FAST MODE DECISION ALGORITHM FOR INTRA PREDICTION IN HEVC Lanka Naga Venkata Sai Surya Teja Student ID Mail ID Date 03/02/2014 UNDER THE GUIDANCE OF Dr. K. R. Rao

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 when compared with the default method of intra prediction in HM Also analysis of PSNR, BD- PSNR, SSIM, BD- Bitrate can be done by comparing with the default encoding scheme in HM 13.0 [5].

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). 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.

BLOCK DIAGRAM OF HEVC ENCODER[15]

BLOCK DIAGRAM OF H.264 ENCODER[20]

BLOCK DIAGRAM OF HEVC DECODER[15]

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 rate-distortion optimization process To reduce the computational complexity of the encoder, a fast intra mode decision [4] was adopted in HM13.0 [5]

CODING TREE ALGORITHM

(c)(d)

OVERVIEW OF INTRA PREDICTION 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

HEVC INTRA PREDICTION MODES [7]

H.264 INTRA PREDICTION MODES[21]

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]

Combining the three steps, fast mode decision algorithm can be performed in intra prediction The unified intra in HM1.0 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 HM13.0 Therefore, there is still some space for further reducing the encoder complexity

TEST SEQUENCES [1] BQSquare_416x240_60

[2] BQMall_ 832x480_60

[3] KristenAndSara_1280x720_60

ACRONYMS BD- Bitrate - Bjøntegaard Delta Bitrate BD- PSNR - Bjøntegaard Delta Peak Signal-to-Noise Ratio CU- 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

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 – 1668, Dec [2] JCT-VC, “WD1: Working Draft 1 of High-Efficiency Video Coding”, JCTVC-C403, JCT-VC Meeting, Guangzhou, October [3] Coding tree structure - [4] Y. Piao et al, “Encoder improvement of unified intra prediction,” JCTVC-C207, Guangzhou, October [5] Software for HEVC - [6] T.L. Silva et al, ”HEVC intra coding acceleration based on tree inter-level mode correlation”, SPA 2013 Sep.2013, Poznan, Poland [7] H. Zhang and Z. Ma, ”Fast intra prediction for high efficiency video coding ”, Pacific Rim Conf. on Multimedia, PCM2012, Singapore, Dec [8] M. Zhang et al, ”An adaptive fast intra mode decision in HEVC ”, IEEE ICIP 2012, pp , Orlando, FL, Sept.- Oct

[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 , Apr [10 ]A. Saxena and F. Fernanades, “Mode dependent DCT/DST for intra prediction in block based image/video coding”, IEEE ICIP, pp , Sept [11] M. Khan et al, “An adaptive complexity reduction scheme with fast prediction unit decision for HEVC Intra encoding”, IEEE ICIP, pp , Sept [12] P. Mehta, “Complexity reduction for intra mode selection in HEVC using OpenMP”, course website: Section: previous projects, Sub section: Projects (Spring 2014). [13] S. Vasudevan, “Fast intra prediction and fast residual quadtree encoding implementation in HEVC”, course website: 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/MPEG-4 Part10, HEVC, VP6, DIRAC and VC-1"´, Springer, 2014.

[15] G.Sullivan et al, “Standard Extensions of the High Efficiency Video Coding (HEVC) Standard” Journal of Special Topics in Signal Processing, vol.7, No. 6, pp , Dec [16] Test Sequences: ftp://ftp.kw.bbc.co.uk/hevc/hm-11.0-anchors/testsequences/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 (JCT-VC), Mar available on sudparis.eu/jct/doc_end_user/current_document.php?id=7243http://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 AVC), March 2003, JVT-G050 available on G050.pdf

[20] I.E.G. Richardson, “The H.264 advanced video compression standard”, 2nd Edition, Hoboken, NJ, Wiley, [21] Intra Prediction Modes of H