a coding unit partitioned into
four prediction units and an associated set of transform units;
[0026] FIG. 9 is a diagram showing RQT codetree for the transform
units associated with the coding unit in the example of FIG. 8;
[0027] FIG. 10 is a diagram illustrating spatial prediction of
prediction units;
[0028] FIG. 11 is a diagram illustrating temporal prediction;
[0029] FIG. 12 is a diagram illustrating the use of motion vector
predictors (MVPs);
[0030] FIG. 13 illustrates an example of the use of the reference
picture lists;
[0031] FIG. 14 is a diagram illustrating processes performed by the
encoder according to the aforementioned standard;
[0032] FIG. 15 depicts the use of a the
collocated_from.sub.--10_flag by the decoder in decoding a
according to the emerging HEVC standard;
[0033] FIGS. 16A and 16B are diagrams presenting a baseline PPS
syntax;
[0034] FIGS. 16C and 16D are diagrams presenting an improved PPS
syntax;
[0035] FIG. 17 illustrates an exemplary processing system that
could be used to implement the embodiments of the invention.
DETAILED DESCRIPTION
[0036] In the following description, reference is made to the
accompanying drawings which form a part hereof, and which is shown,
by way of illustration, several embodiments of the present
invention. It is understood that other embodiments may be utilized
and structural changes may be made without departing from the scope
of the present invention.
Audio-Visual Information Transception and Storage
[0037] FIG. 1 is a diagram depicting an exemplary embodiment of a
video coding-decoding (codec) system 100 that can be used for
transmission and/or storage and retrieval of audio and/or video
information. The codec system 100 comprises an encoding system 104,
which accepts audio-visual (AV) information 102 and processes the
AV information 102 to generate encoded (compressed) AV information
106, and a decoding system 112, which processes the encoded AV
information 106 to produce recovered AV information 114. Since the
encoding and decoding processes are not lossless, the recovered AV
information 114 is not identical to the initial AV information 102,
but with judicious selection of the encoding processes and
parameters, the differences between the recovered AV information
114 and the unprocessed AV information 102 are acceptable to human
perception.
[0038] The encoded AV information 106 is typically transmitted or
stored and retrieved before decoding and presentation, as performed
by transception (transmission and reception) or storage/retrieval
system 108. Transception losses may be significant, but
storage/retrieval losses are typically minimal or non-existent,
hence, the transcepted AV information 110 provided to the decoding
system 112 is typically the same as or substantially the same as
the encoded AV information 106.
[0039] FIG. 2A is a diagram of one embodiment of a codec system
200A in which the encoded AV information 106 is transmitted to and
received at another location. A transmission segment 230 converts
an input AV information 102 into a signal appropriate for
transmission and transmits the converted signal over the
transmission channel 212 to the reception segment 232. The
reception segment 232 receives the transmitted signal, and converts
the received signal into the recovered AV information 114 for
presentation. As described above, due to coding and transmission
losses and errors, the recovered AV information 114 may be of lower
quality than the AV information 102 that was provided to the
transmission segment 230. However, error-correcting systems may be
included to reduce or eliminate such errors. For example, the
encoded AV information 106 may be forward error correction (FEC)
encoded by adding redundant information, and such redundant
information can be used to identify and eliminate errors in the
reception segment 230.
[0040] The transmission segment 102 comprises one or more source
encoders 202 to encode multiple sources of AV information 102. The
source encoder 202 encodes the AV information 102 primarily for
purposes of compression to produce the encoded AV information 106,
and may include, for example a processor and related memory storing
instructions implementing a codec such as MPEG-1, MPEG-2, MPEG-4
AVC/H.264, HEVC or similar codec, as described further below.
[0041] The codec system 200A may also include optional elements
indicated by the dashed lines in FIG. 2A. These optional elements
include a video multiplex encoder 204, an encoding controller 208,
and a video demultiplexing decoder 218. The optional video
multiplex encoder 204 multiplexes encoded AV information 106 from
an associated plurality of source encoder(s) 202 according to one
or more parameters supplied by the optional encoding controller
208. Such multiplexing is typically accomplished in the time domain
and is data packet based.
[0042] In one embodiment, the video multiplex encoder 204 comprises
a statistical multiplexer, which combines the encoded AV
information 106 from a plurality of source encoders 202 so as to
minimize the bandwidth required for transmission. This is possible,
since the instantaneous bit rate of the coded AV information 106
from each source encoder 202 can vary greatly with time according
to the content of the AV information 102. For example, scenes
having a great deal of detail and motion (e.g. sporting events) are
typically encoded at higher bitrates than scenes with little motion
or detail (e.g. portrait dialog). Since each source encoder 202 may
produce information with a high instantaneous bitrate while another
source encoder 202 produces information with a low instantaneous
bit rate, and since the encoding controller 208 can command the
source encoders 202 to encode the AV information 106 according to
certain performance parameters that affect the instantaneous bit
rate, the signals from each of the source encoders 106 (each having
a temporally varying instantaneous bit rate) can be combined
together in an optimal way to minimize the instantaneous bit rate
of the multiplexed stream 205.
[0043] As described above, the source encoder 202 and the video
multiplex coder 204 may optionally be controlled by a coding
controller 208 to minimize the instantaneous bit rate of the
combined video signal. In one embodiment, this is accomplished
using information from a transmission buffer 206 which temporarily
stores the coded video signal and can indicate the fullness of the
buffer 206. This allows the coding performed at the source encoder
202 or video multiplex coder 204 to be a function of the storage
remaining in the transmission buffer 206.
[0044] The transmission segment 230 also may comprise a
transmission encoder 210, which further encodes the video signal
for transmission to the reception segment 232. Transmission
encoding may include for example, the aforementioned FEC coding
and/or coding into a multiplexing scheme for the transmission
medium of choice. For example, if the transmission is by satellite
or terrestrial transmitters, the transmission encoder 114 may
encode the signal into a signal constellation before transmission
via quadrature amplitude modulation (QAM) or similar modulation
technique. Also, if the encoded video signal is to be streamed via
an Internet protocol device and the Internet, the transmission
encodes the signal according to the appropriate protocol. Further,
if the encoded signal is to be transmitted via mobile telephony,
the appropriate coding protocol is used, as further described
below.
[0045] The reception segment 232 comprises a transmission decoder
214 to receive the signal that was coded by the transmission coder
210 using a decoding scheme complementary to the coding scheme used
in the transmission encoder 214. The decoded received signal may be
temporarily stored by optional reception buffer 216, and if the
received signal comprises multiple video signals, the received
signal is multiplex decoded by video multiplex decoder 218 to
extract the video signal of interest from the video signals
multiplexed by the video multiplex coder 204. Finally, the video
signal of interest is decoded by source decoder 220 using a
decoding scheme or codec complementary to the codec used by the
source encoder 202 to encode the AV information 102.
[0046] In one embodiment, the transmitted data comprises a
packetized video stream transmitted from a server (representing the
transmitting segment 230) to a client (representing the receiving
segment 232). In this case, the transmission encoder 210 may
packetize the data and embed network abstract layer (NAL) units in
network packets. NAL units define a data container that has header
and coded elements, and may correspond to a video frame or other
slice of video data.
[0047] The compressed data to be transmitted may packetized and
transmitted via transmission channel 212, which may include a Wide
Area Network (WAN) or a Local Area Network (LAN). Such a network
may comprise, for example, a wireless network such as WiFi, an
Ethernet network, an Internet network or a mixed network composed
of several different networks. Such communication may be affected
via a communication protocol, for example Real-time Transport
Protocol (RTP), User Datagram Protocol (UDP) or any other type of
communication protocol. Different packetization methods may be used
for each network abstract layer (NAL) unit of the bitstream. In one
case, one NAL unit size is smaller than the maximum transport unit
(MTU) size corresponding to the largest packet size that can be
transmitted over the network without being fragmented. In this
case, the NAL unit is embedded into a single network packet. In
another case, multiple entire NAL units are included in a single
network packet. In a third case, one NAL unit may be too large to
be transmitted in a single network packet and is thus split into
several fragmented NAL units with each fragmented NAL unit being
transmitted in an individual network packet. Fragmented NAL unit
are typically sent consecutively for decoding purposes.
[0048] The reception segment 232 receives the packetized data and
reconstitutes the NAL units from the network packet. For fragmented
NAL units, the client concatenates the data from the fragmented NAL
units in order to reconstruct the original NAL unit. The client 232
decodes the received and reconstructed data stream and reproduces
the video images on a display device and the audio data by a loud
speaker.
[0049] FIG. 2B is a diagram depicting an exemplary embodiment of
codec system in which the encoded information is stored and later
retrieved for presentation, hereinafter referred to as codec
storage system 200B. This embodiment may be used, for example, to
locally store information in a digital video recorder (DVR), a
flash drive, hard drive, or similar device. In this embodiment, the
AV information 102 is source encoded by source encoder 202,
optionally buffered by storage buffer 234 before storage in a
storage device 236. The storage device 236 may store the video
signal temporarily or for an extended period of time, and may
comprise a hard drive, flash drive, RAM or ROM. The stored AV
information is then retrieved, optionally buffered by retrieve
buffer 238 and decoded by the source decoder 220.
[0050] FIG. 2C is another diagram depicting an exemplary content
distribution system 200C comprising a coding system or encoder 202
and a decoding system or decoder 220 that can be used to transmit
and receive HEVC data. In some embodiments, the coding system 202
can comprise an input interface 256, a controller 241 a counter 242
a frame memory 243, an encoding unit 244, a transmitter buffer 267
and an output interface 257. The decoding system 220 can comprise a
receiver buffer 259, a decoding unit 260, a frame memory 261 and a
controller 267. The coding system 202 and the decoding system 220
can be coupled with each other via a transmission path which can
carry a compressed bit stream. The controller 241 of the coding
system 202 can control the amount of data to be transmitted on the
basis of the capacity of the transmitter buffer 267 or receiver
buffer 259 and can include other parameters such as the amount of
data per a unit of time. The controller 241 can control the
encoding unit 244 to prevent the occurrence of a failure of a
received signal decoding operation of the decoding system 220. The
controller 241 can be a processor or include, by way of a
non-limiting example, a microcomputer having a processor, a random
access memory and a read only memory.
[0051] Source pictures 246 supplied from, by way of a non-limiting
example, a content provider can include a video sequence of frames
including source pictures in a video sequence. The source pictures
246 can be uncompressed or compressed. If the source pictures 246
are uncompressed, the coding system 202 can have an encoding
function. If the source pictures 246 are compressed, the coding
system 202 can have a transcoding function. Coding units can be
derived from the source pictures utilizing the controller 241. The
frame memory 243 can have a first area that can be used for storing
the incoming frames from the source pictures 246 and a second area
that can be used for reading out the frames and outputting them to
the encoding unit 244. The controller 241 can output an area
switching control signal 249 to the frame memory 243. The area
switching control signal 249 can indicate whether the first area or
the second area is to be utilized.
[0052] The controller 241 can output an encoding control signal 250
to the encoding unit 244. The encoding control signal 250 can cause
the encoding unit 202 to start an encoding operation, such as
preparing the Coding Units based on a source picture. In response
to the encoding control signal 250 from the controller 241, the
encoding unit 244 can begin to read out the prepared Coding Units
to a high-efficiency encoding process, such as a prediction coding
process or a transform coding process which process the prepared
Coding Units generating video compression data based on the source
pictures associated with the Coding Units.
[0053] The encoding unit 244 can package the generated video
compression data in a packetized elementary stream (PES) including
video packets. The encoding unit 244 can map the video packets into
an encoded video signal 248 using control information and a program
time stamp (PTS) and the encoded video signal 248 can be
transmitted to the transmitter buffer 267.
[0054] The encoded video signal 248, including the generated video
compression data, can be stored in the transmitter buffer 267. The
information amount counter 242 can be incremented to indicate the
total amount of data in the transmitter buffer 267. As data is
retrieved and removed from the buffer, the counter 242 can be
decremented to reflect the amount of data in the transmitter buffer
267. The occupied area information signal 253 can be transmitted to
the counter 242 to indicate whether data from the encoding unit 244
has been added or removed from the transmitter buffer 267 so the
counter 242 can be incremented or decremented. The controller 241
can control the production of video packets produced by the
encoding unit 244 on the basis of the occupied area information 253
which can be communicated in order to anticipate, avoid, prevent,
and/or detect an overflow or underflow from taking place in the
transmitter buffer 267.
[0055] The information amount counter 242 can be reset in response
to a preset signal 254 generated and output by the controller 241.
After the information amount counter 242 is reset, it can count
data output by the encoding unit 244 and obtain the amount of video
compression data and/or video packets, which have been generated.
The information amount counter 242 can supply the controller 241
with an information amount signal 255 representative of the
obtained amount of information. The controller 241 can control the
encoding unit 244 so that there is no overflow at the transmitter
buffer 267.
[0056] In some embodiments, the decoding system 220 can comprise an
input interface 266, a receiver buffer 259, a controller 267, a
frame memory 261, a decoding unit 260 and an output interface 267.
The receiver buffer 259 of the decoding system 220 can temporarily
store the compressed bit stream, including the received video
compression data and video packets based on the source pictures
from the source pictures 246. The decoding system 220 can read the
control information and presentation time stamp information
associated with video packets in the received data and output a
frame number signal 263 which can be applied to the controller 220.
The controller 267 can supervise the counted number of frames at a
predetermined interval. By way of a non-limiting example, the
controller 267 can supervise the counted number of frames each time
the decoding unit 260 completes a decoding operation.
[0057] In some embodiments, when the frame number signal 263
indicates the receiver buffer 259 is at a predetermined capacity,
the controller 267 can output a decoding start signal 264 to the
decoding unit 260. When the frame number signal 263 indicates the
receiver buffer 259 is at less than a predetermined capacity, the
controller 267 can wait for the occurrence of a situation in which
the counted number of frames becomes equal to the predetermined
amount. The controller 267 can output the decoding start signal 263
when the situation occurs. By way of a non-limiting example, the
controller 267 can output the decoding start signal 264 when the
frame number signal 263 indicates the receiver buffer 259 is at the
predetermined capacity. The encoded video packets and video
compression data can be decoded in a monotonic order (i.e.,
increasing or decreasing) based on presentation time stamps
associated with the encoded video packets.
[0058] In response to the decoding start signal 264, the decoding
unit 260 can decode data amounting to one picture associated with a
frame and compressed video data associated with the picture
associated with video packets from the receiver buffer 259. The
decoding unit 260 can write a decoded video signal 269 into the
frame memory 261. The frame memory 261 can have a first area into
which the decoded video signal is written, and a second area used
for reading out decoded pictures 262 to the output interface
267.
[0059] In various embodiments, the coding system 202 can be
incorporated or otherwise associated with a transcoder or an
encoding apparatus at a headend and the decoding system 220 can be
incorporated or otherwise associated with a downstream device, such
as a mobile device, a set top box or a transcoder.
Source Encoding/Decoding
[0060] As described above, the encoders 202 employ compression
algorithms to generate bit streams and/or files of smaller size
than the original video sequences in the AV information 102. Such
compression is made possible by reducing spatial and temporal
redundancies in the original sequences.
[0061] Prior art encoders 202 include those compliant with the
video compression standard H.264/MPEG-4 AVC ("Advanced Video
Coding") developed by between the "Video Coding Expert Group"
(VCEG) of the ITU and the "Moving Picture Experts Group" (MPEG) of
the ISO, in particular in the form of the publication "Advanced
Video Coding for Generic Audiovisual Services" (March 2005), which
is hereby incorporated by reference herein.
[0062] HEVC "High Efficiency Video Coding" (sometimes known as
H.265) is expected to replace the H.264/MPEG-4 AVC. HEVC introduces
new coding tools and entities that are generalizations of the
coding entities defined in H.264/AVC, as further described
below.
[0063] FIG. 3 is a block diagram illustrating one embodiment of the
source encoder 202. The source encoder 202 accepts AV information
102 and uses sampler 302 sample the AV information 102 to produce a
sequence 303 of successive of digital images or pictures, each
having a plurality of pixels. A picture can comprise a frame or a
field, wherein a frame is a complete image captured during a known
time interval, and a field is the set of odd-numbered or
even-numbered scanning lines composing a partial image.
[0064] The sampler 302 produces an uncompressed picture sequence
303. Each digital picture can be represented by one or more
matrices having a plurality of coefficients that represent
information about the pixels that together comprise the picture.
The value of a pixel can correspond to luminance or other
information. In the case where several components are associated
with each pixel (for example red-green-blue components or
luminance-chrominance components), each of these components may be
separately processed.
[0065] Images can be segmented into "slices," which may comprise a
portion of the picture or may comprise the entire picture. In the
H.264 standard, these slices are divided into coding entities
called macroblocks (generally blocks of size 16 pixels.times.16
pixels) and each macroblock may in turn be divided into different
sizes of data blocks 102, for example 4.times.4, 4.times.8,
8.times.4, 8.times.8, 8.times.16, 16.times.8. HEVC expands and
generalizes the notion of the coding entity beyond that of the
macroblock.
HEVC Coding Entities: CTU, CU, PU and TU
[0066] Like other video coding standards, HEVC is a block-based
hybrid spatial and temporal predictive coding scheme. However, HEVC
introduces new coding entities that are not included with H.264/AVC
standard. These coding entities include (1) Coding tree block
(CTUs), coding units (CUs), the predictive units (PUs) and
transform units (TUs) and are further described below.
[0067] FIG. 4 is a diagram depicting a picture 400 of AV
information 102, such as one of the pictures in the picture
sequence 303. The picture 400 is spatially divided into
non-overlapping square blocks known as coding tree units(s), or
CTUs 402. Unlike H.264 and previous video coding standards where
the basic coding unit is macroblock of 16.times.16 pixels, the CTU
402 is the basic coding unit of HEVC, and can be as large as
128.times.128 pixels. As shown in FIG. 4, the CTUs 402 are
typically referenced within the picture 400 in an order analogous
to a progressive scan.
[0068] Each CTU 402 may in turn be iteratively divided into smaller
variable size coding units described by a "quadtree" decomposition
further described below. Coding units are regions formed in the
image to which similar encoding parameters are applied and
transmitted in the bitstream 314.
[0069] FIG. 5 is a diagram showing an exemplary partition of an CTU
402 into coding units (CUs) such as coding unit 502A and 502B
(hereinafter alternatively referred to as coding unit(s) 502). A
single CTU 402 can be divided into four CUs 502 such as CU 502A,
each a quarter of the size of CTU 402. Each such divided CU 502A
can be further divided into four smaller CUs 502B of quarter size
of initial CU 502A.
[0070] The division of CTUs 402 into CUs 502A and into smaller CUs
502B is described by "quadtree" data parameters (e.g. flags or
bits) that are encoded into the output bitstream 314 along with the
encoded data as overhead known as syntax.
[0071] FIG. 6 is a diagram illustrating a representation of a
representative quadtree 600 and data parameters for the CTU 402
partitioning shown in FIG. 5. The quadtree 600 comprises a
plurality of nodes including first node 602A at one hierarchical
level and second node 602B at a lower hierarchical level
(hereinafter, quadtree nodes may be alternatively referred to as
"nodes" 602). At each node 602 of a quadtree, a "split flag" or bit
"1" is assigned if the node 602 is further split into sub-nodes,
otherwise a bit "0" is assigned.
[0072] For example, the CTU 402 partition illustrated in FIG. 5 can
be represented by the quadtree 600 presented in FIG. 6, which
includes a split flag of "1" associated with node 602A at the top
CU 502 level (indicating there are 4 additional nodes at a lower
hierarchical level). The illustrated quadtree 600 also includes a
split flag of "1" associated with node 602B at the mid CU 502 level
to indicate that this CU is also partitioned into four further CUs
502 at the next (bottom) CU level. The source encoder 202 may
restrict the minimum and maximum CU 502 sizes, thus changing the
maximum possible depth of the CU 502 splitting.
[0073] The encoder 202 generates encoded AV information 106 in the
form of a bitstream 314 that includes a first portion having
encoded data for the CUs 502 and a second portion that includes
overhead known as syntax elements. The encoded data includes data
corresponding to the encoded CUs 502 (i.e. the encoded residuals
together with their associated motion vectors, predictors, or
related residuals as described further below). The second portion
includes syntax elements that may represent encoding parameters
which do not directly correspond to the encoded data of the blocks.
For example, the syntax elements may comprise an address and
identification of the CU 502 in the image, a quantization
parameter, an indication of the elected Inter/Intra coding mode,
the quadtree 600 or other information.
[0074] CUs 502 correspond to elementary coding elements and include
two related sub-units: prediction units (PUs) and a transform units
(TUs), both of which have a maximum size equal to the size of the
corresponding CU 502.
[0075] FIG. 7 is a diagram illustrating the partition of a CU 502
into one or more PUs 702. A PU 702 corresponds to a partitioned CU
502 and is used to predict pixels values for intra-picture or
inter-picture types. PUs 702 are an extension of the partitioning
of H.264/AVC for motion estimation, and are defined for each CU 502
that is not further subdivided into other CUs ("split flag"=0). At
each leaf 604 of the quadtree 600, a final (bottom level) CU 502 of
2N.times.2N can possess one of four possible patterns of PUs:
2N.times.2N (702A), 2N.times.N (702B), N.times.2N (702C) and
N.times.N (702D)), as shown in FIG. 7.
[0076] A CU 502 can be either spatially or temporally predictive
coded. If a CU 502 is coded in "intra" mode, each PU 702 of the CU
502 can have its own spatial prediction direction and image
information as further described below. Also, in the "intra" mode,
the PU 702 of the CU 502 may depend on another CU 502 because it
may use a spatial neighbor, which is in another CU. If a CU 502 is
coded in "inter" mode, each PU 702 of the CU 502 can have its own
motion vector(s) and associated reference picture(s) as further
described below.
[0077] FIG. 8 is a diagram showing a CU 502 partitioned into four
PUs 702 and an associated set of transform units (TUs) 802. TUs 802
are used to represent the elementary units that are spatially
transformed by a DCT (Discrete Cosine Transform). The size and
location of each block transform TU 802 within a CU 502 is
described by a "residual" quadtree (RQT) further illustrated
below.
[0078] FIG. 9 is a diagram showing RQT 900 for TUs 802 for the CU
502 in the example of FIG. 8. Note that the "1" at the first node
902A of the RQT 900 indicates that there are four branches and that
the "1" at the second node 902B at the adjacent lower hierarchical
level indicates that the indicated node further has four branches.
The data describing the RQT 900 is also coded and transmitted as an
overhead in the bitstream 314.
[0079] The coding parameters of a video sequence may be stored in
dedicated NAL units called parameter sets. Two types of parameter
sets NAL units may be employed. The first parameter set type is
known as a Sequence Parameter Set (SPS), and comprises a NAL unit
that includes parameters that are unchanged during the entire video
sequence. Typically, an SPS handles the coding profile, the size of
the video frames and other parameters. The second type of parameter
set is known as a Picture Parameter Set (PPS), and codes different
values that may change from one image to another.
Spatial and Temporal Prediction
[0080] One of the techniques used to compress a bitstream 314 is to
forego the storage of pixel values themselves and instead, predict
the pixel values using a process that can be repeated at the
decoder 220 and store or transmit the difference between the
predicted pixel values and the actual pixel values (known as the
residual). So long as the decoder 220 can compute the same
predicted pixel values from the information provided, the actual
picture values can be recovered by adding the residuals to the
predicted values. The same technique can be used to compress other
data as well.
[0081] Referring back to FIG. 3, each PU 702 of the CU 502 being
processed is provided to a predictor module 307. The predictor
module 307 predicts the values of the PUs 702 based on information
in nearby PUs 702 in the same frame (intra-frame prediction, which
is performed by the spatial predictor 324) and information of PUs
702 in temporally proximate frames (inter-frame prediction, which
is performed by the temporal predictor 330). Temporal prediction,
however, may not always be based on a collocated PU, since
collocated PUs are defined to be located at a
reference/non-reference frame having the same x and y coordinates
as the current PU 702. These techniques take advantage of spatial
and temporal dependencies between PUs 702.
[0082] Encoded units can therefore be categorized to include two
types: (1) non-temporally predicted units and (2) temporally
predicted units. Non-temporally predicted units are predicted using
the current frame, including adjacent or nearby PUs 702 within the
frame (e.g. intra-frame prediction), and are generated by the
spatial predictor 324. Temporally predicted units are predicted
from one temporal picture (e.g. P-frames) or predicted from at
least two reference pictures temporally ahead and/or behind (i.e.
B-frames).
Spatial Prediction
[0083] FIG. 10 is a diagram illustrating spatial prediction of PUs
702. A picture may comprise a PU 702 and spatially proximate other
PUs 1-4, including nearby PU 702N. The spatial predictor 324
predicts the current block (e.g. block C of FIG. 10) by means of an
"intra-frame" prediction which uses PUs 702 of already-encoded
other blocks of pixels of the current image.
[0084] The spatial predictor 324 locates a nearby PU (e.g. PU 1, 2,
3 or 4 of FIG. 10) that is appropriate for spatial coding and
determines an angular prediction direction to that nearby PU. In
HEVC, 35 directions can be considered, so each PU may have one of
35 directions associated with it, including horizontal, vertical,
45 degree diagonal, 135 degree diagonal, DC etc. The spatial
prediction direction of the PU is indicated in the syntax.
[0085] Referring back to the spatial predictor 324 of FIG. 3, this
located nearby PU is used to compute a residual PU 704 (e) as the
difference between the pixels of the nearby PU 702N and the current
PU 702, using element 305. The result is an intra-predicted PU
element 1006 that comprises a prediction direction 1002 and the
intra-predicted residual PU 1004. The prediction direction 1002 may
be coded by inferring the direction from spatially proximate PUs,
and the spatial dependencies of the picture, enabling the coding
rate of the intra prediction direction mode to be reduced.
Temporal Prediction
[0086] FIG. 11 is a diagram illustrating temporal prediction.
Temporal prediction considers information from temporally
neighboring pictures or frames, such as the previous picture,
picture i-1.
[0087] Generally, temporal prediction includes single-prediction
(P-type), which predicts the PU 702 by referring to one reference
area from only one reference picture, and multiple prediction
(B-type), which predicts the PU by referring to two reference areas
from one or two reference pictures. Reference images are images in
the video sequence that have already been coded and then
reconstructed (by decoding).
[0088] The temporal predictor 330 identifies, in one or several of
these reference areas (one for P-type or several for B-type), areas
of pixels in a temporally nearby frame so that they can be used as
predictors of this current PU 702. In the case where several areas
predictors are used (B-type), they may be merged to generate one
single prediction. The reference area 1102 is identified in the
reference frame by a motion vector (MV) 1104 that is defines the
displacement between the current PU 702 in current frame (picture
i) and the reference area 1102 (refIdx) in the reference frame
(picture i-1). A PU in a B-picture may have up to two MVs. Both MV
and refIdx information are included in the syntax of the HEVC
bitstream.
[0089] Referring again to FIG. 3, a difference between the pixel
values between of the reference area 1102 and the current PU 702
may be computed by element 305 as selected by switch 306. This
difference is referred to as the residual of the inter-predicted PU
1106. At the end of the temporal or inter-frame prediction process,
the current PU 1006 is composed of one motion vector MV 1104 and a
residual 1106.
[0090] However, as described above, one technique for compressing
data is to generate predicted values for the data using means
repeatable by the decoder 220, computing the difference between the
predicted and actual values of the data (the residual) and
transmitting the residual for decoding. So long as the decoder 220
can reproduce the predicted values, the residual values can be used
to determine the actual values.
[0091] This technique can be applied to the MVs 1104 used in
temporal prediction by generating a prediction of the MV 1104,
computing a difference between the actual MV 1104 and the predicted
MV 1104 (a residual) and transmitting the MV residual in the
bitstream 314. So long as the decoder 220 can reproduce the
predicted MV 1104, the actual MV 1104 can be computed from the
residual. HEVC computes a predicted MV for each PU 702 using the
spatial correlation of movement between nearby PUs 702.
[0092] FIG. 12 is a diagram illustrating the use of motion vector
predictors (MVPs) in HEVC. Motion vector predictors V.sub.1,
V.sub.2 and V.sub.3 are taken from the MVs 1104 of a plurality of
blocks 1, 2, and 3 situated nearby or adjacent the block to encode
(C). As these vectors refer to motion vectors of spatially
neighboring blocks within the same temporal frame and can be used
to predict the motion vector of the block to encode, these vectors
are known as spatial motion predictors.
[0093] FIG. 12 also illustrates temporal motion vector predictor
V.sub.T which is the motion vector of the co-located block C' in a
previously decoded picture (in decoding order) of the sequence (e.
g. block of picture i-1 located at the same spatial position as the
block being coded (block C of image i).
[0094] The components of the spatial motion vector predictors
V.sub.1, V.sub.2 and V.sub.3 and the temporal motion vector
predictor V.sub.T can be used to generate a median motion vector
predictor V.sub.M. In HEVC, the three spatial motion vector
predictors may be taken as shown in FIG. 12, that is, from the
block situated to the left of the block to encode (V.sub.1), the
block situated above (V.sub.3) and from one of the blocks situated
at the respective corners of the block to encode (V.sub.2),
according to a predetermined rule of availability. This MV
predictor selection technique is known as Advanced Motion Vector
Prediction (AMVP).
[0095] A plurality of (typically five) MV predictor (MVP)
candidates having spatial predictors (e.g. V.sub.1, V.sub.2 and
V.sub.3) and temporal predictor(s) V.sub.T is therefore obtained.
In order to reduce the overhead of signaling the motion vector
predictor in the bitstream, the set of motion vector predictors may
reduced by eliminating data for duplicated motion vectors (for
example, MVs which have the same value as other MVs may be
eliminated from the candidates).
[0096] The encoder 202 may select a "best" motion vector predictor
from among the candidates, and compute a motion vector predictor
residual as a difference between the selected motion vector
predictor and the actual motion vector, and transmit the motion
vector predictor residual in the bitstream 314. To perform this
operation, the actual motion vector must be stored for later use by
the decoder 220 (although it is not transmitted in the bit stream
314. Signaling bits or flags are included in the bitstream 314 to
specify which MV residual was computed from the normalized motion
vector predictor, and are later used by the decoder to recover the
motion vector. These bits or flags are further described below.
[0097] Referring back to FIG. 3, the intra-predicted residuals 1004
and the inter-predicted residuals 1106 obtained from the spatial
(intra) or temporal (inter) prediction process are then transformed
by transform module 308 into the transform units (TUs) 802
described above. A TU 802 can be further split into smaller TUs
using the RQT decomposition described above with respect to FIG. 9.
In HEVC, generally 2 or 3 levels of decompositions are used and
authorized transform sizes are from 32.times.32, 16.times.16,
8.times.8 and 4.times.4. As described above, the transform is
derived according to a discrete cosine transform (DCT) or discrete
sine transform (DST).
[0098] The residual transformed coefficients are then quantized by
quantizer 310. Quantization plays a very important role in data
compression. In HEVC, quantization converts the high precision
transform coefficients into a finite number of possible values.
Although the quantization permits a great deal of compression,
quantization is a lossy operation, and the loss by quantization
cannot be recovered.
[0099] The coefficients of the quantized transformed residual are
then coded by means of an entropy coder 312 and then inserted into
the compressed bit stream 310 as a part of the useful data coding
the images of the AV information. Coding syntax elements may also
be coded using spatial dependencies between syntax elements to
increase the coding efficiency. HEVC offers context-adaptive binary
arithmetic coding (CABAC). Other forms or entropy or arithmetic
coding may also be used.
[0100] In order to calculate the predictors used above, the encoder
202 decodes already encoded PUs 702 using "decoding" loop 315,
which includes elements 316, 318, 320, 322, 328. This decoding loop
315 reconstructs the PUs and images from the quantized transformed
residuals.
[0101] The quantized transform residual coefficients E are provided
to dequantizer 316, which applies the inverse operation to that of
quantizer 310 to produce dequantized transform coefficients of the
residual PU (E') 708. The dequantized data 708 is then provided to
inverse transformer 318 which applies the inverse of the transform
applied by the transform module 308 to generate reconstructed
residual coefficients of the PU (e') 710.
[0102] The reconstructed coefficients of the residual PU 710 are
then added to the corresponding coefficients of the corresponding
predicted PU (x') 702' selected from the intra-predicted PU 1004
and the inter-predicted PU 1106 by selector 306. For example, if
the reconstructed residual comes from the "intra" coding process of
the spatial predictor 324, the "intra" predictor (x') is added to
this residual in order to recover a reconstructed PU (x'') 712
corresponding to the original PU 702 modified by the losses
resulting from a transformation, for example in this case the
quantization operations. If the residual 710 comes from an "inter"
coding process of the temporal predictor 330, the areas pointed to
by the current motion vectors (these areas belong to the reference
images stored in reference buffer 328 referred by the current image
indices) are merged then added to this decoded residual. In this
way the original PU 702 is modified by the losses resulting from
the quantization operations.
[0103] To the extent that the encoder 202 uses motion vector
prediction techniques analogous to the image prediction techniques
described above, the motion vector may be stored using motion
vector buffer 329 for use in temporally subsequent frames. As
further described below, a flag may be set and transferred in the
syntax to indicate that the motion vector for the currently decoded
frame should be used for at least the subsequently coded frame
instead of replacing the contents of the MV buffer 329 with the MV
for the current frame.
[0104] A loop filter 322 is applied to the reconstructed signal
(x'') 712 in order to reduce the effects created by heavy
quantization of the residuals obtained, and to improve the signal
quality. The loop filter 322 may comprise, for example, a
deblocking filter for smoothing borders between PUs to visually
attenuate high frequencies created by the coding process and a
linear filter that is applied after all of the PUs for an image
have been decoded to minimize the sum of the square difference
(SSD) with the original image. The linear filtering process is
performed on a frame by frame basis and uses several pixels around
the pixel to be filtered, and also uses spatial dependencies
between pixels of the frame. The linear filter coefficients may be
coded and transmitted in one header of the bitstream typically a
picture or slice header.
[0105] The filtered images, also known as reconstructed images, are
then stored as reference images from reference image buffer 328 in
order to allow the subsequent "Inter" predictions taking place
during the compression of the subsequent images of the current
video sequence.
Reference Image Syntax
[0106] As described above, to reduce errors and improve
compression, HEVC permits the use of several reference images for
the estimation and motion compensation of the current image. Given
a current PU 702 in a current picture, the collocated PU 1102 for a
particular slice resides in associated nearby
reference/non-reference picture. For example, in FIG. 12, the
collocated PU 1102 for current PU 702 in picture (i) resides in the
associated nearby reference picture (i-1). The best "inter" or
temporal predictors of the current PU 702 are selected in some of
the multiple reference/non-reference images, which may be based on
pictures temporally prior to or after the current picture in
display order (backwards and forward prediction, respectively).
[0107] For HEVC, the index to reference pictures is defined by
reference picture lists that are described in the slice syntax.
Forward prediction is defined by list.sub.--0 (RefPicList0), and
backward prediction is defined by list.sub.--1 (RefPicList1), and
both list 0 and list 1 can contain multiple reference pictures
prior to or/and later than the current picture in the display
order.
[0108] FIG. 13 illustrates an example of the use of the reference
picture lists. Consider pictures 0, 2, 4, 5, 6, 8 and 10 shown in
FIG. 13, wherein the numbers of each picture denote display order
and the current picture is picture 5. In this case, the
list.sub.--0 reference pictures with ascending reference picture
indices and starting with index equal to zero are 4, 2, 0, 6, 8 and
10, and the list.sub.--1 reference pictures with ascending
reference picture indices and starting with index equal to zero are
6, 8, 10, 4, 2, and 0. A slice that the motion compensated
prediction is restricted to the list.sub.--0 prediction is called a
predictive or P-slice. Collocated pictures are indicated by using
the collocated_ref_idx index in the HEVC. A slice for which the
motion-compensated prediction includes more than one reference
picture is a bi-predictive or B-slice. For B-slices, the motion
compensated prediction may include reference pictures from
list.sub.--1 prediction as well as list.sub.--0.
[0109] Hence, a collocated PU 1102 is disposed in a reference
picture specified in either list.sub.--0 or list.sub.--1. A flag
(collocated_from_l0_flag) is used to specify whether the collocated
partition should be derived from list.sub.--0 or list.sub.--1 for a
particular slice type. Each of the reference pictures is also
associated with a motion vector.
[0110] The storage and retrieval of reference pictures and related
motion vectors for the emerging HEVC standard is expressed in
paragraph 8.4.1.2.9 of Benjamin Bross, Woo Jin Han, Jens-Rainer
Ohm, Gary J. Sullivan, Thomas Wiegand, "WD4: Working Draft 4 of
High-Efficiency Video Coding," Joint Collaborative Team on Video
Coding QCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11,
JCTVC-F803_d5, 6th Meeting: Torino, IT, 14-22 Jul., 2011 (hereby
incorporated by reference herein).
[0111] According to the standard, if the slice_type is equal to B
and the collocated_from.sub.--10_flag is 0, the collocated_ref_idx
variable specifies the reference picture as the picture that
contains the co-located partition as specified by RefPicList1.
Otherwise (slice_type is equal to B and
collocated_from.sub.--10_flag is equal to 1 or slice_type is equal
to P), the collocated_ref_idx variable specifies the reference
picture as the picture that contains the collocated partition as
specified by RefPicList0.
[0112] FIG. 14 is a diagram illustrating processes performed by the
encoder 202 according to the aforementioned standard. Block 1402
determines whether the current picture is a reference picture for
another picture. If not, there is no need to store reference
picture or motion vector information. If the current picture is a
reference picture for another picture, block 1504 determines
whether the "another" picture is a P-type or a B-type picture. If
the picture is a P-type picture, processing is passed to blocks
1410, which set the colloc_from.sub.--10_flag to one and store the
reference picture and motion vector in list 0. If the "another
picture" is a B-type picture, block 1406 nonetheless directs
processing to blocks 1408 and 1410 if the desired reference picture
is to be stored in list 0, and to blocks 1412 and 1414 if the
desired reference picture and motion vector is to be stored in list
1. This decision may be based on whether it is desirable to select
reference pictures from a temporally preceding or succeeding
picture. Which of the multiple possible reference pictures is
selected is determined according to the collocated_ref_idx
index.
[0113] FIG. 15 depicts the use of a collocated_from.sub.--10_flag
by the decoder 220 in decoding a according to the previous HEVC
standard. Block 1502 determines if the current slice type being
computed is an intra or I-type. Such slices do not use temporally
nearby slices in the encoding/decoding process, and hence there is
no need to find a temporally nearby reference picture. If the slice
type is not I-type, block 1504 determines whether the slice is a
B-slice. If the slice is not a B-type, it is a P-type slice, and
the reference picture that contains the collocated partition is
found in list 0, according to the value of collocated_ref_idx. If
the slice is B-type, the collocated_from.sub.--10_flag determines
whether the reference picture is found in list 0 or list 1. As the
index indicates, the collocated picture is therefore defined as the
reference picture having the indicated collocated_ref_idx in either
list 0 or list 1, depending on the slice type (B-type or P-type)
and the value of the collocated_from.sub.--10_flag. In one
embodiment of HEVC, the first reference picture (the reference
picture having index [0] as shown in FIG. 13 is selected as the
collocated picture).
Baseline Picture Parameter Set Syntax
[0114] FIGS. 16A and 16B are diagrams presenting a baseline PPS Raw
Byte Sequence Payload (RBSP) syntax. Syntax for dealing with
extensions in the PPS are shown in FIG. 16B. Logic 1602 determines
if the media is to be coded/decoded including a first extension and
reads the appropriate signaling and data. Logic 1602 comprises
statements 1606-1616. Statement 1606 reads a pps_extensiona1_flag,
which indicates whether the first extension has been selected for
the coding/decoding process. In one embodiment, a logical value of
"1" indicates that the media is to be processed using the first
extension, and a logical value of "0" indicates that the media is
not to be processed using the first extension. Statement 1608 is a
conditional statement that directs execution of statements
1612-1614 depending upon the value of a (previously read)
transform_skip_enabled_flag. In particular, the illustrated logic
performs the operations shown in statements 1612-1614 if the
transform_skip_enabled_flag is a logical "1" or true.
[0115] Transform skipping is an extension that allows the DCT
transform of a TU to be skipped under certain circumstances.
Essentially, the DCT transform has the property that for media with
highly correlated signals, it results in outstanding energy
compaction. However, for media with highly uncorrelated signals
(e.g. media having a large amount of detail), the compaction
performance is much less. For some media, the DCT transform process
has so little compaction performance, the process is better skipped
for better processing performance. The transform_skip_enabled_flag
indicates when skipping the DCT transform of a TU is permitted.
This is described, for example, in "Early Termination of Transform
Skip Mode for High Efficiency Video Coding," by Do Kyung Lee, Miso
Park, Hyung-Do Kim and Je-Chang Jeong in the Proceedings of the
2014 International Conference on Communications, Signal Processing
and Computers, which is hereby incorporated by reference. If the
transform_skip_enabled_flag is a logical 1 (true), processing is
routed to statement 1612 and 1614. Otherwise, processing is routed
to statement 1618. Statement 1612 performs the operation of reading
a value log 2_transform_skip_max_size_minus2, which indicates the
maximum TU size that may be skipped (if the
transform_skip_enabled_flag indicates that performing the DCT
transform of the TU is permitted). Statement 1614 performs the
operation of reading a flag pps_extension2_flag indicating if a
further extension (extension2) is implemented.
[0116] Next, logic 1604 is performed. Logic 1604 includes
statements 1618-1622. Statement 1618 is a conditional statement
that routes processing to the logic of statements 1620 and 1622 if
the pps_extension2_flag is a logical 1. Statements 1620 and 1622
read additional pps_extension_data_flags while RBSP data
exists.
[0117] In the foregoing PPS design of HEVC range extension, the
pps_extension2_flag accounts for as yet unidentified extension
data. According to the logic described above, if
pps_extension1_flag is true, pps_extension2_flag is present. If
pps_extension1_flag is not true, pps_extension2_flag is not
present. If pps_extension2_flag is not present, pps_extension2_flag
is inferred to be equal to 0. If pps_extension2_flag is 0, there is
no additional extension_data.
[0118] This logical formulation always checks the value of
pps_extension2_flag for possible additional extension syntax
regardless of the status of pps_extension1_flag. However, if
pps_extension1_flag is 0, there is no need to check
pps_extension2_flag, because if pps_extension1_flag is 0,
pps_extension2_flag will not be present, and if pps_extension2_flag
is not present, it will inferred to be equal to 0, which indicates
that there is no further extension data.
[0119] FIG. 16C presents a modified PPS Raw Byte Sequence Payload
(RBSP) syntax. Logic 1602' is modified from logic 1602 and includes
statements 1606-1622. As before, statement 1606 implements logic
reading the pps_extension1_flag. Statement 1608 is a conditional
statement that commands the processing of logic associated with
statements 1610-1622 if the pps_extension1_flag is a logical 1 or
true, and otherwise skips these statements.
[0120] Statement 1610 is a conditional statement that commands the
operations of statements 1612-1614 be performed only if the
transform_skip_enabled_flag (described above) is a logical 1. Those
statements include, as before, a statement to read the value of the
log 2_transform_skip_max_size_minus.sub.--2, and the pps_extension
flag, as shown in statements 1612 and 1614. However, logic 1604
(statements 1616-1620) of FIG. 16B is now incorporated within the
conditional statement 1608, and is executed only if
pps_extension1_flag tests to a logical 1. This allows the logic of
statements 1610-1620 to be skipped if pps_extension1_flag tests to
a logical 0, thus saving execution time. While the foregoing is
illustrated with respect to a second extension to read additional
data that is only implicated if a first extension related to
transform skipping tests true, the first extension and second
extension may be any extensions that are non-independent (e.g. one
of the extension functions or operations are only implicated
depending on the status of another of the extension functions or
operations.
[0121] FIG. 16D is a flow chart illustrating exemplary operations
for decoding a sequence comprising a plurality of pictures that are
processed at least in part according to a picture parameter set. In
block 1630, a first extension flag (for example, the
pps_extension1_flag) that signals a first extension function is to
be performed in the processing of the sequence or the picture is
read. In block 1632, a determination is made as to whether the read
first flag has a first value, and if the flag does not have a first
value, processing is routed around the logic of blocks 1634 and
1636. In the embodiment illustrated in FIG. 16C, this is analogous
to logic of statement 1608 and 1622. Only if the read first flag
has the first value, processing is passed to block 1634, which
reads a second extension flag that signals a second extension
function in the processing of the sequence or picture, and block
1636 performs the second extension function according to the read
second extension flag. This is analogous to the logic of blocks
1614-1620.
[0122] In one embodiment, the first extension function is performed
according to the first extension flag after reading the first
extension flag and before reading the second extension flag. For
example, with respect to FIG. 16C, the log
2_transform_skip_max_size_minus2 value is read if the
pps_extension1_flag tests true before reading the
pps_extension2_flag. IN this case, the processed picture comprises
a plurality of TUs, and the processing sequence comprises DCT
transforming at least some of the TUs of the associated processed
picture, and skipping the DCT transforming process of other of the
plurality of transform units under certain circumstances, for
example, if the TU is greater in size than a maximum TU size (e.g.
4.times.4). In this case, the first extension function comprises
reading a value indicating the maximum permitted size of the TU for
which DCT transforming may be skipped.
[0123] As described above, the first extension function and the
second extension function may be functionally related. For example,
the second extension function may require receiving a result of the
first extension function, before the second extension function may
be completed. Or, the second extension function may be mutually
exclusive from the first extension function (e.g. either the first
extension function or the second extension function are to be
performed, but not both). Or, the second extension function may be
a function that would not be performed unless the first extension
function is also performed, hence the second extension function is
only implicated or performed in the processing sequence if the
first extension function is also performed. For example, a
computation may require an output or result from both the first
extension function and the second extension function, and hence,
existence of the first extension function necessarily implicates
the second extension function and vice-versa.
[0124] The foregoing operations are described with respect to a
decoding process, which can take place in either a the source
decoder 220 or an encoder 202, as a part of the encoding process.
The encoding process may also be expressed as comprising
determining if a slice of the one or more slices is an
inter-predicted slice according to slice type data, and if the
slice is an inter-predicted slice, configuring a first parameter in
the slice header associated with the slice to a value signaling
enablement of a state of weighted prediction of image data
associated with the slice.
Hardware Environment
[0125] FIG. 16 illustrates an exemplary processing system 1600 that
could be used to implement the embodiments of the invention. The
computer 1602 comprises a processor 1604 and a memory, such as
random access memory (RAM) 1606. The computer 1602 is operatively
coupled to a display 1622, which presents images such as windows to
the user on a graphical user interface 1618B. The computer 1602 may
be coupled to other devices, such as a keyboard 1614, a mouse
device 1616, a printer, etc. Of course, those skilled in the art
will recognize that any combination of the above components, or any
number of different components, peripherals, and other devices, may
be used with the computer 1602.
[0126] Generally, the computer 1602 operates under control of an
operating system 1608 stored in the memory 1606, and interfaces
with the user to accept inputs and commands and to present results
through a graphical user interface (GUI) module 1618A. Although the
GUI module 1618A is depicted as a separate module, the instructions
performing the GUI functions can be resident or distributed in the
operating system 1608, the computer program 1610, or implemented
with special purpose memory and processors. The computer 1602 also
implements a compiler 1612 which allows an application program 1610
written in a programming language such as COBOL, C++, FORTRAN, or
other language to be translated into processor 1604 readable code.
After completion, the application 1610 accesses and manipulates
data stored in the memory 1606 of the computer 1602 using the
relationships and logic that was generated using the compiler 1612.
The computer 1602 also optionally comprises an external
communication device such as a modem, satellite link, Ethernet
card, or other device for communicating with other computers.
[0127] In one embodiment, instructions implementing the operating
system 1608, the computer program 1610, and the compiler 1612 are
tangibly embodied in a computer-readable medium, e.g., data storage
device 1620, which could include one or more fixed or removable
data storage devices, such as a zip drive, floppy disc drive 1624,
hard drive, CD-ROM drive, tape drive, etc. Further, the operating
system 1608 and the computer program 1610 are comprised of
instructions which, when read and executed by the computer 1602,
causes the computer 1602 to perform the steps necessary to
implement and/or use the invention. Computer program 1610 and/or
operating instructions may also be tangibly embodied in memory 1606
and/or data communications devices 1630, thereby making a computer
program product or article of manufacture. As such, the terms
"article of manufacture," "program storage device" and "computer
program product" as used herein are intended to encompass a
computer program accessible from any computer readable device or
media.
[0128] The processing system 1600 may also be embodied in a
desktop, laptop, tablet, notebook computer, personal data assistant
(PDA), cellphone, smartphone, or any device with suitable
processing and memory capability. Further, the processing system
1600 may utilize special purpose hardware to perform some or all of
the foregoing functionality. For example the encoding and decoding
processes described above may be performed by a special purpose
processor and associated memory.
[0129] Those skilled in the art will recognize many modifications
may be made to this configuration without departing from the scope
of the present disclosure. For example, those skilled in the art
will recognize that any combination of the above components, or any
number of different components, peripherals, and other devices, may
be used. For example, particular functions described herein can be
performed by hardware modules, or a processor executing
instructions stored in the form of software or firmware. Further,
the functionality described herein can be combined in single
modules or expanded to be performed in multiple modules.
CONCLUSION
[0130] The foregoing description of the preferred embodiment has
been presented for the purposes of illustration and description. It
is not intended to be exhaustive or to limit the disclosure to the
precise form disclosed. Many modifications and variations are
possible in light of the above teaching. It is intended that the
scope of rights be limited not by this detailed description, but
rather by the claims appended hereto.
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