FAST MODE DECISION ALGORITHM FOR INTRA
PREDICTION IN HEVC
LANKA NAGA VENKATA SAI SURYA TEJA
STUDENT ID: 1000916473
MAIL ID nvssurya.lanka@mavs.uta.edu
DATE : 03/24/2014
UNDER THE GUIDANCE OF
DR. K. R. RAO
EE 5359 MULTIMEDIA PROCESSING
UNIVERSITY OF TEXAS AT ARLINGTON
ACRONYMS:
BD- Bitrate - Bjøntegaard Delta Bitrate
BD- PSNR
CU
-
Bjøntegaard Delta Peak Signal-to-Noise Ratio
- Coding Unit
DCT - Discrete Cosine Transform
DST
- Discrete Sine Transform
HEVC - High Efficiency Video Coding
JCT- VC- Joint Collaborative Team on Video Coding
LCU - Largest Coding Unit
MPM - Most Probable Mode
PSNR - Peak Signal-to-Noise Ratio
PU
- Prediction Unit
RDOQ - Rate Distortion Optimization Quantization
RDO - Rate- Distortion Optimization
RMD - Rough Mode Decision
SSIM
- Structural Similarity Index
TU
- Transform Unit
PROPOSAL: To improve the coding efficiency of intra frame coding, up to 34 intra prediction
modes are defined in High Efficiency Video Coding (HEVC) [1]. The best mode among these
pre-defined intra prediction modes is selected by rate-distortion optimization (RDO) for each
block. This project proposes a new method to reduce the candidates in RDO process, as it will be
time-consuming if all directions are tested in the RDO process. Also in this project, it provides
20% and 28% time savings in intra high efficiency and low complexity cases on average
compared to the default encoding scheme in HM 13.0 [5] with almost the same coding
efficiency. Also analysis of PSNR, BD- PSNR, SSIM, BD- Bitrate can be done by comparing
with the default encoding scheme in HM 13.0 [5].
Index Terms: video coding, HEVC, intra prediction
INTRODUCTION: HEVC standard [2] provides a highly flexible hierarchy of unit
representation which consists of three block concepts: coding unit (CU), prediction unit (PU),
and transform unit (TU). This separation of the block structure is helpful for each unit of
optimization. CU is a macroblock-like unit of region splitting which is always square and its size
can be from 8x8 luma samples up to the largest coding units (LCUs). This concept allows
recursive splitting into four equal sized blocks, starting from LCU. This process gives a contentadaptive coding tree structure comprised of CU blocks. Figure 4 shows coding tree structure [3].
The PU is used only for the CU which is the leaf node in the Quadtree structure and the size of
two PUs are 2Nx2N and NxN. The third block concept transform unit size cannot exceed that of
the CU. Figure 1 shows the block diagram of H.264 encoder [20].
Figure 1: Block Diagram of H.264 Encoder [20]
Figure 2- Block diagram of HEVC encoder [15]
Figure 2 shows block diagram of HEVC Encoder [15] in which each picture is partitioned into
blocks of different sizes and the same is conveyed to the decoder. In the given sequence intra
prediction is applied to the very first picture which uses spatial redundancy of the picture while
for rest of the frames temporal redundancy is exploited using inter prediction. Since encoder
needs to exhaust all the combinations of CU, PU and TU to find the optimal solutions, it is very
time-consuming. The encoder will not tolerate it if all the directions are employed in the ratedistortion optimization process. To reduce the computational complexity of the encoder, a fast
intra mode decision [4] was adopted in HM 13.0 [5]. Figure 3 shows block diagram of HEVC
Decoder [15].
Figure 3- Block diagram of HEVC decoder [15]
(c)
(d)
Figure 4- Coding tree structure [3]
OVERVIEW OF INTRA PREDICTION IN HEVC: In H.264, intra prediction [6][7][8][9] is
based on spatial extrapolation of samples from previously decoded image blocks, followed by
integer discrete cosine transform (DCT) [10] based coding. HEVC utilizes the same principle,
but further extends it to efficiently represent wider range of textural and structural information in
images. HEVC contains several elements improving the efficiency of intra prediction over earlier
solutions. The introduced methods can model accurately different structures as well as smooth
regions with gradually changing sample values. Figure 4 shows the intra prediction modes of
HEVC [7] and figure 5 shows the intra prediction modes of H.264 [21].
Figure 4- HEVC intra prediction modes [7]
Figure 5: H.264 intra prediction modes [21]
Prediction size
64x64
32x32
16x16
8x8
4x4
Total Modes
Total Intra Angular modes
HEVC/H.265(64x64)
H.264/AVC(16x16)
4
35
35
35
18
7808
NA
NA
4
9
9
16x(16x9+4x9+4)=2944
Figure 6: Comparing HEVC Intra luma prediction modes for 64x64 LCU with H.264/AVC Intra
modes for a 64x64 image region [11]
METHOD PROPOSED FOR FAST MODE DECISON ALGORITHM FOR INTRA
PREDICTION: The fast intra prediction consists of three steps.
1 - Hadamard Transformed Coefficients Of Residual Signal [13]
2 - Progressive Mode Search [13]
3 - Early RDOQ Termination [13]
By combining these three steps, fast mode decision algorithm can be performed. The unified
intra in HM13.0 first determines the first N best candidate modes selected by a rough mode
decision (RMD) process where all modes are tested by minimum absolute sum of Hadamard
transformed coefficients of residual signal and the mode bits in the rough mode decision. Instead
of the total intra prediction modes decision, the RD optimization is only applied to the N best
candidate modes selected by the rough mode decision where all modes are compared in this
decision. However, computation load of the encoder is still very high. On the other side, the intra
prediction modes are always correlated among the neighbors which are not considered in HM
13.0. Therefore, there is still some room for further reducing the encoder complexity.
To further relieve the computation load of the encoder, it is important to reduce the candidates
for RDO process and make full use of the information of its neighboring blocks. In this project,
check for less number of best RMD modes for RDO, and the most probable mode (MPM) is
always included in the candidates for RDO.
TEST SEQUENCES USED:
[1] BQSquare_416x240_60 [16]
[2] BQMall_ 832x480_60 [16]
[3] KristenAndSara_1280x720_60 [16]
REFERENCES:
[1] G.J. Sullivan et al, Overview of the high efficiency video coding (HEVC) standard‖, IEEE
Trans. circuits and systems for video technology, vol. 22, no.12, pp. 1649 – 1668, Dec 2012.
[2] JCT-VC, “WD1: Working Draft 1 of High-Efficiency Video Coding”, JCTVC-C403, JCTVC Meeting, Guangzhou, October 2010.
[3] Coding tree structure - https://www.google.com/search?q=coding+tree+structure+in+hevc
[4] Y. Piao et al, “Encoder improvement of unified intra prediction,” JCTVC-C207, Guangzhou,
October 2010.
[5] Software for HEVC : https://hevc.hhi.fraunhofer.de/svn/svn_HEVCSoftware
[6] T.L. Silva et al, ”HEVC intra coding acceleration based on tree inter-level mode correlation”,
SPA 2013, Poznan, Poland, Sep.2013
[7] H. Zhang and Z. Ma, ”Fast intra prediction for high efficiency video coding ”, Pacific Rim
Conf. on Multimedia, PCM2012, Singapore, Dec. 2012.
[8] M. Zhang et al, ”An adaptive fast intra mode decision in HEVC ”, IEEE ICIP 2012, pp.221224, Orlando, FL, Sept.- Oct. 2012.
[9] Y. Kim et al, “A fast intra-prediction method in HEVC using rate-distortion estimation based
on Hadamard transform”, ETRI Journal, vol.35, #2, pp.270-280, Apr. 2013.
[10] A. Saxena and F. Fernanades, “Mode dependent DCT/DST for intra prediction in block
based image/video coding”, IEEE ICIP, pp. 1685-1688, Sept. 2011.
[11] M. Khan et al, “An adaptive complexity reduction scheme with fast prediction unit decision
for HEVC Intra encoding”, IEEE ICIP, pp. 1578-1582, Sept. 2013.
[12] P. Mehta, “Complexity reduction for intra mode selection in HEVC using OpenMP”, course
website: http://www-ee.uta.edu/Dip/Courses/EE5359/ Section: previous projects, Sub section:
Projects (Spring 2014).
[13] S. Vasudevan, “Fast intra prediction and fast residual quadtree encoding implementation in
HEVC”, course website: http://www-ee.uta.edu/Dip/Courses/EE5359/ Section: previous projects,
Sub section: Projects (Spring 2014).
[14] K.R.Rao , D. N. Kim and J.J. Hwang ,” Video coding standards: AVS China, H.264/MPEG4 Part10, HEVC, VP6, DIRAC and VC-1"´, Springer, 2014.
[15] G.Sullivan et al, “Standardized Extensions of the High Efficiency Video Coding (HEVC)
Standard”, IEEE Journal of Special Topics in Signal Processing, vol.7, No. 6, pp. 1001-1016,
Dec 2013.
[16] Test Sequences: ftp://ftp.kw.bbc.co.uk/hevc/hm-11.0-anchors/testsequences/
[17] F. Bossen et al, "HM Software Manual", JCT-VC of ITU-T SG16 WP3 and ISO/IEC
JTC1/SC29/WG11, AHG chairs, January 2014.
[18] B. Bross et al, “High Efficiency Video Coding (HEVC) Text Specification Draft 10”,
Document JCTVC- L1003, ITU-T/ISO/IEC Joint Collaborative Team on Video Coding (JCTVC), Mar. 2013 available on
http://phenix.it-sudparis.eu/jct/doc_end_user/current_document.php?id=7243
[19] JVT Draft ITU-T recommendation and final draft international standard of joint video
specification (ITU-T Rec. H.264-ISO/IEC 14496-10 AVC), March 2003, JVT-G050 available on
http://ip.hhi.de/imagecom_G1/assets/pdfs/JVT-G050.pdf
[20] I.E.G. Richardson, “The H.264 advanced video compression standard”, 2nd Edition,
Hoboken, NJ, Wiley, 2010.
[21] Intra Prediction Modes of H.264 https://www.google.com/search?q=intra+prediction+modes+h.264