U.S. patent application number 13/493640 was filed with the patent office on 2012-12-13 for border pixel padding for intra prediction in video coding.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Peisong Chen, Ying Chen, Wei-Jung Chien, Marta Karczewicz, Xianglin Wang.
Application Number | 20120314767 13/493640 |
Document ID | / |
Family ID | 47293186 |
Filed Date | 2012-12-13 |
United States Patent
Application |
20120314767 |
Kind Code |
A1 |
Wang; Xianglin ; et
al. |
December 13, 2012 |
BORDER PIXEL PADDING FOR INTRA PREDICTION IN VIDEO CODING
Abstract
A video coder performs a padding operation that processes a set
of border pixels according to an order. The order starts at a
bottom-left border pixel and proceeds through the border pixels
sequentially to a top-right border pixel. When the padding
operation processes an unavailable border pixel, the padding
operation predicts a value of the unavailable border pixel based on
a value of a border pixel previously processed by the padding
operation. The video coder may generate an intra-predicted video
block based on the border pixels.
Inventors: |
Wang; Xianglin; (San Diego,
CA) ; Chien; Wei-Jung; (San Diego, CA) ;
Karczewicz; Marta; (San Diego, CA) ; Chen; Ying;
(San Diego, CA) ; Chen; Peisong; (San Diego,
CA) |
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
47293186 |
Appl. No.: |
13/493640 |
Filed: |
June 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61496504 |
Jun 13, 2011 |
|
|
|
61557361 |
Nov 8, 2011 |
|
|
|
61557845 |
Nov 9, 2011 |
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Current U.S.
Class: |
375/240.12 ;
375/E7.243 |
Current CPC
Class: |
H04N 19/105 20141101;
H04N 19/182 20141101; H04N 19/61 20141101; H04N 19/593
20141101 |
Class at
Publication: |
375/240.12 ;
375/E07.243 |
International
Class: |
H04N 7/32 20060101
H04N007/32 |
Claims
1. A method for coding video data, the method comprising:
performing a padding operation that processes a set of border
pixels according to an order that starts at a bottom-left border
pixel and proceeds through the border pixels sequentially to a
top-right border pixel, wherein when the padding operation
processes an unavailable border pixel, the padding operation
assigns a value to the unavailable border pixel based on a value of
a border pixel previously processed by the padding operation; and
generating an intra-predicted video block based on the border
pixels.
2. The method of claim 1, wherein performing the padding operation
comprises: determining whether a current border pixel is available;
and assigning to the current border pixel a value of a border pixel
that is immediately before the current border pixel according to
the order.
3. The method of claim 2, wherein determining whether the current
border pixel is available comprises determining that the current
border pixel is unavailable when the current border pixel is
associated with an inter-predicted CU and constrained
intra-prediction is enabled.
4. The method of claim 1, wherein performing the padding operation
comprises: determining whether the bottom-left border pixel is
available; and assigning a default value to the bottom-left border
pixel in response to determining that the bottom-left border pixel
is unavailable.
5. The method of claim 1, wherein performing the padding operation
comprises: determining whether the bottom-left border pixel is
available; and assigning a value of a next available border pixel
to the bottom-left border pixel in response to determining that the
bottom-left border pixel is unavailable.
6. The method of claim 1, wherein performing the padding operation
comprises: for x=-1, y=nS*2-2 . . . -1, substituting a value of
p[x, y+1] for a value of p[x, y] if p[x, y] is an unavailable
border pixel; and for x=0..nS*2-1, y-1, substituting a value of
p[x-1, y] for a value of p[x, y] if p[x, y] is an unavailable
border pixel, wherein nS is equal to a width or height of the
intra-predicted video block, p is a two-dimensional array of
samples, and p[0,0] is a top-left luma sample of the
intra-predicted video block.
7. The method of claim 1, wherein the method is performed during an
encoding process, the method further comprising generating encoded
video data based on the intra-predicted video block.
8. The method of claim 7, further comprising generating residual
data based at least in part on the intra-predicted video block.
9. The method of claim 1, wherein the method is performed during a
decoding process, the method further comprising generating decoded
video data based on the intra-predicted video block.
10. The method of claim 9, further comprising reconstructing a
decoded video block based at least in part on the intra-predicted
video block and a residual video block.
11. A video coding apparatus that comprises one or more processors
configured to: perform a padding operation that processes a set of
border pixels according to an order that starts at a bottom-left
border pixel and proceeds through the border pixels sequentially to
a top-right border pixel, wherein when the padding operation
processes an unavailable border pixel, the padding operation
assigns a value to the unavailable border pixel based on a value of
a border pixel previously processed by the padding operation; and
generate an intra-predicted video block based on the border
pixels.
12. The video coding apparatus of claim 11, wherein the one or more
processors are configured to perform the padding operation such
that the one or more processors: determine whether a current border
pixel is available; and assign to the current border pixel a value
of a border pixel that is immediately before the current border
pixel according to the order.
13. The video coding apparatus of claim 12, wherein the one or more
processors are configured to determine whether the current border
pixel is available at least in part by determining that the current
border pixel is unavailable when the current border pixel is
associated with an inter-predicted CU and constrained
intra-prediction is enabled.
14. The video coding apparatus of claim 11, wherein the one or more
processors are configured to perform the padding operation such
that the one or more processors: determine whether the bottom-left
border pixel is available; and assign a default value to the
bottom-left border pixel in response to determining that the
bottom-left border pixel is available.
15. The video coding apparatus of claim 11, wherein the one or more
processors are configured to perform the padding operation such
that the one or more processors: determining whether the
bottom-left border pixel is available; and assign a value of a next
available border pixel to the bottom-left border pixel in response
to determining that the bottom-left border pixel is
unavailable.
16. The video coding apparatus of claim 11, wherein the one or more
processors are configured to perform the padding operation such
that: for x=-1, y=nS*2-2 . . . -1, substituting a value of p[x,
y+1] for a value of p[x, y] if p[x, y] is an unavailable border
pixel; and for x=0..nS*2-1, y-1, substituting a value of p[x-1, y]
for a value of p[x, y] if p[x, y] is an unavailable border pixel,
wherein nS is equal to a width or height of the intra-predicted
video block, p is a two-dimensional array of samples, and p[0,0] is
a top-left luma sample of the intra-predicted video block.
17. The video coding apparatus of claim 11, wherein the video
coding apparatus comprises a video encoder and the one or more
processors are configured to generate encoded video data based on
the intra-predicted video block.
18. The video coding apparatus of claim 17, wherein the one or more
processors are configured to generate residual data based at least
in part on the intra-predicted video block.
19. The video coding apparatus of claim 11, wherein the video
coding apparatus comprises a video decoder and the one or more
processors are configured to generate decoded video data based on
the intra-predicted video block.
20. The video coding apparatus of claim 19, wherein the one or more
processors are configured to reconstruct a decoded video block
based on the intra-predicted video block and a residual video
block.
21. A video coding apparatus comprising: means for performing a
padding operation that processes a set of border pixels according
to an order that starts at a bottom-left border pixel and proceeds
through the border pixels sequentially to a top-right border pixel,
wherein when the padding operation processes an unavailable border
pixel, the padding operation assigns a value to the unavailable
border pixel based on a value of a border pixel previously
processed by the padding operation; and means for generating an
intra-predicted video block based on the border pixels.
22. The video coding apparatus of claim 21, wherein the means for
performing the padding operation comprises: means for determining
whether a current border pixel is available; and means for
assigning to the current border pixel a value of a border pixel
that is immediately before the current border pixel according to
the order.
23. The video coding apparatus of claim 22, wherein the means for
determining whether the current border pixel is available comprises
means for determining that the current border pixel is unavailable
when the current border pixel is associated with an inter-predicted
CU and constrained intra-prediction is enabled.
24. A computer program product that comprises one or more
computer-readable storage media that store computer-executable
instructions that, when executed, cause one or more processors to:
perform a padding operation that processes a set of border pixels
according to an order that starts at a bottom-left border pixel and
proceeds through the border pixels sequentially to a top-right
border pixel, wherein when the padding operation processes an
unavailable border pixel, the padding operation assigns a value to
the unavailable border pixel based on a value of a pixel previously
processed by the padding operation; and generate an intra-predicted
video block based on the border pixels.
25. The computer program product of claim 24, wherein the
computer-executable instructions cause the one or more processors
to: determine whether a current border pixel is available; and
assign to the current border pixel a value of a border pixel that
is immediately before the current border pixel according to the
order.
26. The computer program product of claim 25, wherein the
computer-executable instructions cause the one or more processors
to determine that the current border pixel is unavailable when the
current border pixel is associated with an inter-predicted CU and
constrained intra-prediction is enabled.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/496,504, filed Jun. 13, 2011, U.S. Provisional
Application No. 61/557,361, filed Nov. 8, 2011, and U.S.
Provisional Application No. 61/557,845, filed Nov. 9, 2011, the
entire content each of which is hereby incorporated by
reference.
TECHNICAL FIELD
[0002] This disclosure relates to video coding and, more
particularly, intra prediction of video data.
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, digital cameras,
digital recording devices, digital media players, video gaming
devices, video game consoles, cellular or satellite radio
telephones, video teleconferencing 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, to transmit, receive
and store digital video information more efficiently.
[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 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.
SUMMARY
[0005] In general, this disclosure describes techniques for padding
border pixels for intra prediction in video coding. In accordance
with the techniques of this disclosure, the video coder may perform
a padding operation that assigns values to unavailable border
pixels. The padding operation may process the border pixels
according to an order that starts at a bottom-left border pixel and
proceeds through the border pixels sequentially to a top-right
border pixel. When the padding operation processes an unavailable
border pixel, the padding operation may assign a value to the
unavailable border pixel based on a value of a border pixel
previously processed by the padding operation. The video coder may
generate an intra-predicted video block based on the border
pixels.
[0006] In one aspect, this disclosure describes a method for coding
video data. The method comprises performing a padding operation
that processes a set of border pixels according to an order that
starts at a bottom-left border pixel and proceeds through the
border pixels sequentially to a top-right border pixel. When the
padding operation processes an unavailable border pixel, the
padding operation assigns a value to the unavailable border pixel
based on a value of a border pixel previously processed by the
padding operation. The method also comprises generating an
intra-predicted video block based on the border pixels.
[0007] This disclosure also describes a video coding apparatus that
comprises one or more processors configured to perform a padding
operation that processes a set of border pixels according to an
order that starts at a bottom-left border pixel and proceeds
through the border pixels sequentially to a top-right border pixel.
When the padding operation processes an unavailable border pixel,
the padding operation assigns a value to the unavailable border
pixel based on a value of a border pixel previously processed by
the padding operation. The one or more processors are also
configured to generate an intra-predicted video block based on the
border pixels.
[0008] In addition, this disclosure describes a video coding
apparatus comprising means for performing a padding operation that
processes a set of border pixels according to an order that starts
at a bottom-left border pixel and proceeds through the border
pixels sequentially to a top-right border pixel. When the padding
operation processes an unavailable border pixel, the padding
operation assigns a value to the unavailable border pixel based on
a value of a border pixel previously processed by the padding
operation. The video coding apparatus also comprises means for
generating an intra-predicted video block based on the border
pixels.
[0009] This disclosure also describes a computer program product
that comprises one or more computer-readable storage media that
store computer-executable instructions that, when executed, cause
one or more processors to perform a padding operation that
processes a set of border pixels according to an order that starts
at a bottom-left border pixel and proceeds through the border
pixels sequentially to a top-right border pixel. When the padding
operation processes an unavailable border pixel, the padding
operation assigns a value to the unavailable border pixel based on
a value of a pixel previously processed by the padding operation.
The instructions also cause the one or more processors to generate
an intra-predicted video block based on the border pixels.
[0010] 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
[0011] FIG. 1 is a block diagram illustrating an example video
coding system that may implement the techniques of this
disclosure.
[0012] FIG. 2 is a conceptual diagram that illustrates an example
video block and a set of border pixels associated with the video
block.
[0013] FIG. 3A is a conceptual diagram that illustrates example
intra-prediction modes in High Efficiency Video Coding.
[0014] FIG. 3B is a conceptual diagram that indicates another
example assignment of numbers to different intra prediction
modes.
[0015] FIG. 3C is a conceptual diagram that illustrates example
intra-prediction modes in H.264/AVC.
[0016] FIG. 4 is a block diagram illustrating an example video
encoder that may implement the techniques of this disclosure.
[0017] FIG. 5 is a block diagram illustrating an example video
decoder that may implement the techniques of this disclosure.
[0018] FIG. 6 is a flowchart that illustrates an example
intra-prediction operation.
[0019] FIG. 7 is a flowchart that illustrates an example padding
operation.
[0020] FIG. 8 is a conceptual diagram that illustrates an order in
which the example padding operation of FIG. 7 proceeds through
border pixels.
[0021] FIG. 9 is a flowchart that illustrates another example
padding operation.
[0022] FIG. 10 is a conceptual diagram that illustrates an example
order in which the padding operation of FIG. 9 proceeds through
border pixels.
[0023] FIG. 11 is a flowchart that illustrates another example
padding operation.
[0024] FIG. 12 is a conceptual diagram that illustrates an example
order in which the padding operation of FIG. 11 proceeds through
border pixels.
[0025] FIG. 13 is a flowchart that illustrates an example operation
for determining whether a border pixel is available.
DETAILED DESCRIPTION
[0026] The attached drawings illustrate examples. Elements
indicated by reference numbers in the attached drawings correspond
to elements indicated by like reference numbers in the following
description. In this disclosure, elements having names that start
with ordinal words (e.g., "first," "second," "third," and so on) do
not necessarily imply that the elements have a particular order.
Rather, such ordinal words are merely used to refer to different
elements of a same or similar type.
[0027] A video coder may generate an intra-predicted video block
based on a set of pixels that border the video block on the top and
left sides of the video block. The border pixels on the left side
of the video block may extend below the bottom row of pixels of the
video block and the border pixels on the top side of the video
block may extend to the right of the rightmost column of pixels of
the video block.
[0028] In some instances, one or more of the border pixels may be
unavailable. Accordingly, the video coder may perform a padding
operation that assigns values to unavailable border pixels. The
padding operation may process the border pixels according to an
order that starts at a bottom-left border pixel and proceeds
through the border pixels sequentially to a top-right border pixel.
When the padding operation processes an unavailable border pixel,
the padding operation may assign a value to the unavailable border
pixel based on a value of a border pixel previously processed by
the padding operation. After performing the padding operation, the
video coder may generate the intra-predicted video block based on
the border pixels. If the video coder is a video encoder, the video
coder may generate encoded video data based on the intra-predicted
video block. For instance, the video encoder may generate residual
data based at least in part on the intra-predicted video block. If
the video coder is a video decoder, the video coder may generate
decoded video data based on the intra-predicted video block. For
instance, the video decoder may reconstruct a decoded video block
based at least in part on the intra-predicted video block and a
residual video block.
[0029] FIG. 1 is a block diagram that illustrates an example video
coding system 10 that may utilize the techniques of this
disclosure. As used described herein, the term "video coder" refers
generically to both video encoders, video decoders, and combined
encoder-decoders (CODECs). In this disclosure, the terms "video
coding" or "coding" may refer generically to video encoding and
video decoding. The terms coder, encoder, decoder and CODEC may all
refer to specific machines designed for the coding (encoding and/or
decoding) of video data consistent with this disclosure. A device
that performs video coding may be referred to as a video coding
device or apparatus.
[0030] As shown in FIG. 1, video coding system 10 includes a source
device 12 and a destination device 14. Source device 12 generates
encoded video data. Destination device 14 may decode the encoded
video data generated by source device 12. Source device 12 and
destination device 14 may comprise a wide range of devices,
including desktop computers, notebook (e.g., laptop) computers,
tablet computers, set-top boxes, telephone handsets such as
so-called "smart" phones, so-called "smart" pads, televisions,
cameras, display devices, digital media players, video gaming
consoles, in-car computers, or the like. In some examples, source
device 12 and destination device 14 may be equipped for wireless
communication.
[0031] Destination device 14 may receive encoded video data from
source device 12 via a channel 16. Channel 16 may comprise any type
of medium or device capable of moving the encoded video data from
source device 12 to destination device 14. In one example, channel
16 may comprise a communication medium that enables source device
12 to transmit encoded video data directly to destination device 14
in real-time. In this example, source device 12 may modulate the
encoded video data according to a communication standard, such as a
wireless communication protocol, and may transmit the modulated
video data to destination device 14. The communication medium may
comprise a wireless or wired communication medium, such as a radio
frequency (RF) spectrum or one or more physical transmission lines.
The communication medium 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. The communication medium may include
routers, switches, base stations, or other equipment that
facilitates communication from source device 12 to destination
device 14.
[0032] In another example, channel 16 may correspond to a storage
medium that stores the encoded video data generated by source
device 12. In this example, destination device 14 may access the
storage medium via disk access or card access. The storage medium
may include a variety of locally accessed data storage media such
as Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable
digital storage media for storing encoded video data. In a further
example, channel 16 may include a file server or another
intermediate storage device that stores the encoded video generated
by source device 12. In this example, destination device 14 may
access encoded video data stored at the file server or another
intermediate storage device via streaming or download. The file
server may be a type of server capable of storing encoded video
data and transmitting the encoded video data to destination device
14. Example file servers include web servers (e.g., for a website),
FTP servers, network attached storage (NAS) devices, and local disk
drives. Destination device 14 may access the encoded video data
through a standard data connection, such as an Internet connection.
Example types of data connections may include wireless channels
(e.g., Wi-Fi connections), wired connections (e.g., DSL, cable
modem, etc.), or combinations of both that are suitable for
accessing encoded video data stored on a file server. The
transmission of encoded video data from the file server may be a
streaming transmission, a download transmission, or a combination
of both.
[0033] The techniques of this disclosure are not limited to
wireless applications or settings. The techniques may be applied to
video coding in support of any of a variety of multimedia
applications, such as over-the-air television broadcasts, cable
television transmissions, satellite television transmissions,
streaming video transmissions, e.g., via the Internet, encoding of
digital video for storage on a data storage medium, decoding of
digital video stored on a data storage medium, or other
applications. In some examples, video coding system 10 may be
configured to support one-way or two-way video transmission to
support applications such as video streaming, video playback, video
broadcasting, and/or video telephony.
[0034] In the example of FIG. 1, source device 12 includes a video
source 18, a video encoder 20, and an output interface 22. In some
cases, output interface 22 may include a modulator/demodulator
(modem) and/or a transmitter. Video source 18 may include a source
such as a video capture device, e.g., a video camera, a video
archive containing previously captured video data, a video feed
interface to receive video data from a video content provider,
and/or a computer graphics system for generating video data, or a
combination of such sources.
[0035] Video encoder 20 may encode video data. Output interface 22
may directly transmit the encoded video data to destination device
14. Alternatively, output interface 22 may store the encoded video
data onto a storage medium or a file server for later access by
destination device 14 for decoding and/or playback.
[0036] In the example of FIG. 1, destination device 14 includes an
input interface 28, a video decoder 30, and a display device 32. In
some cases, input interface 28 may include a receiver and/or a
modem. Input interface 28 of destination device 14 receives encoded
video data over channel 16. The encoded video data may include a
variety of syntax elements that represent the video data.
[0037] Display device 32 may be integrated with or may be external
to destination device 14. In other examples, destination device 14
may be a display device. In general, display device 32 displays
decoded video data to a user. Display device 32 may comprise any of
a variety of display devices such as a liquid crystal display
(LCD), a plasma display, an organic light emitting diode (OLED)
display, or another type of display device.
[0038] Video encoder 20 and video decoder 30 may operate according
to a video compression standard, such as the High Efficiency Video
Coding (HEVC) standard presently under development, and may conform
to a HEVC Test Model (HM). Alternatively, video encoder 20 and
video decoder 30 may operate according to other proprietary or
industry standards, such as the ITU-T H.264 standard, alternatively
referred to as MPEG-4, Part 10, Advanced Video Coding (AVC), or
extensions of such standards. The techniques of this disclosure,
however, are not limited to any particular coding standard. Other
example video compression standards include MPEG-2 and ITU-T
H.263.
[0039] Although not shown in the example of FIG. 1, 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. In some
examples, the MUX-DEMUX units may conform to the ITU H.223
multiplexer protocol, or other protocols such as the user datagram
protocol (UDP).
[0040] Again, FIG. 1 is merely an example and the techniques of
this disclosure may apply to video coding settings (e.g., video
encoding or video decoding) that do not necessarily include any
data communication between encoding and decoding devices. In many
examples, video encoding and video decoding is performed by devices
that do not communicate with one another, but store encoded video
data to memory and/or retrieve and decode encoded video data from
memory.
[0041] Video encoder 20 and video decoder 30 each may be
implemented using various types of circuitry, such as one or more
microprocessors, digital signal processors (DSPs), application
specific integrated circuits (ASICs), field programmable gate
arrays (FPGAs), discrete logic, hardware, or any combinations
thereof. In some instances, video encoder 20 and video decoder 30
may be at least partially implemented in software. When video
encoder 20 and/or video decoder 30 are implemented partially in
software, a device may store instructions for the software in a
suitable, non-transitory computer-readable storage medium and may
execute the instructions in hardware using one or more processors
to perform the techniques of this disclosure. 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 device.
[0042] As mentioned briefly above, video encoder 20 encodes video
data. The video data may comprise one or more pictures. Each of the
pictures is a still image forming part of a video. In some
instances, a picture may be referred to as a video "frame." When
video encoder 20 encodes the video data, video encoder 20 may
generate a bitstream. The bitstream may include a sequence of bits
that form a coded representation of the video data.
[0043] To generate the bitstream, video encoder 20 may perform
encoding operations on each picture in the video data. When video
encoder 20 performs encoding operations on the pictures, video
encoder 20 may generate a series of coded pictures and associated
data. A coded picture is a coded representation of a picture. The
associated data may include sequence parameter sets, picture
parameter sets, adaptation parameter sets, and other syntax
structures. A sequence parameter set (SPS) may contain parameters
applicable to zero or more sequences of pictures. A picture
parameter set (PPS) may contain parameters applicable to zero or
more pictures. An adaptation parameter set (APS) may contain
parameters applicable to zero or more pictures. Parameters in the
PPS may be fixed for a set of pictures, whereas parameters in
different adaptation parameter sets may be applicable to different
pictures in the set of pictures.
[0044] To generate a coded picture, video encoder 20 may partition
a picture into equally-sized non-overlapping video blocks. Each of
the video blocks is associated with a treeblock. In some instances,
a treeblock may also be referred to as a largest coding unit (LCU).
The treeblocks of HEVC may be broadly analogous to the macroblocks
of previous standards, such as H.264/AVC. However, a treeblock is
not necessarily limited to a particular size and may include one or
more coding units (CUs). Video encoder 20 may use quadtree
partitioning to partition the video blocks of treeblocks into video
blocks associated with CUs, hence the name "treeblocks."
[0045] In some examples, video encoder 20 may partition a picture
into a plurality of slices. Each of the slices may include an
integer number of CUs. In some instances, a slice comprises an
integer number of treeblocks. In other instances, a boundary of a
slice may be within a treeblock.
[0046] As part of performing an encoding operation on a picture,
video encoder 20 may perform encoding operations on each slice of
the picture. When video encoder 20 performs an encoding operation
on a slice, video encoder 20 may generate encoded data associated
with the slice. The encoded data associated with the slice may be
referred to as a "coded slice."
[0047] To generate a coded slice, video encoder 20 may perform
encoding operations on each treeblock in a slice. When video
encoder 20 performs an encoding operation on a treeblock, video
encoder 20 may generate a coded treeblock. The coded treeblock may
comprise data representing an encoded version of the treeblock.
[0048] To generate a coded treeblock, video encoder 20 may
recursively perform quadtree partitioning on the video block of the
treeblock to divide the video block into progressively smaller
video blocks. Each of the smaller video blocks may be associated
with a different CU. For example, video encoder 20 may partition
the video block of a treeblock into four equally-sized sub-blocks,
partition one or more of the sub-blocks into four equally-sized
sub-sub-blocks, and so on. One or more syntax elements in the
bitstream may indicate a maximum number of times video encoder 20
may partition the video block of a treeblock. A video block of a CU
may be square in shape. The size of the video block of a CU (i.e.,
the size of the CU) may range from 8.times.8 pixels up to the size
of a video block of a treeblock (i.e., the size of the treeblock)
with a maximum of 64.times.64 pixels or greater.
[0049] Video encoder 20 may perform encoding operations on each
non-partitioned CU of a treeblock. A non-partitioned CU is a CU
whose video block is not partitioned into video blocks for other
CUs. As part of performing an encoding operation on a
non-partitioned CU, video encoder 20 may generate one or more
prediction units (PUs) for the CU. Each of the PUs of the CU may be
associated with a different video block within the video block of
the CU. Video encoder 20 may generate a predicted video block for
each PU of the CU. The predicted video block of a PU may be a block
of samples. In this disclosure, the term "sample" may refer to a
brightness (luminance) or color (chrominance) of a pixel. Video
encoder 20 may use intra prediction or inter prediction to generate
the predicted video block for a PU.
[0050] When video encoder 20 uses intra prediction to generate the
predicted video block of a PU, video encoder 20 may generate the
predicted video block of the PU based on samples of the picture
associated with the PU. If video encoder 20 uses intra prediction
to generate predicted video blocks of the PUs of a CU, the CU is an
intra-predicted CU.
[0051] When video encoder 20 uses inter prediction to generate the
predicted video block of the PU, video encoder 20 may generate the
predicted video block of the PU based on values of pictures other
than the picture associated with the PU. In other words, video
encoder 20 may generate the predicted video block of the PU based
on samples in one or more reference pictures. In addition, when
video encoder 20 uses inter prediction to generate a predicted
video block for a PU, video encoder 20 may generate motion
information for the PU. The motion information for a PU may
indicate a portion of a reference picture that corresponds to the
video block of the PU. In other words, the motion information for a
PU may indicate a "reference sample" for the PU. Video encoder 20
may generate the predicted video block for the PU based on the
portions of the reference pictures that are indicated by the motion
information for the PU. If video encoder 20 uses inter prediction
to generate predicted video blocks for the PUs of a CU, the CU is
an inter-predicted CU.
[0052] After video encoder 20 generates predicted video blocks for
one or more PUs of a CU, video encoder 20 may generate residual
data for the CU based on the predicted video blocks for the PUs of
the CU. The residual data for the CU may indicate differences
between samples in the predicted video blocks for the PUs of the CU
and the original video block of the CU.
[0053] Furthermore, as part of performing an encoding operation on
a non-partitioned CU, video encoder 20 may perform recursive
quadtree partitioning on the residual data of the CU to partition
the residual data of the CU into one or more blocks of residual
data (i.e., residual video blocks) associated with transform units
(TUs) of the CU. Each TU of a CU may be associated with a different
residual video block. Video coder 20 may perform transform
operations on each TU of the CU.
[0054] When video encoder 20 performs the transform operation on a
TU, video encoder 20 may apply one or more transforms to a residual
video block associated with the TU to generate one or more
transform coefficient blocks (i.e., blocks of transform
coefficients) associated with the TU. Conceptually, a transform
coefficient block may be a two-dimensional (2D) matrix of transform
coefficients.
[0055] After generating a transform coefficient block, video
encoder 20 may perform a quantization operation on the transform
coefficient block. Quantization generally refers to a process in
which transform coefficients are quantized to possibly reduce the
amount of data used to represent the transform coefficients,
providing further compression. Quantization may reduce the bit
depth associated with some or all of the transform coefficients.
For example, an n-bit transform coefficient may be rounded down to
an m-bit transform coefficient during quantization, where n is
greater than m.
[0056] Video encoder 20 may associate each CU or a number of CUs
with a quantization parameter (QP) value. The QP value associated
with a CU may determine how video encoder 20 quantizes transform
coefficient blocks associated with the CU or the number of CUs.
Video encoder 20 may adjust the degree of quantization applied to
the transform coefficient blocks associated with a CU by adjusting
the QP value associated with the CU.
[0057] After video encoder 20 quantizes a transform coefficient
block, video encoder 20 may scan the quantized transform
coefficients to produce a one-dimensional vector of transform
coefficient levels. Video encoder 20 may entropy encode the
one-dimensional vector. Video encoder 20 may also entropy encode
other syntax elements associated with the video data.
[0058] The bitstream generated by video encoder 20 may include a
series of Network Abstraction Layer (NAL) units. Each of the NAL
units may be a syntax structure containing an indication of a type
of data in the NAL unit and bytes containing the data. For example,
a NAL unit may contain data representing a sequence parameter set,
a picture parameter set, a coded slice, supplemental enhancement
information (SEI), an access unit delimiter, filler data, or
another type of data. The data in a NAL unit may include entropy
encoded syntax structures, such as entropy-encoded transform
coefficient blocks, motion information, and so on.
[0059] Video decoder 30 may receive the bitstream generated by
video encoder 20. The bitstream may include an encoded
representation of the video data encoded by video encoder 20. When
video decoder 30 receives the bitstream, video decoder 30 may
perform a parsing operation on the bitstream. When video decoder 30
performs the parsing operation, video decoder 30 may extract syntax
elements from the bitstream. Video decoder 30 may reconstruct the
pictures of the video data based on the syntax elements extracted
from the bitstream. The process to reconstruct the video data based
on the syntax elements may be generally reciprocal to the process
performed by video encoder 20 to generate the syntax elements.
[0060] After video decoder 30 extracts the syntax elements
associated with a CU, video decoder 30 may generate intra-predicted
or inter-predicted video blocks for the PUs of the CU based on the
syntax elements. In addition, video decoder 30 may inverse quantize
transform coefficient blocks associated with TUs of the CU. Video
decoder 30 may perform inverse transforms on the transform
coefficient blocks to reconstruct residual video blocks associated
with the TUs of the CU. After generating the predicted video blocks
and reconstructing the residual video blocks, video decoder 30 may
reconstruct the video block of the CU based on the predicted video
blocks and the residual video blocks. In this way, video decoder 30
may determine the video blocks of CUs based on the syntax elements
in the bitstream.
[0061] As described briefly above, a video coder, such as video
encoder 20 or video decoder 30, may use intra-prediction to
generate a predicted video block for a PU. For ease of explanation,
this disclosure may refer to a predicted video block generated
using intra-prediction as an intra-predicted video block. When the
video coder generates an intra-predicted video block for a PU, the
video coder may assign the values of various border pixels to
pixels in the intra-predicted video block.
[0062] FIG. 2 is a conceptual diagram that illustrates an example
video block 50 and a set of border pixels associated with video
block 50. Video block 50 may be associated with a PU of a CU that a
video coder is currently coding. In the example of FIG. 2, video
block 50 consists of sixteen pixels labeled a-p. In the example of
FIG. 2, the border pixels are labeled A-R. Other video blocks may
be larger or smaller than video block 50. In general, a video block
may be associated with 2*w+1 border pixels above the video block
and 2*h+1 border pixels to the left of the video block, where w is
the width and h is the height of the video block.
[0063] The border pixels above a video block (e.g., video block 50)
may form a top predictor. In other words, the top predictor may be
an array of reference samples corresponding to a row of samples
lying above the video block. If the top-left pixel of the video
block has coordinates (x, y) and the size of the video block is
N.times.N, the samples with coordinates (x+i, y-1), where i ranges
from -1 through 2N, form the top predictor. The border pixels to
the left of the video block form a left predictor. In other words,
the left predictor may be an array of reference samples
corresponding to a column of samples lying to the left of the video
block. If the top-left pixel of the video block has coordinates (x,
y) and the size of the video block is N.times.N, the samples with
coordinates (x-1, y+j), where j ranges from -1 through 2N form the
left predictor.
[0064] FIG. 3A is a conceptual diagram that illustrates example
intra-prediction modes in HEVC. In the example of FIG. 3A,
intra-prediction modes 1, 2, and 4-33 correspond to different
directions from which a video coder may extend border pixels to
generate an intra-predicted video block. For example, when the
video coder uses intra-prediction mode 1, the video coder may
generate an intra-predicted video block by extending the values of
border pixels vertically downward. In this example, the video coder
may use intra-prediction mode 1 to generate video block 50 (FIG. 2)
by assigning the value of border pixel A to pixels a, e, i, and m,
by assigning the value border pixel B to pixels b, f, j, and n, by
assigning the value of border pixel C to pixels c, g, k, and o, and
by assigning the value of border pixel D to pixels d, h, l, and
p.
[0065] Mode 0 may refer to a planar mode. The video coder may use
to following formula to generate an intra-predicted video block
using planar mode:
predSamples[x,
y]=((nS-1-x)*p[-1,y]+(x+1)*p[nS,-1]+(nS-1-y)*p[x,-1]+(y+1)*p[-1,nS]+nS)&g-
t;>(k+1)
with x, y=0..nS-1 where k=Log 2(nS) [0066] In the formula above,
predSamples[x, y] is an array of intra-predicted samples, nS
indicates a size of the predicted video block, and p[x, y] is an
array of neighboring samples.
[0067] Mode 3 may refer to a DC mode. To generate an
intra-predicted video block using the DC mode, the video coder may
first calculate a value DCVal using the following formula:
DCVal = ( x ' = 0 nS - 1 p [ x ' , - 1 ] + y ' = 0 nS - 1 p [ - 1 ,
y ' ] + nS ) >> ( k + 1 ) , with ##EQU00001## x , y = 0 nS -
1 ##EQU00001.2##
If a chrominance index (cIdx) of a current block is equal to 0, the
following applies.
predSamples[0, 0]=(1*p[-1, 0]+2*DCVal+1*p[0,-1]+2)>>2
predSamples[x, 0]=(1*p[x,-1]+3*DCVal+2)>>2, with
x=1..nS-1
predSamples[0, y]=(1*p[-1, y]+3*DCVal+2)>>2, with
y=1..nS-1
predSamples[x, y]=DCVal, with x, y=1..nS-1
Otherwise, the prediction samples predSamples[x, y] are derived
as
predSamples[x, y]=DCVal, with x, y=0..nS-1
In the formulas above, predSamples[x, y] is an array of
intra-predicted samples, nS indicates a size of the predicted video
block, and p[x, y] is an array of neighboring samples.
[0068] In another example, when the video coder uses
intra-prediction mode 10, the video coder may generate an
intra-predicted video block by extending the values of border
pixels diagonally from bottom-left to top-right. In the example of
FIG. 2, the video coder may use intra-prediction mode 10 to
generate video block 50 by assigning the value of border pixel J to
pixel a, by assigning the value of border pixel K to pixels e and
b, by assigning the value of border pixel L to pixels i, f, and c,
by assigning the value of border pixel M to pixels m, j, g, and d,
by assigning the value of border pixel N to pixels n, k, and h, by
assigning the value of border pixel O to pixels o and l, and by
assigning the value of border pixel P to pixel p.
[0069] In other examples, the video coder may use different numbers
to indicate intra-prediction modes. For instance, FIG. 3B is a
conceptual diagram that indicates another assignment of numbers to
different intra prediction modes.
[0070] FIG. 3C is a conceptual diagram that illustrates example
intra-prediction modes in H.264/AVC. There may be fewer available
intra-prediction modes in H.264/AVC.
[0071] In some instances, one or more of the border pixels
associated with an intra-predicted video block are unavailable. The
set of border pixels associated with an intra-predicted video block
may include the border pixels that the video coder may use to
generate the intra-predicted video block. When a border pixel is
unavailable, the video coder may be unable to access the value of
the border pixel. Accordingly, the video coder may be unable to use
the value of the border pixel to generate an intra-predicted video
block.
[0072] A border pixel may be unavailable for a variety of reasons.
For example, a border pixel may be unavailable if the border pixel
is outside the border of the current picture (i.e., the picture
that the video coder is currently coding). In another example, a
border pixel may be unavailable if the border pixel is outside the
border of a current slice or tile (i.e., the slice or tile that the
video coder is current coding) and cross-slice/tile prediction is
disallowed. In another example, a border pixel may be unavailable
if the border pixel is associated with an inter-predicted CU and
constrained intra-prediction is enabled for the current
picture.
[0073] Because one or more border pixels may be unavailable, the
video coder may perform a padding operation that assigns values to
unavailable border pixels. After the video coder performs the
padding operation, the video coder may use the available values of
the available border pixels and the assigned values of the
unavailable border pixels to generate an intra-predicted video
block.
[0074] Different video coders may assign values to unavailable
border pixels in various ways. For example, the video coder may
perform a padding operation that scans through the border pixels
from a bottom-left border pixel (e.g., border pixel P in FIG. 2) to
a corner pixel (e.g., border pixel R in FIG. 2) to a top-right
border pixel (e.g., border pixel H in FIG. 2). In this example,
when the video coder reaches an unavailable border pixel, the video
coder may scan forward to until the video coder reaches a next
available border pixel. Upon identifying the available border
pixel, the padding operation may assign a value to the unavailable
border pixel based on the values of the next available pixel and a
previous available border pixel.
[0075] In the example padding operation described above, if there
is no previous available border pixel, the video coder may scan
ahead to find the first available border pixel and then assign the
value of the first available border pixel to each unavailable
border pixel prior to the first available border pixel. In other
words, P.sub.pad=P.sub.next, where P.sub.pad is the value assigned
to each unavailable border pixel prior to the first available
border pixel and P.sub.next is the value of the next available
border pixel. If there is no next available border pixel, the video
coder may extrapolate the value of the unavailable border pixel
from the value of the last available border pixel. In other words,
P.sub.pad=P.sub.pre, where P.sub.pad is the value of each
unavailable border pixel after the last available border pixel and
P.sub.pre is the value of the last available border pixel. If no
border pixels of P.sub.pre and P.sub.next are available, the video
coder may assign a default value to the border pixels.
[0076] Assigning values to unavailable border pixels in the manner
described in the previous paragraphs may have several
disadvantages. For example, assigning values to each unavailable
border pixel in this manner may require the video coder to perform
several memory read operations to scan forward to find the next
available border pixel. Consequently, the padding operation
described above may require a jumpy style memory access. For
instance, once the video coder locates a next available border
pixel, the video coder may assign a value P.sub.pad to an
unavailable border pixel. Then, the video coder may assign the
value P.sub.pad to each border pixel from a current border pixel
until the next available border pixel, which may require memory
accesses starting from the current border pixel again. Such a back
and forth style memory access pattern may not be desirable. Memory
access operations may be time consuming and power intensive,
especially when memory is accessed in a random manner in terms of
data location.
[0077] In accordance with the techniques of this disclosure, the
video coder may perform a padding operation that processes a set of
border pixels according to an order that starts at a bottom-left
border pixel (e.g., border pixel P in FIG. 2) and proceeds through
the border pixels sequentially to a top-right border pixel (e.g.,
border pixel H in FIG. 2). When the padding operation processes an
unavailable border pixel, the padding operation assigns a value to
the unavailable border pixel based on a value of a border pixel
previously processed by the padding operation. In this way, the
video coder does not need to scan ahead to find the next available
border pixel. At the same time, this padding operation may have
little impact on coding efficiency of video data. Because the video
coder may use a more regular and consistent memory access pattern,
the complexity of the video coder may be reduced and performance of
the video coder may be improved relative to video coders that
implement other techniques.
[0078] FIG. 4 is a block diagram that illustrates an example video
encoder 20 that is configured to implement the techniques of this
disclosure. FIG. 4 is provided for purposes of explanation and
should not be considered limiting of the techniques as broadly
exemplified and described in this disclosure. For purposes of
explanation, this disclosure describes video encoder 20 in the
context of HEVC coding. However, the techniques of this disclosure
may be applicable to other coding standards or methods.
[0079] In the example of FIG. 4, video encoder 20 includes a
plurality of functional components. The functional components of
video encoder 20 include a prediction module 100, a residual
generation module 102, a transform module 104, a quantization
module 106, an inverse quantization module 108, an inverse
transform module 110, a reconstruction module 112, a filter module
113, a decoded picture buffer 114, and an entropy encoding module
116. Prediction module 100 includes a motion estimation module 122,
a motion compensation module 124, and an intra prediction module
126. In other examples, video encoder 20 may include more, fewer,
or different functional components. Furthermore, motion estimation
module 122 and motion compensation module 124 may be highly
integrated, but are represented in the example of FIG. 4 separately
for purposes of explanation.
[0080] Video encoder 20 may receive video data. Video encoder 20
may receive the video data from various sources. For example, video
encoder 20 may receive the video data from video source 18 (FIG. 1)
or another source. The video data may represent a series of
pictures. To encode the video data, video encoder 20 may perform an
encoding operation on each of the pictures. As part of performing
the encoding operation on a picture, video encoder 20 may perform
encoding operations on each slice of the picture. As part of
performing an encoding operation on a slice, video encoder 20 may
perform encoding operations on treeblocks in the slice.
[0081] As part of performing an encoding operation on a treeblock,
prediction module 100 may perform quadtree partitioning on the
video block of the treeblock to divide the video block into
progressively smaller video blocks. Each of the smaller video
blocks may be associated with a different CU. For example,
prediction module 100 may partition a video block of a treeblock
into four equally-sized sub-blocks, partition one or more of the
sub-blocks into four equally-sized sub-sub-blocks, and so on.
[0082] The sizes of the video blocks associated with CUs may range
from 8.times.8 samples up to the size of the treeblock with a
maximum of 64.times.64 samples or greater. In this disclosure,
"N.times.N" and "N by N" may be used interchangeably to refer to
the sample dimensions of a video block in terms of vertical and
horizontal dimensions, e.g., 16.times.16 samples or 16 by 16
samples. In general, a 16.times.16 video block has sixteen samples
in a vertical direction (y=16) and sixteen samples in a horizontal
direction (x=16). Likewise, an N.times.N block generally has N
samples in a vertical direction and N samples in a horizontal
direction, where N represents a nonnegative integer value.
[0083] Furthermore, as part of performing the encoding operation on
a treeblock, prediction module 100 may generate a hierarchical
quadtree data structure for the treeblock. For example, a treeblock
may correspond to a root node of the quadtree data structure. If
prediction module 100 partitions the video block of the treeblock
into four sub-blocks, the root node has four child nodes in the
quadtree data structure. Each of the child nodes corresponds to a
CU associated with one of the sub-blocks. If prediction module 100
partitions one of the sub-blocks into four sub-sub-blocks, the node
corresponding to the CU associated with the sub-block may have four
child nodes, each of which corresponds to a CU associated with one
of the sub-sub-blocks, and so on.
[0084] Each node of the quadtree data structure may contain syntax
data (e.g., syntax elements) for the corresponding treeblock or CU.
For example, a node in the quadtree may include a split flag that
indicates whether the video block of the CU corresponding to the
node is partitioned (i.e., split) into four sub-blocks. Syntax
elements for a CU may be defined recursively, and may depend on
whether the video block of the CU is split into sub-blocks. A CU
whose video block is not partitioned may correspond to a leaf node
in the quadtree data structure. A coded treeblock may include data
based on the quadtree data structure for a corresponding
treeblock.
[0085] Video encoder 20 may perform encoding operations on each
non-partitioned CU of a treeblock. When video encoder 20 performs
an encoding operation on a non-partitioned CU, video encoder 20 may
generate data representing an encoded representation of the
non-partitioned CU.
[0086] As part of performing an encoding operation on a CU,
prediction module 100 may partition the video block of the CU among
one or more PUs of the CU. Video encoder 20 and video decoder 30
may support various PU sizes. Assuming that the size of a
particular CU is 2N.times.2N, video encoder 20 and video decoder 30
may support intra-prediction PU sizes of 2N.times.2N or N.times.N,
and inter-prediction in symmetric PU sizes of 2N.times.2N,
2N.times.N, N.times.2N, N.times.N, or similar. Video encoder 20 and
video decoder 30 may also support asymmetric partitioning for PU
sizes of 2N.times.nU, 2N.times.nD, nL.times.2N, and nR.times.2N. In
some examples, prediction module 100 may perform geometric
partitioning to partition the video block of a CU among PUs of the
CU along a boundary that does not meet the sides of the video block
of the CU at right angles.
[0087] Motion estimation module 122 and motion compensation module
124 may perform inter prediction on each PU of the CU. Inter
prediction may provide temporal compression. By performing inter
prediction on a PU, motion estimation module 122 and motion
compensation module 124 may generate prediction data for the PU
based on decoded samples of reference pictures other than the
picture associated with the CU. The prediction data for the PU may
include a predicted video block and various syntax elements.
[0088] Furthermore, when motion estimation module 122 performs a
motion estimation operation with regard to a PU, motion estimation
module 122 may generate one or more motion vectors for the PU. For
instance, slices may be I slices, P slices, or B slices. Motion
estimation module 122 and motion compensation module 124 may
perform different operations for a PU of a CU depending on whether
the PU is in an I slice, a P slice, or a B slice. In an I slice,
all PUs are intra predicted. Hence, if the PU is in an I slice,
motion estimation module 122 and motion compensation module 124 do
not perform inter prediction on the PU.
[0089] If the PU is in a P slice, the picture containing the PU is
associated with a list of reference pictures referred to as "list
0." Each of the reference pictures in list 0 contains samples that
may be used for inter prediction of subsequent pictures in decoding
order. When motion estimation module 122 performs the motion
estimation operation with regard to a PU in a P slice, motion
estimation module 122 may search the reference pictures in list 0
for a reference sample for the PU. The reference sample of the PU
may be a set of samples, e.g., a block of samples, that most
closely corresponds to the samples in the video block of the PU.
Motion estimation module 122 may use a variety of metrics to
determine how closely a set of samples in a reference picture
corresponds to the samples in the video block of a PU. For example,
motion estimation module 122 may determine how closely a set of
samples in a reference picture corresponds to the samples in the
video block of a PU by sum of absolute difference (SAD), sum of
square difference (SSD), or other difference metrics.
[0090] After identifying a reference sample of a PU in a P slice,
motion estimation module 122 may generate a reference index that
indicates the reference picture in list 0 containing the reference
sample and a motion vector that indicates a spatial displacement
between the PU and the reference sample. In various examples,
motion estimation module 122 may generate motion vectors to varying
degrees of precision. For example, motion estimation module 122 may
generate motion vectors at one-quarter sample precision, one-eighth
sample precision, or other fractional sample precision. In the case
of fractional sample precision, reference sample values may be
interpolated from integer-position sample values in the reference
picture. Motion estimation module 122 may output motion information
for the PU to entropy encoding module 116 and motion compensation
module 124. The motion information for the PU may include the
reference index and the motion vector of the PU. Motion
compensation module 124 may use the motion information of a PU to
identify and retrieve the reference sample of the PU.
[0091] If the PU is in a B slice, the picture containing the PU may
be associated with two lists of reference pictures, referred to as
"list 0" and "list 1." Each of the reference pictures in list 0
contains samples that may be used for inter prediction of
subsequent pictures in decoding order. The reference pictures in
list 1 occur before the picture in decoding order but after the
picture in presentation order. In some examples, a picture
containing a B slice may be associated with a list combination that
is a combination of list 0 and list 1.
[0092] Furthermore, if the PU is in a B slice, motion estimation
module 122 may perform uni-directional prediction or bi-directional
prediction for the PU. When motion estimation module 122 performs
uni-directional prediction for the PU, motion estimation module 122
may search the reference pictures of list 0 or list 1 for a
reference sample for the PU. Motion estimation module 122 may then
generate a reference index that indicates the reference picture in
list 0 or list 1 that contains the reference sample and a motion
vector that indicates a spatial displacement between the PU and the
reference sample. Motion estimation module 122 may output syntax
elements that indicate the motion information for the PU to entropy
encoding module 116 and motion compensation module 124. The motion
information for the PU may include the reference index, a
prediction direction indicator, and the motion vector of the PU.
The prediction direction indicator may indicate whether the
reference index indicates a reference picture in list 0 or list 1.
Motion compensation module 124 may use the motion information of
the PU to identify and retrieve the reference sample of the PU.
[0093] When motion estimation module 122 performs bi-directional
prediction for a PU, motion estimation module 122 may search the
reference pictures in list 0 for a reference sample for the PU and
may also search the reference pictures in list 1 for another
reference sample for the PU. Motion estimation module 122 may then
generate reference indexes that indicate the reference pictures in
list 0 and list 1 containing the reference samples and motion
vectors that indicate spatial displacements between the reference
samples and the PU. Motion estimation module 122 may output syntax
elements that indicate the motion information of the PU to entropy
encoding module 116 and motion compensation module 124. The motion
information for the PU may include the reference indexes and the
motion vectors of the PU. Motion compensation module 124 may use
the motion information to identify and retrieve the reference
sample of the PU.
[0094] In some instances, motion estimation module 122 does not
output a full set of motion information for a PU to entropy
encoding module 116. Rather, motion estimation module 122 may
signal the motion information of a PU with reference to the motion
information of another PU. For example, motion estimation module
122 may determine that the motion information of the PU is
sufficiently similar to the motion information of a neighboring PU.
In this example, motion estimation module 122 may indicate, in a
quadtree node for a CU associated with the PU, a value that
indicates to video decoder 30 that the PU has the same motion
information as the neighboring PU. In another example, motion
estimation module 122 may identify, in a quadtree node associated
with the CU associated with the PU, a neighboring PU and a motion
vector difference (MVD). The motion vector difference indicates a
difference between the motion vector of the PU and the motion
vector of the indicated neighboring PU. Video decoder 30 may use
the motion vector of the indicated neighboring PU and the motion
vector difference to predict the motion vector of the PU. By
referring to the motion information of a first PU when signaling
the motion information of a second PU, video encoder 20 may be able
to signal the motion information of the second PU using fewer
bits.
[0095] As part of performing an encoding operation on a CU, intra
prediction module 126 may perform intra prediction on PUs of the
CU. Intra prediction may provide spatial compression. When intra
prediction module 126 performs intra prediction on a PU, intra
prediction module 126 may generate prediction data for the PU based
on decoded samples of other PUs in the same picture. The prediction
data for the PU may include a predicted video block and various
syntax elements. Intra prediction module 126 may perform intra
prediction on PUs in I slices, P slices, and B slices.
[0096] To perform intra prediction on a PU, intra prediction module
126 may use multiple intra prediction modes to generate multiple
sets of prediction data for the PU. When intra prediction module
126 uses an intra prediction mode to generate a set of prediction
data for the PU, intra prediction module 126 may extend samples
from video blocks of neighboring PUs across the video block of the
PU in a direction associated with the intra prediction mode. The
neighboring PUs may be above, above and to the right, above and to
the left, to the left, or below and to the left of the PU. Intra
prediction module 126 may use various numbers of intra prediction
modes, e.g., 35 directional intra prediction modes. Intra
prediction module 126 may perform various intra-prediction
operations. For example, intra prediction module 126 may perform
the example intra-prediction operation of FIG. 6.
[0097] Prediction module 100 may select the prediction data for a
PU from among the prediction data generated by motion compensation
module 124 for the PU or the prediction data generated by intra
prediction module 126 for the PU. In some examples, prediction
module 100 selects the prediction data for the PU based on
rate/distortion metrics of the sets of prediction data.
[0098] If prediction module 100 selects prediction data generated
by intra prediction module 126, prediction module 100 may signal
the intra prediction mode that was used to generate the prediction
data for the PUs, i.e., the selected intra prediction mode.
Prediction module 100 may signal the selected intra prediction mode
in various ways. For example, it is probable the selected intra
prediction mode is the same as the intra prediction mode of a
neighboring PU. In other words, the intra prediction mode of the
neighboring PU may be the most probable mode for the current PU.
Thus, prediction module 100 may generate a syntax element to
indicate that the selected intra prediction mode is the same as the
intra prediction mode of the neighboring PU.
[0099] After prediction module 100 selects the prediction data for
PUs of a CU, residual generation module 102 may generate residual
data for the CU by subtracting the predicted video blocks of the
prediction data of the PUs of the CU from the video block of the
CU. The residual data of a CU may include 2D residual video blocks
that correspond to different sample components of the samples in
the video block of the CU. For example, the residual data may
include a residual video block that corresponds to differences
between luminance components of samples in the predicted video
blocks of the PUs of the CU and luminance components of samples in
the original video block of the CU. In addition, the residual data
of the CU may include residual video blocks that correspond to the
differences between chrominance components of samples in the
predicted video blocks of the PUs of the CU and the chrominance
components of the samples in the original video block of the
CU.
[0100] Prediction module 100 may perform quadtree partitioning to
partition the residual video blocks of a CU into sub-blocks. Each
undivided residual video block may be associated with a different
TU of the CU. The sizes and positions of the residual video blocks
associated with TUs of a CU may or may not be based on the sizes
and positions of video blocks associated with the PUs of the CU. A
quadtree structure known as a "residual quad tree" (RQT) may
include nodes associated with each of the residual video blocks.
The TUs of a CU may correspond to leaf nodes of the RQT.
[0101] Transform module 104 may generate one or more transform
coefficient blocks for each TU of a CU by applying one or more
transforms to a residual video block associated with the TU. Each
of the transform coefficient blocks may be a 2D matrix of transform
coefficients. Transform module 104 may apply various transforms to
the residual video block associated with a TU. For example,
transform module 104 may apply a discrete cosine transform (DCT), a
directional transform, or a conceptually similar transform to the
residual video block associated with a TU.
[0102] After transform module 104 generates a transform coefficient
block associated with a TU, quantization module 106 may quantize
the transform coefficients in the transform coefficient block.
Quantization module 106 may quantize a transform coefficient block
associated with a TU of a CU based on a QP value associated with
the CU.
[0103] Video encoder 20 may associate a QP value with a CU in
various ways. For example, video encoder 20 may perform a
rate-distortion analysis on a treeblock associated with the CU. In
the rate-distortion analysis, video encoder 20 may generate
multiple coded representations of the treeblock by performing an
encoding operation multiple times on the treeblock. Video encoder
20 may associate different QP values with the CU when video encoder
20 generates different encoded representations of the treeblock.
Video encoder 20 may signal that a given QP value is associated
with the CU when the given QP value is associated with the CU in a
coded representation of the treeblock that has a lowest bitrate and
distortion metric.
[0104] Inverse quantization module 108 and inverse transform module
110 may apply inverse quantization and inverse transforms to the
transform coefficient block, respectively, to reconstruct a
residual video block from the transform coefficient block.
Reconstruction module 112 may add the reconstructed residual video
block to corresponding samples from one or more predicted video
blocks generated by prediction module 100 to produce a
reconstructed video block associated with a TU. By reconstructing
video blocks for each TU of a CU in this way, video encoder 20 may
reconstruct the video block of the CU.
[0105] After reconstruction module 112 reconstructs the video block
of a CU, filter module 113 may perform a deblocking operation to
reduce blocking artifacts in the video block associated with the
CU. After performing the deblocking operations, filter module 113
may store the reconstructed video block of the CU in decoded
picture buffer 114. Motion estimation module 122 and motion
compensation module 124 may use a reference picture that contains
the reconstructed video block to perform inter prediction on PUs of
subsequent pictures. In addition, intra prediction module 126 may
use reconstructed video blocks in decoded picture buffer 114 to
perform intra prediction on other PUs in the same picture as the
CU.
[0106] Entropy encoding module 116 may receive data from other
functional components of video encoder 20. For example, entropy
encoding module 116 may receive transform coefficient blocks from
quantization module 106 and may receive syntax elements from
prediction module 100. When entropy encoding module 116 receives
the data, entropy encoding module 116 may perform one or more
entropy encoding operations to generate entropy encoded data. For
example, video encoder 20 may perform a context adaptive variable
length coding (CAVLC) operation, a context-adaptive binary
arithmetic coding (CABAC) operation, a variable-to-variable (V2V)
length coding operation, a syntax-based context-adaptive binary
arithmetic coding (SBAC) operation, a Probability Interval
Partitioning Entropy (PIPE) coding operation, or another type of
entropy encoding operation on the data. Entropy encoding module 116
may output a bitstream that includes the entropy encoded data.
[0107] As part of performing an entropy encoding operation on data,
entropy encoding module 116 may select a context model. If entropy
encoding module 116 is performing a CABAC operation, the context
model may indicate probabilities of a bin having particular values.
In the context of CABAC, the term "bin" is used to refer to a bit
of a binarized version of a syntax element.
[0108] If the entropy encoding module 116 is performing a CAVLC
operation, the context model may map coefficients to corresponding
codewords. Codewords in CAVLC may be constructed such that
relatively short codes correspond to more probable symbols, while
relatively long codes correspond to less probable symbols.
Selection of an appropriate context model may impact coding
efficiency of the entropy encoding operation.
[0109] In some example, video encoder 20 may divide the CUs of a
slice into a plurality of tiles. Video encoder 20 may divide the
CUs into tiles by defining two or more horizontal boundaries for a
picture and two or more vertical boundaries for the picture. The
horizontal boundaries may include the top and bottom edges of the
picture. The vertical boundaries may include the left and right
sides of the picture. When the video encoder does not use tiles,
video encoder 20 may encode all of the treeblocks of the frame in
raster scan order. However, when video encoder 20 uses tiles, the
video encoder may encode the tiles in raster scan order. When video
encoder 20 encodes a tile, video encoder 20 may encode the
treeblocks (i.e., LCUs) within the tile in raster scan order. Thus,
video encoder 20 may use tiles to change the encoding order of the
treeblocks of the picture.
[0110] Furthermore, in some instances, when video encoder 20 is
encoding a given CU, video encoder 20 may use information
associated with spatially-neighboring CUs to perform intra
prediction on the given CU, so long as the given CU and the
spatially-neighboring CUs belong to the same tile. The
spatially-neighboring CUs may be CUs that are in the same picture
as the given CU. (When video encoder 20 performs inter prediction
on the given CU, video encoder 20 may also use motion and pixel
information from temporally-neighboring CUs, regardless of the
tiles of the temporally-neighboring CUs.) Similarly, in some
instances, when video encoder 20 is encoding a given CU, video
encoder 20 may use information associated with
spatially-neighboring CUs to select a context for entropy encoding
a syntax element of the given CU, so long as the given CU and the
spatially-neighboring CUs are in the same tile. Because of these
restrictions, video encoder 20 may be able to encode two or more of
the tiles in parallel.
[0111] FIG. 5 is a block diagram that illustrates an example video
decoder 30 that may implement the techniques of this disclosure.
FIG. 5 is provided for purposes of explanation and is not limiting
on the techniques as broadly exemplified and described in this
disclosure. For purposes of explanation, this disclosure describes
video decoder 30 in the context of HEVC coding. However, the
techniques of this disclosure may be applicable to other coding
standards or methods.
[0112] In the example of FIG. 5, video decoder 30 includes a
plurality of functional components. The functional components of
video decoder 30 include an entropy decoding module 150, a
prediction module 152, an inverse quantization module 154, an
inverse transform module 156, a reconstruction module 158, a filter
module 159, and a decoded picture buffer 160. Prediction module 152
includes a motion compensation module 162 and an intra prediction
module 164. In some examples, video decoder 30 may perform a
decoding pass generally reciprocal to the encoding pass described
with respect to video encoder 20 of FIG. 4. In other examples,
video decoder 30 may include more, fewer, or different functional
components.
[0113] Video decoder 30 may receive a bitstream that comprises
encoded video data. The bitstream may include a plurality of syntax
elements. When video decoder 30 receives the bitstream, entropy
decoding module 150 may perform a parsing operation on the
bitstream. As a result of performing the parsing operation on the
bitstream, entropy decoding module 150 may extract syntax elements
from the bitstream. As part of performing the parsing operation,
entropy decoding module 150 may entropy decode entropy encoded
syntax elements in the bitstream. Prediction module 152, inverse
quantization module 154, inverse transform module 156,
reconstruction module 158, and filter module 159 may perform a
reconstruction operation that generates decoded video data based on
the syntax elements extracted from the bitstream.
[0114] As discussed above, the bitstream may comprise a series of
NAL units. The NAL units of the bitstream may include sequence
parameter set NAL units, picture parameter set NAL units, SEI NAL
units, and so on. As part of performing the parsing operation on
the bitstream, entropy decoding module 150 may perform parsing
operations that extract and entropy decode sequence parameter sets
from sequence parameter set NAL units, picture parameter sets from
picture parameter set NAL units, SEI data from SEI NAL units, and
so on.
[0115] In addition, the NAL units of the bitstream may include
coded slice NAL units. As part of performing the parsing operation
on the bitstream, entropy decoding module 150 may perform parsing
operations that extract and entropy decode coded slices from the
coded slice NAL units. Each of the coded slices may include a slice
header and slice data. The slice header may contain syntax elements
pertaining to a slice. The syntax elements in the slice header may
include a syntax element that identifies a picture parameter set
associated with a picture that contains the slice. Entropy decoding
module 150 may perform an entropy decoding operation, such as a
CAVLC decoding operation, on the coded slice header to recover the
slice header.
[0116] After extracting the slice data from coded slice NAL units,
entropy decoding module 150 may extract coded treeblocks from the
slice data. Entropy decoding module 150 may then extract coded CUs
from the coded treeblocks. Entropy decoding module 150 may perform
parsing operations that extract syntax elements from the coded CUs.
The extracted syntax elements may include entropy-encoded transform
coefficient blocks. Entropy decoding module 150 may then perform
entropy decoding operations on the syntax elements. For instance,
entropy decoding module 150 may perform CABAC operations on the
transform coefficient blocks.
[0117] After entropy decoding module 150 performs a parsing
operation on a non-partitioned CU, video decoder 30 may perform a
reconstruction operation on the non-partitioned CU. To perform the
reconstruction operation on a non-partitioned CU, video decoder 30
may perform a reconstruction operation on each TU of the CU. By
performing the reconstruction operation for each TU of the CU,
video decoder 30 may reconstruct a residual video block associated
with the CU.
[0118] As part of performing a reconstruction operation on a TU,
inverse quantization module 154 may inverse quantize, i.e.,
de-quantize, a transform coefficient block associated with the TU.
Inverse quantization module 154 may inverse quantize the transform
coefficient block in a manner similar to the inverse quantization
processes proposed for HEVC or defined by the H.264 decoding
standard. Inverse quantization module 154 may use a quantization
parameter QP calculated by video encoder 20 for a CU of the
transform coefficient block to determine a degree of quantization
and, likewise, a degree of inverse quantization for inverse
quantization module 154 to apply.
[0119] After inverse quantization module 154 inverse quantizes a
transform coefficient block, inverse transform module 156 may
generate a residual video block for the TU associated with the
transform coefficient block. Inverse transform module 156 may apply
an inverse transform to the transform coefficient block in order to
generate the residual video block for the TU. For example, inverse
transform module 156 may apply an inverse DCT, an inverse integer
transform, an inverse Karhunen-Loeve transform (KLT), an inverse
rotational transform, an inverse directional transform, or another
inverse transform to the transform coefficient block.
[0120] In some examples, inverse transform module 156 may determine
an inverse transform to apply to the transform coefficient block
based on signaling from video encoder 20. In such examples, inverse
transform module 156 may determine the inverse transform based on a
signaled transform at the root node of a quadtree for a treeblock
associated with the transform coefficient block. In other examples,
inverse transform module 156 may infer the inverse transform from
one or more coding characteristics, such as block size, coding
mode, or the like. In some examples, inverse transform module 156
may apply a cascaded inverse transform.
[0121] If a PU of the CU was encoded using inter prediction, motion
compensation module 162 may perform motion compensation to generate
a predicted video block for the PU. Motion compensation module 162
may use motion information for the PU to identify a reference
sample for the PU. The reference sample of a PU may be in a
different temporal picture than the PU. The motion information for
the PU may include a motion vector, a reference picture index, and
a prediction direction. Motion compensation module 162 may use the
reference sample for the PU to generate the predicted video block
for the PU. In some examples, motion compensation module 162 may
predict the motion information for the PU based on motion
information of PUs that neighbor the PU. In this disclosure, a PU
is an inter-predicted PU if video encoder 20 uses inter prediction
to generate the predicted video block of the PU.
[0122] In some examples, motion compensation module 162 may refine
the predicted video block of a PU by performing interpolation based
on interpolation filters. Identifiers for interpolation filters to
be used for motion compensation with sub-sample precision may be
included in the syntax elements. Motion compensation module 162 may
use the same interpolation filters used by video encoder 20 during
generation of the predicted video block of the PU to calculate
interpolated values for sub-integer samples of a reference block.
Motion compensation module 162 may determine the interpolation
filters used by video encoder 20 according to received syntax
information and use the interpolation filters to produce the
predicted video block.
[0123] If a PU is encoded using intra prediction, intra prediction
module 164 may perform intra prediction to generate a predicted
video block for the PU. For example, intra prediction module 164
may determine an intra prediction mode for the PU based on syntax
elements in the bitstream. The bitstream may include syntax
elements that intra prediction module 164 may use to predict the
intra prediction mode of the PU. For example, intra prediction
module 164 may perform the example intra-prediction operation of
FIG. 6.
[0124] In some instances, the syntax elements may indicate that
intra prediction module 164 is to use the intra prediction mode of
another PU to predict the intra prediction mode of the current PU.
For example, it may be probable that the intra prediction mode of
the current PU is the same as the intra prediction mode of a
neighboring PU. In other words, the intra prediction mode of the
neighboring PU may be the most probable mode for the current PU.
Hence, in this example, the bitstream may include a small syntax
element that indicates that the intra prediction mode of the PU is
the same as the intra prediction mode of the neighboring PU. Intra
prediction module 164 may then use the intra prediction mode to
generate prediction data (e.g., predicted samples) for the PU based
on the video blocks of spatially neighboring PUs.
[0125] Reconstruction module 158 may use the residual video blocks
associated with TUs of a CU and the predicted video blocks of the
PUs of the CU, i.e., either intra-prediction data or
inter-prediction data, as applicable, to reconstruct the video
block of the CU. Thus, video decoder 30 may generate a predicted
video block and a residual video block based on syntax elements in
the bitstream and may generate a video block based on the predicted
video block and the residual video block. After reconstruction
module 158 reconstructs the video block of the CU, filter module
159 may perform filter module 159 may perform a deblocking
operation to reduce blocking artifacts associated with the CU.
[0126] Decoded picture buffer 160 may store decoded samples for
pictures of the video data. Thus, after filter module 159 performs
the deblocking operation, video decoder 30 may store the video
block of the CU in decoded picture buffer 160. Decoded picture
buffer 160 may provide reference pictures for subsequent motion
compensation, intra prediction, and presentation on a display
device, such as display device 32 of FIG. 1. For instance, video
decoder 30 may perform, based on the video blocks in decoded
picture buffer 160, intra prediction or inter prediction operations
on PUs of other CUs.
[0127] FIG. 6 is a flowchart that illustrates an example
intra-prediction operation 200. A video coder, such as video
encoder 20 or video decoder 30, may perform intra-prediction
operation 200. In other examples, the video coder may use
intra-prediction operations other than intra-prediction operation
200. For instance, in other examples, the video coder may perform
an intra-prediction operation in which the video coder performs
more, fewer, or different steps than intra-prediction operation
200.
[0128] After the video coder starts intra-prediction operation 200,
the video coder may perform a padding operation for a PU (202).
When the video coder performs the padding operation, the video
coder may assign values to unavailable border pixels associated
with the PU. The video coder may perform various padding
operations. For instance, the video coder may perform the example
padding operation of FIG. 7, the example padding operation of FIG.
8, the example padding operation of FIG. 10, or another padding
operation.
[0129] After the video coder performs the padding operation, the
video coder may generate, based on the border pixels, an
intra-predicted video block for the PU (204). The video coder may
use some or all of the border pixels to generate the
intra-predicted video block.
[0130] FIG. 7 is a flowchart that illustrates an example padding
operation 250. A video coder, such as video encoder 20 or video
decoder 30, may perform padding operation 250. In other examples,
the video coder may use padding operations other than padding
operation 250. For instance, in other examples, the video coder may
perform a padding operation in which the video coder performs more,
fewer, or different steps than padding operation 250.
[0131] After the video coder starts padding operation 250, the
video coder may set a pixel indicator to indicate a bottom-left
border pixel (252). For instance, in the example of FIG. 2, the
video coder may set the pixel indicator to indicate border pixel P.
For ease of explanation, this disclosure may refer to the border
pixel indicated by the pixel indicator as the current border
pixel.
[0132] Next, the video coder may determine whether the current
border pixel is available (254). The video coder may determine
whether the current border pixel is available in various ways. For
example, the video coder may perform the example operation of FIG.
13 to determine whether the current border pixel is available.
[0133] In response to determining that the current border pixel is
not available ("NO" of 254), the video coder may assign a default
value to the current border pixel (256). Because the current border
pixel is the bottom-left border pixel, the video coder may
determine whether the bottom-left border pixel is available and
assign a default value to the bottom-left border pixel in response
to determining that the bottom-left border pixel is not available.
In another example, the video coder may assign a value of a next
available border pixel to the bottom-left border pixel in response
to determining that the bottom-left border pixel is
unavailable.
[0134] After assigning a value to the current border pixel or in
response to determining that the current border pixel is available
("YES" of 254), the video coder may update the pixel indicator to
indicate a next border pixel (258). If the current border pixel is
between the bottom-left border pixel and the corner border pixel
(e.g., border pixel R in FIG. 2), the next border pixel is
immediately above the current border pixel. For instance, in the
example of FIG. 2, if the current border pixel is border pixel P,
the next border pixel is border pixel O. If the current border
pixel is border pixel O, the next border pixel is border pixel N,
and so on. If the current pixel is the corner border pixel or
between the corner border pixel and the top-right border pixel
(e.g., border pixel H in FIG. 2), the next border pixel is
immediately to the right of the current border pixel. For instance,
in the example of FIG. 2, if the current border pixel is border
pixel R, the next border pixel is border pixel A. If the current
border pixel is border pixel A, the next border pixel is border
pixel B, and so on. By updating the pixel indicator, the next
border pixel becomes the current border pixel.
[0135] After updating the pixel indicator, the video coder may
determine whether the current border pixel is available (260). In
response to determining that the current border pixel is not
available ("NO" of 260), the video coder may assign the value of
the previous border pixel to the current border pixel (262). In
other words, the video coder may assign to the current border pixel
a value of a border pixel that is immediately before the current
border pixel according to the order. For instance, in the example
of FIG. 2, if the current border pixel is border pixel M and border
pixel M is unavailable, the video coder may assign the value of
border pixel N to border pixel M. If the current border pixel is
border pixel L and border pixel L is unavailable, the video coder
may assign the value of border pixel M to border pixel L, and so
on. When the video coder assigns a value of a first border pixel to
a second border pixel, the video coder may not change the actual
value of the second border pixel, but may use the value of the
first border pixel as the value of the second border pixel for
purposes of generating an intra-predicted video block.
[0136] After performing step 262 or in response to determining that
the current border pixel is available ("YES" of 260), the video
coder may determine whether the current border pixel is the
top-right border pixel (264). For instance, in the example of FIG.
2, the video coder may determine whether the current border pixel
is border pixel H. The video coder may end padding operation 250 in
response to determining that the current border pixel is the
top-right border pixel ("YES" of 264). On the other hand, in
response to determining that the current border pixel is not the
top-right border pixel ("NO" of 264), the video coder may again
update the pixel indicator (258). The video coder may then repeat
steps 260-264 with regard to the new current border pixel.
[0137] In this way, the video coder may perform a padding operation
that processes a set of border pixels according to an order that
starts at a bottom-left border pixel and proceeds through the
border pixels sequentially to a top-right border pixel. When the
padding operation processes an unavailable border pixel, the
padding operation assigns a value to the unavailable border pixel
based on a value of a pixel previously processed by the padding
operation.
[0138] In an example padding operation similar to padding operation
250, (x, y) indicates the coordinates of the video block and
(x-1,y-1) indicates the coordinates of the corner border pixel. If
(x-1, y-1) is unavailable, the video coder may check the top
predictor from left to right until the video coder reaches an
available border pixel. If the available border pixel has
coordinates (x+d, y-1), the video coder may assign the value of the
border pixel at (x+d, y-1) to all border pixels from (x-1, y-1) to
(x+d-1, y-1). Otherwise, if the border pixel at (x-1, y-1) is
available, the video coder may set a variable d to -1 and execute
the following pseudo-code:
TABLE-US-00001 for (i = d; i<2N; i++) { if the border pixel at
(x+i, y-1) is available, do nothing if the border pixel at (x+i,
y-1) is unavailable, assign the value of the border pixel at
(x+i-1, y-1) to the border pixel at (x+i, y-1) }
In the pseudo-code above, N may indicate the width of the video
block. In addition, the video coder may determine whether the
border pixel at (x-1, y) is available. If the border pixel at (x-1,
y) is not available, the video coder may check the left predictor
from top to bottom until the video coder reaches an available
border pixel. If the available border pixel has coordinates (x-1,
y+d), the video coder may assign the value of the border pixel at
(x-1, y+d) to all border pixels from (x-1, y) to (x-1, y+d-1).
Otherwise, if the border pixel at (x-1, y) is available, the video
coder may set a variable d to 0 and execute the following
pseudo-code:
TABLE-US-00002 for (i = d; i<2N; i++) { if the border pixel at
(x-1, y+i) is available, do nothing if the border pixel at (x-1,
y+i) is unavailable, assign the value of the border pixel at (x-1,
y+i-1) to the border pixel at (x-1, y+i) }
[0139] In the example of FIG. 7, for x=-1, y=nS*2-2 . . . -1, the
video coder may substitute a value of p[x, y+1] for a value of p[x,
y] if p[x, y] is an unavailable border pixel. For x=0..nS*2-1, y-1,
substituting a value of p[x-1, y] for a value of p[x, y] if p[x, y]
is an unavailable border pixel. nS is equal to a width or height of
the intra-predicted video block, p is a two-dimensional array of
samples, and p[0,0] is a top-left luma sample of the
intra-predicted video block.
[0140] FIG. 8 is a conceptual diagram that illustrates an order in
which the example padding operation of FIG. 7 proceeds through
border pixels. As illustrated in the example of FIG. 8, the padding
operation starts at the bottom-left border pixel, proceeds upward
to the corner border pixel, and then proceeds rightward to the
upper-right border pixel.
[0141] FIG. 9 is a flowchart that illustrates an example padding
operation 300. A video coder, such as video encoder 20 or video
decoder 30, may perform padding operation 300. In other examples,
the video coder may use padding operations other than padding
operation 300. For instance, in other examples, the video coder may
perform a padding operation in which the video coder performs more,
fewer, or different steps than padding operation 300.
[0142] After the video coder starts padding operation 300, the
video coder may set a first pixel indicator and a second pixel
indicator to indicate a division point (302). The division point
may divide the border pixels into two segments. One of the segments
may include border pixels that are above and to the right of the
division point. The other one of the segments may include border
pixels that are below and to the left of the division point.
[0143] The division point may be various ones of the border pixels.
For example, the video coder may set the first and the second pixel
indicators to the corner border pixel (e.g., border pixel R in FIG.
2). In another example, the video coder may set the first pixel
indicator and the second pixel indicator to indicate another border
pixel (e.g., border pixel L in FIG. 2).
[0144] After setting the first and second pixel indicators to
indicate the division point, the video coder may determine whether
the division point is available (304). The video coder may
determine whether the division point is available in various ways.
For example, the video coder may perform the example operation of
FIG. 13 to determine whether the division point is available.
[0145] In response to determining that the division point is not
available ("NO" of 304), the video coder may derive a value of the
division point (306). The video coder may derive the value of the
division point in various ways. For example, the video coder may
determine whether either of the border pixels adjacent to the
division point is available. In this example, if one of the border
pixels adjacent to the division point is available, the video coder
may derive the value of the division point by assigning the value
of the adjacent border pixel to the division point. Furthermore, in
this example, the video coder may assign a default value to the
division point if neither of the adjacent border pixels is
available. For instance, if the division point is the corner
division point, the video coder may use the following pseudo-code
to derive a value of the division point:
TABLE-US-00003 If P.sub.L1 is available, P.sub.pad = P.sub.L1,
otherwise, if P.sub.A1 is available, P.sub.pad = P.sub.A1,
otherwise, P.sub.pad = a default value.
In the pseudo-code above, P.sub.L1 may indicate the value of the
border pixel below the corner border pixel, P.sub.pad may indicate
the derived value to be assigned to the corner border pixel, and
P.sub.A1 may indicate the value of the border pixel to the right of
the corner border pixel. In the case that the corner border pixel
and both the border pixel below and the border pixel to the right
of the corner border pixel are unavailable, using a default value
for the corner border pixel may have little impact on coding
performance since this case may happen rarely.
[0146] After deriving the value of the division point or after
determining that the division point is available ("YES" of 304),
the video coder may update the first pixel indicator to indicate a
border pixel that is below or to the left of the border pixel
indicated by the first pixel indicator (308). For ease of
explanation, this disclosure may refer to the border pixel
indicated by the first pixel indicator as the first current border
pixel. For instance, in the example of FIG. 2, if the first current
border pixel is border pixel B, the video coder may update the
first pixel indicator to indicate the border pixel A. If the first
current border pixel is border pixel R, the video coder may update
the first pixel indicator to indicate border pixel I. If the first
current border pixel is border pixel I, the video coder may update
the first pixel indicator to indicate border pixel J.
[0147] After updating the first pixel indicator, the video coder
may determine whether the first current border pixel is available
(310). The video coder may determine whether the first current
border pixel is available in various ways. For example, the video
coder may perform the example operation of FIG. 13 to determine
whether the first current border pixel is available.
[0148] In response to determining that the first current border
pixel is unavailable ("NO" of 310), the video coder may assign the
value of the previous border pixel to the first current border
pixel (312). For instance, in the example of FIG. 2, if the first
current border pixel is border pixel I and border pixel I is
unavailable, the video coder may assign the value of the border
pixel R to border pixel I. If the first current border pixel is
border pixel J and border pixel J is unavailable, the video coder
may assign the value of the border pixel I to border pixel J, and
so on.
[0149] Once the video coder has performed step 310 or after
determining that the first current border pixel is available ("YES"
of 310), the video coder may determine whether the first current
border pixel is the bottom-left border pixel (314). In response to
determining that the first current border pixel is the bottom-left
border pixel ("YES" of 314), the video coder may end padding
operation 300 with regard to border pixels occurring left of or
below of the division point border pixel. However, in response to
determining that the first current border pixel is not the
bottom-left border pixel ("NO" of 314), the video coder may again
update the first pixel indicator (308) and perform steps 310-314
with regard to another border pixel. In this way, padding operation
300 may assign values to each unavailable border pixel left of or
below the division point border pixel.
[0150] In addition, after deriving the value of the division point
border pixel in step 306 or in response to determining that the
division point is available ("YES" of 304), the video coder may
update the second pixel indicator to indicate a border pixel that
is above or to the right of the border pixel indicated by the
second pixel indicator (316). For ease of explanation, this
disclosure may refer to the border pixel indicated by the second
pixel indicator as the second current border pixel.
[0151] After updating the second pixel indicator, the video coder
may determine whether the second current border pixel is available
(318). The video coder may determine whether the current border
pixel is available in various ways. For example, the video coder
may perform the example operation of FIG. 13 to determine whether
the second current border pixel is available.
[0152] In response to determining that the second current border
pixel is unavailable ("NO" of 318), the video coder may assign the
value of a previous border pixel to the second current border pixel
(320). For instance, in the example of FIG. 2, if the second
current border pixel is border pixel D and border pixel D is
unavailable, the video coder may assign the value of border pixel C
to border pixel D.
[0153] After performing step 320 or after the video coder has
determined that the second current border pixel is available ("YES"
of 318), the video coder may determine whether the second current
border pixel is the top-right border pixel (322). In response to
determining that the second current border pixel is the top-right
border pixel, the video coder may end padding operation 300 with
regard to border pixels that are to the right or above the division
point border pixel ("YES" of 322). However, in response to
determining that the second current border pixel is not the
top-right border pixel ("NO" of 322), the video coder may update
the second pixel indicator (316) and perform steps 318-322 with
regard to another border pixel. In this way, the video coder may
process each border pixel that is above or to the right of the
division point.
[0154] In the example of FIG. 9, the video coder may perform steps
308-314 and steps 316-322 in parallel. In other examples, the video
coder may perform steps 308-314 and steps 316-322 sequentially.
[0155] FIG. 10 is a conceptual diagram that illustrates an example
order in which the padding operation of FIG. 9 proceeds through
border pixels. As illustrated in the example of FIG. 10, the corner
border pixel is the division point border pixel. The video coder
may concurrently process border pixels below the corner border
pixel (e.g., in steps 308-314) and border pixels right of the
corner border pixel (e.g., steps 316-322). In the example of FIG.
10, the corner border pixel is shaded. If the corner border pixel
is unavailable, the video coder may derive a value for the corner
border pixel from either or both of neighboring border pixels
340.
[0156] In another example, the video coder may check from left to
right across the top predictor until the video coder identifies an
available border pixel. The video coder may then set the corner
pixel and all border pixels between the corner pixel and the
available border pixel to the value of the available border pixel.
In this example, if the border pixel below the corner pixel is
unavailable, the video coder may check from top to bottom along the
left predictor until the video coder identifies an available border
pixel. The video coder may then set each border pixel below the
corner pixel to the value of the available border pixel.
[0157] FIG. 11 is a flowchart that illustrates an example padding
operation 350. A video coder, such as video encoder 20 or video
decoder 30, may perform padding operation 350. In other examples,
the video coder may use padding operations other than padding
operation 350. For instance, in other examples, the video coder may
perform a padding operation in which the video coder performs more,
fewer, or different steps than padding operation 350.
[0158] In padding operation 350, the border pixels include a
plurality of candidate division points. The plurality of candidate
division points may include various ones of the border pixels. For
example, the plurality of candidate division points may include the
corner border pixel, a border pixel midway between the corner
border pixel and the bottom-left border pixel, and a border pixel
midway between the corner border pixel and the upper-right border
pixel. In another example, the plurality of candidate division
points may include the bottom-left border pixel and the upper-right
border pixel. In another example, the plurality of candidate
division points may include the border pixel immediately to the
right of the corner border pixel and the border pixel immediately
below the corner border pixel.
[0159] In another example, the plurality of candidate division
points may include all border pixels between two border pixels,
P.sub.LX and P.sub.AY. In this example, P.sub.LX may be any border
pixel from the corner border pixel to a bottom-left border pixel
and P.sub.AY may be any border pixel from the corner border pixel
to the top-right border pixel. In this example, the video coder may
search through the candidate division points sequentially from
P.sub.LX to P.sub.AY or from P.sub.AY to P.sub.LX for an available
candidate division point. Searching for an available candidate
division point in this manner may reduce searching complexity to a
one dimensional search. For instance, in this example, if the
division point is the bottom-left border pixel, the video coder to
perform a padding operation that processes the set of border pixels
according to an order that starts at the bottom-left border pixel
and proceeds through the border pixels sequentially to a top-right
border pixel, wherein when the padding operation processes an
unavailable border pixel, the padding operation assigns a value to
the unavailable border pixel based on a value of a border pixel
previously processed by the padding operation.
[0160] In another example, the plurality of candidate division
points may include all of the border pixels. In this example, the
video coder may search for an available candidate division point
through the candidate division points sequentially from a
bottom-left border pixel to a top-right border pixel or vice versa.
Searching for an available candidate division point in this manner
may reduce searching complexity to a one directional search.
[0161] After the video coder starts padding operation 350, the
video coder may set a division point indicator to indicate a first
one of the candidate division points (352). For ease of
explanation, this disclosure may refer to the candidate division
point indicated by the division point indicator as the current
division point. For instance, if the plurality of candidate
division points includes the corner border pixel, the video coder
may set the division point indicator to the corner border
pixel.
[0162] After setting the division point indicator to indicate one
of the candidate division points, the video coder may determine
whether the current division point is available (354). The video
coder may determine whether the current division point is available
in various ways. For example, the video coder may perform the
example operation of FIG. 13 to determine whether the current
division point is available.
[0163] If the current division point is unavailable ("NO" of 354),
the video coder may determine whether the current division point is
a last one of the candidate division points to be checked (356). In
response to determining that the current division point is the last
one of the candidate division points, the video coder may assign a
default value to the current division point (358). In other
examples, the video coder may assign a value based on the values of
neighboring pixels to the current division point instead of using
the default value.
[0164] On the other hand, in response to determining that the
current division point is not the last one of the candidate
division points, the video coder may update the division point
indicator such that the division point indicator indicates a next
one of the candidate division points (360). For instance, in the
example of FIG. 2, the plurality of candidate division points may
include border pixel L, border pixel R, and border pixel D. If the
current division point is border pixel L and border pixel L is
unavailable, the video coder may update the division point
indicator such that the division point indicator indicates border
pixel R. The video coder may search for an available candidate
division point in various ways. For example, the video coder may
start with a candidate division point that is closest to the
bottom-left border pixel and then search through the candidate
division points toward the candidate division point that is closest
to the top-right border pixel.
[0165] After updating the division point indicator, the video coder
may determine again whether the current division point is available
(354). In this way, the video coder may process candidate division
points until the video coder determines that one of the candidate
division points is available or until the video coder determines
that none of the candidate division points is available, or vice
versa.
[0166] After performing step 358 or after determining that the
current division point is available ("YES" of 354), the video coder
may set a first pixel indicator and a second pixel indicator to
indicate the current division point (362). For example, if the
current division point is the corner border pixel, the video coder
may set the first and the second pixel indicators to indicate the
corner border pixel (e.g., border pixel R in FIG. 2).
[0167] After setting the first and second pixel indicators to
indicate the current division point, the video coder may update the
first pixel indicator to indicate a border pixel that is below or
to the left of the border pixel indicated by the first pixel
indicator (364). For ease of explanation, this disclosure may refer
to the border pixel indicated by the first pixel indicator as the
first current border pixel. For instance, in the example of FIG. 2,
if the first current border pixel is border pixel B, the video
coder may update the first pixel indicator to indicate border pixel
A. If the first current border pixel is border pixel R, the video
coder may update the first pixel indicator to indicate border pixel
I. If the first current border pixel is border pixel I, the video
coder may update the first pixel indicator to indicate border pixel
J.
[0168] After updating the first pixel indicator, the video coder
may determine whether the first current border pixel is available
(366). The video coder may determine whether the first current
border pixel is available in various ways. For example, the video
coder may perform the example operation of FIG. 13 to determine
whether the first current border pixel is available.
[0169] In response to determining that the first current border
pixel is unavailable ("NO" of 366), the video coder may assign the
value of the previous border pixel to the first current border
pixel (368). For instance, in the example of FIG. 2, if the first
current border pixel is border pixel I and border pixel I is
unavailable, the video coder may assign the value of border pixel R
to border pixel I. If the first current border pixel is border
pixel J and border pixel J is unavailable, the video coder may
assign the value of border pixel I to border pixel J, and so
on.
[0170] Once the video coder has assigned the value of the previous
border pixel to the first current border pixel or after determining
that the first current border pixel is available ("YES" of 366),
the video coder may determine whether the first current border
pixel is the bottom-left border pixel (370). In response to
determining that the first current border pixel is the bottom-left
border pixel ("YES" of 370), the video coder may end padding
operation 300 with regard to border pixels occurring left of or
below the current division point. However, in response to
determining that the first current border pixel is not the
bottom-left border pixel ("NO" of 370), the video coder may again
update the first pixel indicator (364) and perform steps 366-370
with regard to another border pixel. In this way, padding operation
350 may assign values to each unavailable border pixel left of or
below the current division point.
[0171] In addition, after setting the first and second pixel
indicators to the current division point in step 362, the video
coder may update the second pixel indicator to indicate a border
pixel that is above or to the right of the border pixel indicated
by the second pixel indicator (372). For ease of explanation, this
disclosure may refer to the border pixel indicated by the second
pixel indicator as the second current border pixel.
[0172] After updating the second pixel indicator, the video coder
may determine whether the second current border pixel is available
(374). The video coder may determine whether the second current
border pixel is available in various ways. For example, the video
coder may perform the example operation of FIG. 13 to determine
whether the second current border pixel is available.
[0173] In response to determining that the second current border
pixel is unavailable ("NO" of 374), the video coder may assign the
value of a previous border pixel to the second current border pixel
(376). For instance, in the example of FIG. 2, if the second
current border pixel is border pixel D and border pixel D is
unavailable, the video coder may assign the value of border pixel C
to border pixel D.
[0174] After assigning the value of a previous border pixel to the
second current border pixel or after the video coder has determined
that the second current border pixel is available ("YES" of 374),
the video coder may determine whether the second current border
pixel is the top-right border pixel (378). In response to
determining that the second current border pixel is the top-right
border pixel, the video coder may end padding operation 300 with
regard to border pixels that are to the right or above the current
division point. However, in response to determining that the second
current border pixel is not the top-right border pixel ("NO" of
378), the video coder may update the second pixel indicator (372)
and perform steps 374-378 with regard to another border pixel. In
this way, the video coder may process each border pixel that is
above or to the right of the division point border pixel.
[0175] In the example of FIG. 11, the video coder may perform steps
364-370 and steps 372-378 in parallel. In other examples, the video
coder may perform steps 364-370 and steps 372-378 sequentially.
[0176] FIG. 12 is a conceptual diagram that an example order in
which the padding operation of FIG. 11 proceeds through border
pixels. As illustrated in the example of FIG. 12, the shaded border
pixels are candidate division points. In the example of FIG. 12,
border pixel 400 may be the selected division point and the video
coder may concurrently process border pixels below the selected
division point (e.g., in steps 364-370 of FIG. 11) and border
pixels above and to the right of the selected division point (e.g.,
steps 372-378).
[0177] FIG. 13 is a flowchart that illustrates an example operation
450 to determine whether a border pixel is available. A video
coder, such as video encoder 20 or video decoder 30, may perform
operation 450. In other examples, the video coder may use
operations other than operation 450 to determine whether a border
pixel is available. For instance, in other examples, the video
coder may perform an operation in which the video coder performs
more, fewer, or different steps than operation 450.
[0178] After a video coder starts operation 450, the video coder
may determine whether the border pixel is outside a border of a
current picture (452). The current picture may be the picture that
the video coder is currently coding. For instance, if the video
coder is performing an intra-prediction operation for a PU whose
video block is adjacent to a top or left edge of the current
picture, one or more pixels above or to the left of the video block
may be outside the border of the current picture. In response to
determining that the border pixel is outside the border of the
current picture ("YES" of 452), the video coder may determine that
the border pixel is unavailable (454).
[0179] In response to determining that the border pixel is not
outside the border of the current picture ("NO" of 452), the video
coder may determine whether the border pixel is outside a border of
a current slice or tile and cross-slice/cross-tile prediction is
disallowed (456). The current slice or tile may be the slice or
tile that the video coder is currently coding. For instance, if the
video coder is performing an intra-prediction operation for a PU
whose video block is adjacent to a top or left edge of the current
slice or tile, one or more pixels above or to the left of the video
block may be outside the border of the current slice or tile. If
cross-slice prediction is allowed, the video coder is allowed to
use values of pixels in a first slice to generate an
intra-predicted video block for a CU in a second slice. In response
to determining that the border pixel is outside the border of the
current slice or tile and that cross-slice/tile prediction is
disallowed ("YES" of 456), the video coder may determine that the
border pixel is unavailable (454).
[0180] However, in response to determining that the border pixel is
not outside the current slice or tile or that
cross-slice/cross-tile prediction is allowed ("NO" of 456), the
video coder may determine whether the border pixel is associated
with an inter-predicted CU and whether constrained intra-prediction
is enabled (458). In other words, if the border pixel belongs to an
inter-predicted CU and constrained intra-prediction is enabled, the
border pixel may be marked as not available or unavailable. The
border pixel may be associated with an inter-predicted CU if the
border pixel is in a video block associated with an inter-predicted
CU.
[0181] In H.264/AVC, a macroblock (MB) in an inter-predicted slice
may be either coded as inter MB or intra MB. Similarly, in HEVC, a
CU in a P slice or a B slice may be an inter-predicted CU or an
intra-predicted CU. Intra MBs and intra-predicted CUs are predicted
from neighboring video blocks. In addition, a video coder may code
constrained intra MBs. A video coder may generate a constrained
intra MB from neighboring intra MBs in the same slice. In
accordance with the techniques of this disclosure, a video coder
may generate a constrained intra-predicted CU from video blocks of
neighboring intra-predicted CUs, but not video blocks of
neighboring inter-predicted CUs. A constrained_intra_pred_flag may
be signaled in a picture parameter set (PPS) to specify whether a
group of pictures are being coded with the only inter and
constrained intra modes.
[0182] Intra refresh may be an error resilience tool that enables a
video encoder to insert intra MBs or intra-predicted CUs in order
to reduce error propagation. In the event that a reference picture
is lost, a video decoder may be unable to correctly decode inter
MBs or inter-predicted CUs that use the reference picture. If the
inter MBs or inter-predicted CUs are used to predict an intra MB or
an intra-predicted CU, the video coder may be unable to decode the
intra MB or the intra-predicted CU. Thus, the error may be
propagated to the intra MB or the intra-predicted CU. Because
constrained intra MBs and constrained intra-predicted CUs do not
rely on inter MBs or inter-predicted CUs, the loss of the reference
picture does not prevent a video decoder from decoding the
constrained intra MBs or the intra-predicted CUs. Hence, it may be
more error resilient to code the intra MBs or intra-predicted CUs
as constrained intra MBs or constrained intra-predicted CUs.
[0183] In scalable video coding (SVC), a video decoder may not
fully decode multiple dependency layers (with the same or different
resolutions) because of the single-loop decoding design of the
video decoder. In this case, when an intra-predicted base layer
(BL) mode is used, the video decoder may only correctly decode
enhancement layer MBs if the corresponding base layer intra MBs are
coded as constrained intra MBs. Otherwise, the video decoder may
need to predict the base layer intra MBs from reconstructed
neighboring Inter MBs, which may not be available when decoding the
enhancement layer in case of single-loop decoding.
[0184] In response to determining that the border pixel is
associated with an inter-predicted CU and that constrained
intra-prediction is enabled ("YES" of 458), the video coder may
determine that the border pixel is unavailable (454). On the other
hand, in response to determining that the border pixel is not
associated with an inter-predicted CU or that constrained
intra-prediction is not enabled ("NO" of 458), the video coder may
determine that the border pixel is available (460).
[0185] In the examples above, a video coder may assign a default
value or a value of previous border pixel to unavailable border
pixels. In other examples, the video coder may interpolate values
of unavailable border pixels. For instance, if there are one or
more available border pixels on either side of a series of one or
more unavailable border pixels. In this instance, the video coder
may interpolate the values of the unavailable border pixels based
on the values of the available border pixels on either side of the
series of unavailable border pixels. The unavailable border pixels
may be interpolated as U.sub.i=A.sub.a+i*(A.sub.b-A.sub.a)/(M+1), i
from 1 to M. In this equation, A.sub.a and A.sub.b are the
available border pixels on either side of the series of unavailable
border pixels, M is the number of unavailable border pixels in the
series of unavailable border pixels, and U.sub.i indicates the
unavailable border pixels. In the equation above M might not be a
power of 2, so division may be needed.
[0186] Because M might not be a power of 2 and it may be desirable
to avoid division, another technique may be used to interpolate the
series of unavailable border pixels. According to this technique,
let Q=Floor(log.sub.2(M)), P=(1<<Q) and R=M-P. The video
coder may set each of the unavailable border pixels in the right,
which are U.sub.p+1 to U.sub.M, to the value of value of A.sub.b.
For any border pixel from U.sub.1 to U.sub.P,
U.sub.i=(A.sub.a*i+A.sub.b*(P-i)+P>>1)>>Q, i from 1 to
P.
[0187] In some instances there are not available border on either
side of a series of one or more unavailable border pixels. For
example, consecutive unavailable border pixels may occur from until
the end of the predictor. In this example, the video encoder may
extend the value of the last available border pixel to the end of
the predictor. In another example, consecutive unavailable border
pixels may occur at the start of a predictor. In this example, the
video coder may use the value of the first available border pixel
as the value of the unavailable border pixels preceding the first
available border pixel. Thus, in such instances, the video coder
may use simple extension to generate the values for the unavailable
reference samples.
[0188] 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.
[0189] 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.
[0190] 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.
[0191] 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.
[0192] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *