U.S. patent application number 13/869253 was filed with the patent office on 2017-10-05 for block artifact suppression in video coding.
This patent application is currently assigned to Texas Instruments Incorporated. The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to Madhukar Budagavi, Do-Kyoung Kwon.
Application Number | 20170289540 13/869253 |
Document ID | / |
Family ID | 49477259 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170289540 |
Kind Code |
A9 |
Kwon; Do-Kyoung ; et
al. |
October 5, 2017 |
Block Artifact Suppression in Video Coding
Abstract
A method for encoding a video sequence in a video encoder is
provided that includes adapting a quantization parameter of a block
of pixels in a picture of the video sequence based on a transform
block size of the block of pixels to determine a final quantization
parameter, and quantizing transform coefficients of the block of
pixels using the final quantization parameter.
Inventors: |
Kwon; Do-Kyoung; (Allen,
TX) ; Budagavi; Madhukar; (Plano, TX) |
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Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130287099 A1 |
October 31, 2013 |
|
|
Family ID: |
49477259 |
Appl. No.: |
13/869253 |
Filed: |
April 24, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13093715 |
Apr 25, 2011 |
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13869253 |
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12951035 |
Nov 20, 2010 |
8817884 |
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13093715 |
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61638248 |
Apr 25, 2012 |
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61642002 |
May 3, 2012 |
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61331216 |
May 4, 2010 |
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61431889 |
Jan 12, 2011 |
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61469518 |
Mar 30, 2011 |
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61262960 |
Nov 20, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 19/126 20141101;
H04N 19/20 20141101; H04N 19/157 20141101; H04N 19/86 20141101;
H04N 19/176 20141101; H04N 19/14 20141101 |
International
Class: |
H04N 7/26 20060101
H04N007/26 |
Claims
1. A method for encoding a video sequence in a video encoder, the
method comprising: adapting a quantization parameter of a block of
pixels in a picture of the video sequence based on a transform
block size of the block of pixels to determine a final quantization
parameter; and quantizing transform coefficients of the block of
pixels using the final quantization parameter.
2. The method of claim 1, wherein adapting a quantization parameter
comprises: computing an activity measure for the block of pixels;
adapting a base quantization parameter of the block of pixels based
on the activity measure to determine the quantization parameter;
determining a delta value for further adapting of the quantization
parameter, wherein the delta value is determined based on the
transform block size of the block of pixels; and adapting the
quantization parameter based on the delta value to determine the
final quantization parameter.
3. The method of claim 2, wherein a delta value for a largest
transform block size is non-zero and delta values for all other
transform block sizes are zero.
4. The method of claim 3, wherein the largest transform block size
is 32.times.32.
5. The method of claim 2, wherein a first delta value for a largest
transform block size is non-zero, and a second delta value for a
transform block size smaller than the largest transform block size
is non-zero, wherein the first delta value is larger than the
second delta value.
6. An apparatus for encoding a video sequence, the apparatus
comprising: means for adapting a quantization parameter of a block
of pixels in a picture of the video sequence based on a transform
block size of the block of pixels to determine a final quantization
parameter; and means for quantizing transform coefficients of the
block of pixels using the final quantization parameter.
7. The apparatus of claim 6, wherein the means for adapting a
quantization parameter: computes an activity measure for the block
of pixels; adapts a base quantization parameter of the block of
pixels based on the activity measure to determine the quantization
parameter; determines a delta value for further adapting of the
quantization parameter, wherein the delta value is determined based
on the transform block size of the block of pixels; and adapts the
quantization parameter based on the delta value to determine the
final quantization parameter.
8. The apparatus of claim 7, wherein a delta value for a largest
transform block size is non-zero and delta values for all other
transform block sizes are zero.
9. The apparatus of claim 8, wherein the largest transform block
size is 32.times.32.
10. The apparatus of claim 7, wherein a first delta value for a
largest transform block size is non-zero, and a second delta value
for a transform block size smaller than the largest transform block
size is non-zero, wherein the first delta value is larger than the
second delta value.
11. A non-transitory computer readable medium storing software
instructions that, when executed by a processor, cause a method for
encoding a video sequence to be performed, the method comprising:
adapting a quantization parameter of a block of pixels in a picture
of the video sequence based on a transform block size of the block
of pixels to determine a final quantization parameter; and
quantizing transform coefficients of the block of pixels using the
final quantization parameter.
12. The non-transitory computer readable medium of claim 11,
wherein adapting a quantization parameter comprises: computing an
activity measure for the block of pixels; adapting a base
quantization parameter of the block of pixels based on the activity
measure to determine the quantization parameter; determining a
delta value for further adapting of the quantization parameter,
wherein the delta value is determined based on the transform block
size of the block of pixels; and adapting the quantization
parameter based on the delta value to determine the final
quantization parameter.
13. The non-transitory computer readable medium of claim 12,
wherein a delta value for a largest transform block size is
non-zero and delta values for all other transform block sizes are
zero.
14. The non-transitory computer readable medium of claim 13,
wherein the largest transform block size is 32.times.32.
15. The non-transitory computer readable medium of claim 12,
wherein a first delta value for a largest transform block size is
non-zero, and a second delta value for a transform block size
smaller than the largest transform block size is non-zero, wherein
the first delta value is larger than the second delta value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional Patent
Application Ser. No. 61/638,248, filed Apr. 25, 2012, and U.S.
Provisional Patent Application Ser. No. 61/642,002, filed May 3,
2012, which are incorporated herein by reference in their
entirety.
[0002] This application may be related to United States Patent
Application Publication No. 2011/0122942, filed Nov. 20, 2010,
which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] Embodiments of the present invention generally relate to
block artifact suppression in video coding.
[0005] 2. Description of the Related Art
[0006] Video compression, i.e., video coding, is an essential
enabler for digital video products as it enables the storage and
transmission of digital video. In general, video compression
techniques apply prediction, transformation, quantization, and
entropy coding to sequential blocks of pixels in a video sequence
to compress, i.e., encode, the video sequence. Video decompression
techniques generally perform the inverse of these operations in
reverse order to decompress, i.e., decode, a compressed video
sequence.
[0007] The Joint Collaborative Team on Video Coding (JCT-VC) of
ITU-T WP3/16 and ISO/IEC JTC 1/SC 29/WG 11 is currently developing
the next-generation video coding standard referred to as High
Efficiency Video Coding (HEVC). HEVC is expected to provide around
45% improvement in coding efficiency over the current standard,
H.264/AVC, as well as larger resolutions and higher frame rates.
The improved coding efficiency is in part due to advanced intra and
inter prediction techniques with a large coding unit (LCU) of up to
64'64 in size, large transform units (TU) up to 32.times.32 in
size, rate-distortion optimized quantization, and improved loop
filtering including deblocking filtering and sample adaptive offset
(SAO), filtering. Even though both objective and subjective quality
is significantly improved, some annoying visual artifacts are
introduced. One such artifact is strong blockiness around
32.times.32 TU boundaries when high frequency transform
coefficients are coarsely quantized.
SUMMARY
[0008] Embodiments of the present invention relate to methods,
apparatus, and computer-readable media for block artifact
suppression in video coding. In one aspect, a method for encoding a
video sequence in a video encoder is provided that includes
adapting a quantization parameter of a block of pixels in a picture
of the video sequence based on a transform block size of the block
of pixels to determine a final quantization parameter, and
quantizing transform coefficients of the block of pixels using the
final quantization parameter.
[0009] In one aspect, an apparatus for encoding a video sequence is
provided that includes means for adapting a quantization parameter
of a block of pixels in a picture of the video sequence based on a
transform block size of the block of pixels to determine a final
quantization parameter, and means for quantizing transform
coefficients of the block of pixels using the final quantization
parameter.
[0010] In one aspect, a non-transitory computer readable medium
storing software instructions is provided. The software
instructions, when executed by a processor, cause a method for
encoding a video sequence to be performed that includes adapting a
quantization parameter of a block of pixels in a picture of the
video sequence based on a transform block size of the block of
pixels to determine a final quantization parameter, and quantizing
transform coefficients of the block of pixels using the final
quantization parameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Particular embodiments will now be described, by way of
example only, and with reference to the accompanying drawings:
[0012] FIG. 1 is an example;
[0013] FIG. 2 is a flow diagram of a prior art method for
perceptual quantization;
[0014] FIG. 3 is a block diagram of a digital system;
[0015] FIG. 4 is a block diagram of a video encoder;
[0016] FIG. 5 is a flow diagram of a method; and
[0017] FIG. 6 is a block diagram of an illustrative digital
system.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0018] Specific embodiments of the invention will now be described
in detail with reference to the accompanying figures. Like elements
in the various figures are denoted by like reference numerals for
consistency.
[0019] As used herein, the term "picture" may refer to a frame or a
field of a frame. A frame is a complete image captured during a
known time interval. For convenience of description, embodiments
are described herein in reference to HEVC. One of ordinary skill in
the art will understand that embodiments of the invention are not
limited to HEVC.
[0020] As used herein, the term `activity` refers to the extent of
variation in the values of pixels contained in a block of video
data. Thus, in general, a block with higher `activity` has greater
variation in pixel values, and will have more higher-frequency
components (in terms of variation in the pixel values) than
low-frequency components. In contrast, a block with lower
`activity` has lesser variation in pixel values, and will have more
low-frequency components than high-frequency components.
[0021] In HEVC, a largest coding unit (LCU) is the base unit used
for block-based coding. A picture is divided into non-overlapping
LCUs. That is, an LCU plays a similar role in coding as the
macroblock of H.264/AVC, but it may be larger, e.g., 32.times.32,
64.times.64, etc. An LCU may be partitioned into coding units (CU).
A CU is a block of pixels within an LCU and the CUs within an LCU
may be of different sizes. The partitioning is a recursive quadtree
partitioning. The quadtree is split according to various criteria
until a leaf is reached, which is referred to as the coding node or
coding unit. The maximum hierarchical depth of the quadtree is
determined by the size of the smallest CU (SCU) permitted. The
coding node is the root node of two trees, a prediction tree and a
transform tree. A prediction tree specifies the position and size
of prediction units (PU) for a coding unit. A transform tree
specifies the position and size of transform units (TU) for a
coding unit. A transform unit may not be larger than a coding unit
and the size of a transform unit may be, for example, 4.times.4,
8.times.8, 16.times.16, and 32.times.32. The sizes of the
transforms units and prediction units for a CU are determined by
the video encoder during prediction based on minimization of
rate/distortion costs.
[0022] Various versions of HEVC are described in the following
documents, which are incorporated by reference herein: T. Wiegand,
et al., "WD3: Working Draft 3 of High-Efficiency Video Coding,"
JCTVC-E603, Joint Collaborative Team on Video Coding (JCT-VC) of
ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Geneva, CH, Mar. 16-23,
2011 ("WD3"), B. Bross, et al., "WD4: Working Draft 4 of
High-Efficiency Video Coding," JCTVC-F803_d6, Joint Collaborative
Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC
JTC1/SC29/WG11, Torino, IT, July 14-22, 2011 ("WD4"), B. Bross. et
al., "WD5: Working Draft 5 of High-Efficiency Video Coding,"
JCTVC-G1103_d9, Joint Collaborative Team on Video Coding (JCT-VC)
of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, Geneva, CH, Nov.
21-30, 2011 ("WD5"), B. Bross, et al., "High Efficiency Video
Coding (HEVC) Text Specification Draft 6," JCTVC-H1003, Joint
Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and
ISO/IEC JTC1/SC29/WG1, Geneva, CH, Nov. 21-30, 2011 ("HEVC Draft
6"), B. Bross, et al., "High Efficiency Video Coding (HEVC) Text
Specification Draft 7," JCTVC-11003_d0, Joint Collaborative Team on
Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1,
Geneva, CH, April 27-May 7, 2012 ("HEVC Draft 7"), B. Bross, et
al., "High Efficiency Video Coding (HEVC) Text Specification Draft
8," JCTVC-J1003_d7, Joint Collaborative Team on Video Coding
(JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1, Stockholm,
SE, Jul. 11-20, 2012 ("HEVC Draft 8"), and B. Bross, et al., "High
Efficiency Video Coding (HEVC) Text Specification Draft 9,"
JCTVC-K1003_v7, Joint Collaborative Team on Video Coding (JCT-VC)
of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG1, Shanghai, CN, Oct.
10-19, 2012 ("HEVC Draft 9").
[0023] As previously discussed, strong block artifacts are observed
around 32.times.32 TU boundaries when high frequency transform
coefficients are coarsely quantized. This may occur because coarser
quantization for this TU size can increase any discontinuities from
neighboring TUs. FIG. 1 is an example illustrating strong blocking
artifacts at 32.times.32 TU boundaries.
[0024] One well known way to improve visual quality (and reduce
blocking artifacts) that has been used in H.264/AVC is perceptual
quantization (sometimes also referred to as adaptive quantization).
In perceptual quantization, the quantization parameter (QP) values
for blocks in a frame are varied to distribute the noise and
artifacts according to masking properties of the human visual
system (HVS). The goal is to maximize the visual quality of an
encoded video sequence while keeping the bit rate low. For example,
according to HVS theory, the human visual system performs texture
masking (also called detail dependence, spatial masking or activity
masking). That is, the discrimination threshold of the human eye
increases with increasing picture detail, making the human eye less
sensitive to quantization noise and coding artifacts in busy or
highly textured portions of frames and more sensitive in flat or
low-textured portions.
[0025] During video encoding, this texture masking property of the
HVS can be exploited by shaping the quantization noise in the video
frame based on the texture content (also referred to as activity)
in the different parts of the video frame. More specifically, the
quantization step size can be increased in highly textured
portions, resulting in coarser quantization and a lower bit rate
requirement, and can be decreased in low-textured or flat portions
to maintain or improve video quality, resulting in finer
quantization but a higher bit rate requirement. The human eye will
perceive a "noise-shaped" video frame as having better subjective
quality than a video frame which has the same amount of noise
evenly distributed throughout the video frame.
[0026] FIG. 2 illustrates a typical prior art technique for
perceptual quantization as used in H.264/AVC. For each macroblock,
a block activity measure (act) is computed. A decision is then made
based on the block activity measure as to whether or not the base
quantization parameter (base QP) as determined by rate control for
the macroblock is to be changed, and if it is to be changed, by how
much. For example, in macroblocks with high activity measures, the
base QP may be increased to reduce bit rate as typically coding
artifacts are less visible in such complex areas. In macroblocks
with low activity measures, which is indicative of a smooth area in
which coding artifacts may be more visible, the base QP may be
reduced to improve visual quality. U.S. Pat. App. Pub. No.
2011/0122942 describes various embodiments of this prior technique
for perceptual quantization, along with various methods for
measuring macroblock activity and modulating base QP based on the
measured activity.
[0027] Embodiments of the invention provide for perceptual
quantization that determines quantization parameters for coding
units based both on CU activity measures and transform unit (TU)
size. More specifically, for a CU with the largest TU size, e.g.,
32.times.32, the base quantization parameter may be modulated
(adapted) based on activity measured in the CU and based on the TU
size. Consideration of the TU size allows the QP for CUs having the
largest TU size, e.g., 32.times.32, to be decreased (made less
coarse) to suppress discontinuities from neighboring CUs and thus
decrease blocking artifacts.
[0028] FIG. 3 shows a block diagram of a digital system that
includes a source digital system 300 that transmits encoded video
sequences to a destination digital system 302 via a communication
channel 316. The source digital system 300 includes a video capture
component 304, a video encoder component 306, and a transmitter
component 308. The video capture component 304 is configured to
provide a video sequence to be encoded by the video encoder
component 306. The video capture component 304 may be, for example,
a video camera, a video archive, or a video feed from a video
content provider. In some embodiments, the video capture component
304 may generate computer graphics as the video sequence, or a
combination of live video, archived video, and/or
computer-generated video.
[0029] The video encoder component 306 receives a video sequence
from the video capture component 304 and encodes it for
transmission by the transmitter component 308. The video encoder
component 306 receives the video sequence from the video capture
component 304 as a sequence of pictures, divides the pictures into
largest coding units (LCUs), and encodes the video data in the
LCUs. The video encoder component 306 may be configured to perform
a method for determining quantization parameters based on transform
unit size during the encoding process as described herein. An
embodiment of the video encoder component 306 is described in more
detail herein in reference to FIG. 4.
[0030] The transmitter component 308 transmits the encoded video
data to the destination digital system 302 via the communication
channel 316. The communication channel 316 may be any communication
medium, or combination of communication media suitable for
transmission of the encoded video sequence, such as, for example,
wired or wireless communication media, a local area network, or a
wide area network.
[0031] The destination digital system 302 includes a receiver
component 310, a video decoder component 312 and a display
component 314. The receiver component 310 receives the encoded
video data from the source digital system 300 via the communication
channel 316 and provides the encoded video data to the video
decoder component 312 for decoding. The video decoder component 312
reverses the encoding process performed by the video encoder
component 306 to reconstruct the LCUs of the video sequence.
[0032] The reconstructed video sequence is displayed on the display
component 314. The display component 314 may be any suitable
display device such as, for example, a plasma display, a liquid
crystal display (LCD), a light emitting diode (LED) display,
etc.
[0033] In some embodiments, the source digital system 300 may also
include a receiver component and a video decoder component and/or
the destination digital system 302 may include a transmitter
component and a video encoder component for transmission of video
sequences both directions for video streaming, video broadcasting,
and video telephony. Further, the video encoder component 306 and
the video decoder component 312 may perform encoding and decoding
in accordance with one or more video compression standards. The
video encoder component 306 and the video decoder component 312 may
be implemented in any suitable combination of software, firmware,
and hardware, such as, for example, one or more digital signal
processors (DSPs), microprocessors, discrete logic, application
specific integrated circuits (ASICs), field-programmable gate
arrays (FPGAs), etc.
[0034] FIG. 4 is a block diagram of the LCU processing portion of
an example video encoder, e.g., the video encoder component of FIG.
3, with functionality to determine quantization parameters for CUs
based on TU size in the CU. An input digital video sequence is
provided to a coding control component (not shown), e.g., from a
video capture component 304 (see FIG. 3). The coding control
component sequences the various operations of the video encoder,
i.e., the coding control component runs the main control loop for
video encoding. For example, the coding control component performs
processing on the input video sequence that is to be done at the
picture level, such as determining the coding type (I, P, or B) of
a picture based on a high level coding structure, e.g., IPPP, IBBP,
hierarchical-B, and dividing a picture into LCUs for further
processing.
[0035] In addition, for pipelined architectures in which multiple
LCUs may be processed concurrently in different components of the
LCU processing, the coding control component controls the
processing of the LCUs by various components of the LCU processing
in a pipeline fashion. For example, in many embedded systems
supporting video processing, there may be one master processor and
one or more slave processing modules, e.g., hardware accelerators.
The master processor operates as the coding control component and
runs the main control loop for video encoding, and the slave
processing modules are employed to off load certain
compute-intensive tasks of video encoding such as motion
estimation, motion compensation, intra prediction mode estimation,
transformation and quantization, entropy coding, and loop
filtering. The slave processing modules are controlled in a
pipeline fashion by the master processor such that the slave
processing modules operate on different LCUs of a picture at any
given time. That is, the slave processing modules are executed in
parallel, each processing its respective LCU while data movement
from one processor to another is serial.
[0036] The coding control component includes functionality to
perform rate control for generation of the compressed bit stream.
As part of rate control, the coding control component generates
base quantization parameters (base QPs) to be used for quantization
of the transform coefficients of coding units. Any suitable
technique for rate control may be used. As is explained in more
detail herein, the quantization component 406 may adapt the base
quantization parameter based on activity (texture) measured in a CU
and on TU size in the CU.
[0037] The LCU processing receives LCUs 400 of the input video
sequence from the coding control component and encodes the LCUs 400
under the control of the coding control component to generate the
compressed video stream. The LCUs 400 in each picture are processed
in row order. The LCUs 400 from the coding control component are
provided as one input of a motion estimation component (ME) 420, as
one input of an intra-prediction estimation component (IPE) 424,
and to a positive input of a combiner 402 (e.g., adder or
subtractor or the like). Further, although not specifically shown,
the prediction mode of each picture as selected by the coding
control component is provided to a mode decision component 428 and
the entropy coding component 436.
[0038] The storage component 418 provides reference data to the
motion estimation component 420 and to the motion compensation
component 422. The reference data may include one or more
previously encoded and decoded pictures, i.e., reference
pictures.
[0039] The motion estimation component 420 provides motion data
information to the motion compensation component 422 and the
entropy coding component 436. More specifically, the motion
estimation component 420 performs tests on CUs in an LCU based on
multiple inter-prediction modes (e.g., skip mode, merge mode, and
normal or direct inter-prediction), PU sizes, and TU sizes using
reference picture data from storage 418 to choose the best CU
partitioning, PU/TU partitioning, inter-prediction modes, motion
vectors, etc. based on coding cost, e.g., a rate distortion coding
cost. To perform the tests, the motion estimation component 420 may
divide an LCU into CUs according to the maximum hierarchical depth
of the quadtree, and divide each CU into PUs according to the unit
sizes of the inter-prediction modes and into TUs according to the
transform unit sizes, and calculate the coding costs for each PU
size, prediction mode, and transform unit size for each CU. The
motion estimation component 420 provides the motion vector (MV) or
vectors and the prediction mode for each PU in the selected CU
partitioning to the motion compensation component (MC) 422.
[0040] The motion compensation component 422 receives the selected
inter-prediction mode and mode-related information from the motion
estimation component 420 and generates the inter-predicted CUs. The
inter-predicted CUs are provided to the mode decision component 428
along with the selected inter-prediction modes for the
inter-predicted PUs and corresponding TU sizes for the selected
CU/PU/TU partitioning. The coding costs of the inter-predicted CUs
are also provided to the mode decision component 428.
[0041] The intra-prediction estimation component 424 (IPE) performs
intra-prediction estimation in which tests on CUs in an LCU based
on multiple intra-prediction modes, PU sizes, and TU sizes are
performed using reconstructed data from previously encoded
neighboring CUs stored in a buffer (not shown) to choose the best
CU partitioning, PU/TU partitioning, and intra-prediction modes
based on coding cost, e.g., a rate distortion coding cost. To
perform the tests, the intra-prediction estimation component 424
may divide an LCU into CUs according to the maximum hierarchical
depth of the quadtree, and divide each CU into PUs according to the
unit sizes of the intra-prediction modes and into TUs according to
the transform unit sizes, and calculate the coding costs for each
PU size, prediction mode, and transform unit size for each PU. The
intra-prediction estimation component 424 provides the selected
intra-prediction modes for the PUs, and the corresponding TU sizes
for the selected CU partitioning to the intra-prediction component
(IP) 426. The coding costs of the intra-predicted CUs are also
provided to the intra-prediction component 426.
[0042] The intra-prediction component 426 (IP) receives
intra-prediction information, e.g., the selected mode or modes for
the PU(s), the PU size, etc., from the intra-prediction estimation
component 424 and generates the intra-predicted CUs. The
intra-predicted CUs are provided to the mode decision component 428
along with the selected intra-prediction modes for the
intra-predicted PUs and corresponding TU sizes for the selected
CU/PU/TU partitioning. The coding costs of the intra-predicted CUs
are also provided to the mode decision component 428.
[0043] The mode decision component 428 selects between
intra-prediction of a CU and inter-prediction of a CU based on the
intra-prediction coding cost of the CU from the intra-prediction
component 426, the inter-prediction coding cost of the CU from the
motion compensation component 422, and the picture prediction mode
provided by the coding control component. Based on the decision as
to whether a CU is to be intra- or inter-coded, the intra-predicted
PUs or inter-predicted PUs are selected. The selected CU/PU/TU
partitioning with corresponding modes and other mode related
prediction data (if any) such as motion vector(s) and reference
picture index (indices), are provided to the entropy coding
component 436.
[0044] The output of the mode decision component 428, i.e., the
predicted PUs, is provided to a negative input of the combiner 402
and to the combiner 438. The associated transform unit size is also
provided to the transform component 404. The combiner 402 subtracts
a predicted PU from the original PU. Each resulting residual PU is
a set of pixel difference values that quantify differences between
pixel values of the original PU and the predicted PU. The residual
blocks of all the PUs of a CU form a residual CU for further
processing.
[0045] The transform component 404 performs block transforms on the
residual CUs to convert the residual pixel values to transform
coefficients and provides the transform coefficients to a
quantization component 406. More specifically, the transform
component 404 receives the transform unit sizes for the residual CU
and applies transforms of the specified sizes to the CU to generate
transform coefficients. Further, the quantization component 406
quantizes the transform coefficients based on base quantization
parameters (base QPs) provided by the coding control component and
the transform sizes and provides the quantized transform
coefficients to the entropy coding component 436 for coding in the
bit stream. To determine the actual quantization parameter for a
CU, the quantization component 406 may adapt (modulate) the base QP
based on activity (texture) in the CU and based on the TU size used
for the CU. A method for modulating base QP based on activity and
TU size that may be performed by the quantization component 406 is
described herein in reference to FIG. 5.
[0046] The entropy coding component 436 entropy encodes the
relevant data, i.e., syntax elements, output by the various
encoding components and the coding control component using
context-adaptive binary arithmetic coding (CABAC) to generate the
compressed video bit stream. Among the syntax elements that are
encoded are picture parameter sets, flags indicating the CU/PU/TU
partitioning of an LCU, the prediction modes for the CUs,
quantization information, and the quantized transform coefficients
for the CUs. The entropy coding component 436 also codes relevant
data from the in-loop filters (described below).
[0047] The LCU processing includes an embedded decoder. As any
compliant decoder is expected to reconstruct an image from a
compressed bit stream, the embedded decoder provides the same
utility to the video encoder. Knowledge of the reconstructed input
allows the video encoder to transmit the appropriate residual
energy to compose subsequent pictures and to compute checksums to
be included in hash SEI message in the compressed bit stream.
[0048] The quantized transform coefficients for each CU are
provided to an inverse quantization component (IQ) 412, which
outputs a reconstructed version of the transform result from the
transform component 404. The dequantized transform coefficients are
provided to the inverse transform component (IDCT) 414, which
outputs estimated residual information representing a reconstructed
version of a residual CU. The inverse transform component 414
receives the transform unit size used to generate the transform
coefficients and applies inverse transform(s) of the specified size
to the transform coefficients to reconstruct the residual values.
The reconstructed residual CU is provided to the combiner 438.
[0049] The combiner 438 adds the original predicted CU to the
residual CU to generate a reconstructed CU, which becomes part of
reconstructed picture data. The reconstructed picture data is
stored in a buffer (not shown) for use by the intra-prediction
estimation component 424.
[0050] Various in-loop filters may be applied to the reconstructed
picture data to improve the quality of the reference picture data
used for encoding/decoding of subsequent pictures. The in-loop
filters may include a deblocking filter component 430, a sample
adaptive offset filter (SAO) component 432, and an adaptive loop
filter (ALF) component 434. The in-loop filters 430, 432, 434 are
applied to each reconstructed LCU in the picture and the final
filtered reference picture data is provided to the storage
component 418. In some embodiments, the ALF filter component 434
may not be present.
[0051] FIG. 5 is a flow diagram of a method for adaptive
quantization in which a base quantization parameter (base QP) for a
coding unit is adapted (modulated) based on measured activity in
the CU and based on TU size in the CU. This method may be
performed, for example, by the quantization component 406 of FIG.
4. Initially, an activity measure for the coding unit is computed
500. The activity measure may be representative of the degree of
sensitivity of the human visual system to information in the CU,
i.e., may be representative of amount of texture in the CU. Any
suitable technique for computing the activity measure may be used.
Some suitable techniques that may are described in U.S. Pat. App.
Pub. No. 2011/0122942.
[0052] The base QP for the CU is then adapted 502 to QP' based on
the computed activity measure. In general, if the activity measure
indicates that the amount of activity in the block is high, the
base QP is increased by some amount to reduce bit rate as typically
coding artifacts are less visible in more complex areas. Further,
if the activity measure indicates that the amount of activity in
the block is low, the base QP is decreased by some amount to
improve visual quality as coding artifacts may be more visible in
smoother areas. Any suitable technique for adapting the base QP
based on the activity measure may be used. Some suitable techniques
that may be used are described in U.S. Pat. App. Pub. No.
2011/0122942. Note that the base QP value may not always be
changed. However, for convenience of description, the output of
this step is referred to as QP' even if QP'=base QP.
[0053] A delta amount to be used to further adapt the value of QP'
is then determined 504 based on the size of the TUs in the CU. In
some embodiments, delta=0 for all TU sizes except the largest TU
size, e.g., 32.times.32. In such embodiments, the value of delta
for the largest TU size may be any suitable predetermined value.
For example, the value of delta for the largest TU size may be
empirically determined using a representative set of video
sequences that the encoder is designed to encode. The value of
delta for the largest TU size may be selected such that decreasing
QP' for CUs with TUs of this largest size by delta suppresses
discontinuities from neighboring CUs and thus decreases blocking
artifacts caused by using this largest TU size.
[0054] In some embodiments, the value of delta may be non-zero for
the largest TU size, and for one or more of the smaller TU sizes.
The delta values for the smaller TU sizes are smaller than that of
the largest TU sizes. For example, if the largest TU size is
32.times.32 and the next largest TU size is 16.times.16, the delta
values for both the 32.times.32 TU size and the 16.times.16 TU size
may be non-zero, with the delta value for the 16.times.16 TU size
being smaller than that of the 32.times.32 TU size. In such
embodiments, the value of delta for each of the TU sizes may be any
suitable predetermined values. For example, the values of delta for
each of the TU sizes may be empirically determined using a
representative set of video sequences that the encoder is designed
to encode.
[0055] QP' is then adapted 506 based on the value of delta to
produce the final QP value, i.e., QP=QP'+delta. This final QP value
is then use to quantize 508 the transform coefficients of the CU.
In some embodiments, to avoid abrupt changes in the final QP, the
value of the final QP is clipped to reduce the difference between
the final QP and the QP of the previous CU. Let the QP of the
previous CU be denoted as QPprev. The final QP may be clipped such
that |QP-Qprev|.ltoreq.d, i.e., if QP>QPprev+d, then QP is set
to QPprev+d, and if QP<QPprev-d, QP is set to QPprev-d. Any
suitable value of the distance d may be used.
[0056] Embodiments of the methods and encoders described herein may
be implemented for virtually any type of digital system (e.g., a
desk top computer, a laptop computer, a tablet computing device, a
netbook computer, a handheld device such as a mobile (i.e.,
cellular) phone, a personal digital assistant, a digital camera,
etc.). FIG. 6 is a block diagram of an example digital system
suitable for use as an embedded system that may be configured to
adapt (modulate) the base QPs of CUs based on activity (texture) in
the CUs and based on the TU size used for the CUs as described
herein during encoding of a video stream. This example
system-on-a-chip (SoC) is representative of one of a family of
DaVinci.TM. Digital Media Processors, available from Texas
Instruments, Inc. This SoC is described in more detail in
"TMS320DM6467 Digital Media System-on-Chip", SPRS403G, December
2007 or later, which is incorporated by reference herein.
[0057] The SoC 600 is a programmable platform designed to meet the
processing needs of applications such as video
encode/decode/transcode/transrate, video surveillance, video
conferencing, set-top box, medical imaging, media server, gaming,
digital signage, etc. The SoC 600 provides support for multiple
operating systems, multiple user interfaces, and high processing
performance through the flexibility of a fully integrated mixed
processor solution. The device combines multiple processing cores
with shared memory for programmable video and audio processing with
a highly-integrated peripheral set on common integrated
substrate.
[0058] The dual-core architecture of the SoC 600 provides benefits
of both DSP and Reduced Instruction Set Computer (RISC)
technologies, incorporating a DSP core and an ARM926EJ-S core. The
ARM926EJ-S is a 32-bit RISC processor core that performs 32-bit or
16-bit instructions and processes 32-bit, 16-bit, or 8-bit data.
The DSP core is a TMS320C64x+TM core with a
very-long-instruction-word (VLIW) architecture. In general, the ARM
is responsible for configuration and control of the SoC 600,
including the DSP Subsystem, the video data conversion engine
(VDCE), and a majority of the peripherals and external memories.
The switched central resource (SCR) is an interconnect system that
provides low-latency connectivity between master peripherals and
slave peripherals. The SCR is the decoding, routing, and
arbitration logic that enables the connection between multiple
masters and slaves that are connected to it.
[0059] The SoC 600 also includes application-specific hardware
logic, on-chip memory, and additional on-chip peripherals. The
peripheral set includes: a configurable video port (Video Port
I/F), an Ethernet MAC (EMAC) with a Management Data Input/Output
(MDIO) module, a 4-bit transfer/4-bit receive VLYNQ interface, an
inter-integrated circuit (I2C) bus interface, multichannel audio
serial ports (McASP), general-purpose timers, a watchdog timer, a
configurable host port interface (HPI); general-purpose
input/output (GPIO) with programmable interrupt/event generation
modes, multiplexed with other peripherals, UART interfaces with
modem interface signals, pulse width modulators (PWM), an ATA
interface, a peripheral component interface (PCI), and external
memory interfaces (EMIFA, DDR2). The video port I/F is a receiver
and transmitter of video data with two input channels and two
output channels that may be configured for standard definition
television (SDTV) video data, high definition television (HDTV)
video data, and raw video data capture.
[0060] As shown in FIG. 6, the SoC 600 includes two high-definition
video/imaging coprocessors (HDVICP) and a video data conversion
engine (VDCE) to offload many video and image processing tasks from
the DSP core. The VDCE supports video frame resizing,
anti-aliasing, chrominance signal format conversion, edge padding,
color blending, etc. The HDVICP coprocessors are designed to
perform computational operations required for video encoding such
as motion estimation, motion compensation, intra-prediction,
transformation, quantization, and in-loop filtering. Further, the
distinct circuitry in the HDVICP coprocessors that may be used for
specific computation operations is designed to operate in a
pipeline fashion under the control of the ARM subsystem and/or the
DSP subsystem.
[0061] As was previously mentioned, the SoC 600 may be configured
to adapt (modulate) the base QPs of CUs based on activity (texture)
in the CUs and based on the TU size used for the CUs as described
herein during encoding of a video stream described herein during
encoding of a video stream. For example, the coding control of the
video encoder of FIG. 4 may be executed on the DSP subsystem or the
ARM subsystem and at least some of the computational operations of
the block processing, including the intra-prediction and
inter-prediction of mode selection, transformation, quantization,
and entropy encoding may be executed on the HDVICP
coprocessors.
OTHER EMBODIMENTS
[0062] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein.
[0063] Embodiments of the methods, encoders, and decoders described
herein may be implemented in hardware, software, firmware, or any
combination thereof. If completely or partially implemented in
software, the software may be executed in one or more processors,
such as a microprocessor, application specific integrated circuit
(ASIC), field programmable gate array (FPGA), or digital signal
processor (DSP). The software instructions may be initially stored
in a computer-readable medium and loaded and executed in the
processor. In some cases, the software instructions may also be
sold in a computer program product, which includes the
computer-readable medium and packaging materials for the
computer-readable medium. In some cases, the software instructions
may be distributed via removable computer readable media, via a
transmission path from computer readable media on another digital
system, etc. Examples of computer-readable media include
non-writable storage media such as read-only memory devices,
writable storage media such as disks, flash memory, memory, or a
combination thereof.
[0064] Although method steps may be presented and described herein
in a sequential fashion, one or more of the steps shown in the
figures and described herein may be performed concurrently, may be
combined, and/or may be performed in a different order than the
order shown in the figures and/or described herein. Accordingly,
embodiments should not be considered limited to the specific
ordering of steps shown in the figures and/or described herein.
[0065] It is therefore contemplated that the appended claims will
cover any such modifications of the embodiments as fall within the
true scope of the invention.
* * * * *