Advanaced video coding for reducing complexity in h 264 2

This is due to the fact that a number of new techniques are adopted, which include directional prediction for intra coded blocks, variable block size for inter coded blocks, multi-refere

ACKNOWLEDGEMENTS

Without help of many people and parties, the thesis would not have been completed by this moment First of all, I would like to express my heartfelt gratitude to my supervisor, Dr Ko Chi Chung, for his valuable advice and guidance during various phases of my study, especially for his serious research attitude and his encouragement

on me to take the challenges Secondly, I need to give thanks to NUS for providing

me with an opportunity of pursuing further research and study in such a beautiful university I miss all those lecturers and classmates with whom I spent great time together Thirdly, I would like to thank Institute for Infocomm Research for giving good support during the entire process of my research Without this support, the timely completion of the thesis is unimaginable Last but not least, I strongly appreciate my family for their deep understanding Thanks to my wife, for her love, patience and encouragement throughout my Ph.D study period Thanks to my lovely daughter Her birth has brought me a new chapter of my life and new angle of view to look at this world Thanks to my parents, for taking good care of my daughter, and their confidence in my capability, determination and passion to excel all the time

TABLE OF CONTENTS

ACKNOWLEDGEMENTS i

TABLE OF CONTENTS ii

SUMMARY vi

NOMENCLATURE viii

LIST OF FIGURES x

LIST OF TABLES xii

CHAPTER 1 INTRODUCTION 1

1.1 Background 1

1.2 Objectives 2

1.3 Thesis Contributions 3

1.4 Organization of the Thesis 4 CHAPTER 2 H.264 AND LITERATURE SURVEY 6

2.1 H.264 6 2.2 H.264 Encoder 9

2.3 H.264 Decoder 10

2.4 Predictive Coding 11

2.4.1 Intra Coding 11

2.4.2 Inter Coding 14

2.5 Motion Estimation 15

2.6 Mode Decision 17

2.7 Literature 18

CHAPTER 3 FAST INTRA MODE DECISION FOR H.264 29

3.1 Overview of Intra Coding in H.264 30 3.2 Determining the Primary Edge Direction in the Image Block 32

3.2.2.1 4 x 4 luma block edge direction histogram 35 3.2.2.2 Edge direction histogram for 16 x 16 luma and 8 x 8 chroma

3.3 Mode Decision for Intra Prediction 38 3.3.1 4 x 4 Luma Block Prediction Modes 40 3.3.2 16 x 16 Luma Block Prediction Modes 40 3.3.3 8 x 8 Chroma Prediction Mode 41 3.3.4 Algorithm Complexity Analysis 41

3.4.1 Experiments on IPPPP Sequences 43 3.4.2 Experiments on All Intra Frames Sequences 46 3.4.3 Experiments on IBBPBB Sequences 48 3.4.4 Comparison of Different Fast Intra Prediction Methods 51

4.1.1 Inter Mode Decision in H.264/AVC 53

4.1.2 Observations and Motivation 55 4.2 Determination of Homogenity and Stationarity 57 4.2.1 Homogeneous Regions Determination 57 4.2.2 Stationary Regions Detection 59

4.3.1 Experiments on IPPP Sequences 63 4.3.2 Experiments on IBBP Sequences 64

CHAPTER 5 FAST INTRA 4X4 MODE ELIMINATION APPROACHES FOR

H.264 69

5.2 Fast Intra 4 x 4 Mode Elimination 72

CHAPTER 6 ADAPTIVE INTERPOLATION APPROACHES FOR H.264

79

6.3 General Interpolation Approaches 82

6.4.1 Approach One 84

7.2.2 Reordering Motion Estimation Steps for Different Block Sizes 96

REFERENCE 97

SUMMARY

The new international video coding standard H.264, also known as Advanced Video Coding (AVC), has been proposed by JVT Compared to previous video coding standards, H.264/AVC has significantly better performance in terms of being able to achieve much better peak signal-to-noise ratio (PSNR) and visual quality at the same bit rate This is due to the fact that a number of new techniques are adopted, which include directional prediction for intra coded blocks, variable block size for inter coded blocks, multi-reference frame motion estimation, integer transform, in-loop filter and context-based adaptive binary arithmetic coding (CABAC), and rate distortion optimization (RDO) Unfortunately, this good performance is obtained at the expense

of very high computational complexity Therefore, the main aim of this thesis is to develop fast algorithms that can improve the encoding speed of H.264 without significant loss of visual quality

A fast mode decision algorithm is firstly presented for intra prediction in H.264 video coding By making use of the edge direction histogram, the number of mode combinations for luma and chroma blocks in a macroblock (MB) that take part in the rate distortion optimization calculation has been reduced significantly from 592 to as low as 132 This results in great reduction in the complexity and computation load of the encoder Experimental results show that the fast algorithm has negligible loss of PSNR compared to the original H.264 scheme

Secondly, a fast inter mode decision algorithm is proposed to decide the best mode in the inter coding of H.264 It makes use of the spatial homogeneity and the temporal stationarity characteristics of the textures of video objects Specifically,

homogeneity decision of a block is based on edge information inside the block, and co-sited MB difference is used to decide whether the MB is temporal stationary Based on the homogeneity and stationarity of video objects, only a small number of inter modes are used in RDO The experimental results show that the fast algorithm is able to reduce much encoding time, with negligible PSNR loss

Thirdly, two fast intra 4x4 mode elimination methods are proposed for H.264 coding The lossless method checks the cost after each 4x4 block intra mode decision, and terminates if the cost is higher than the minimum cost of inter mode coding On the other hand, by using some low cost preprocessing to make prediction, the lossy method terminates if the cost is higher than some fraction of this minimum cost Experimental results show that the lossless method can reduce the encoding time without any sacrifice of visual quality The lossy method can further reduce encoding time with negligible PSNR loss or bit rate increase

Finally, this thesis presents two adaptive interpolation methods that can significantly reduce the interpolation operation in H.264 coding By making use of the flag matrix data structure and using interpolation on-demand, the proposed methods are able to increase the encoder speed greatly without any PSNR loss or increase in bit rate

NOMENCLATURE

CABAC context-based binary arithmetic coding

CAVLC context-based variable length coding

CIF common interchange format

DC direct coefficient

ISO International Standard Organization

ITU International Telecommunication Union

MPEG Motion Picture Experts Group

MV motion vector

QP quantization parameter

SAD Sum of Absolute Difference

ME/MC motion estimation/motion compensation

MV motion vector

FIR Finite Impulse Response

LIST OF FIGURES

Figure 2.1 H.264 encoder architecture

Figure 2.2 H.264 decoder architecture

Figure 2.3 Intra 4x4 prediction modes

Figure 2.4 Intra 16x16 prediction modes

Figure 2.5 Variable partition sizes employed in inter coding

Figure 2.6 Multi-frame motion estimation/motion compensation

Figure 3.1 An example of intra prediction

Figure3.2 Examples of 4x4 edge patterns and their preferred intra predication

directions

Figure 3.3 Edge direction histogram of 4 x 4 blocks

Figure 3.4 Intra 8 x 8 and 16 x 16 prediction mode directions

Figure 3.5 Edge direction histogram of 16 x 16 luma and 8 x 8 chroma blocks

Figure 3.6 News, Ch_Psnr = -0.067dB, Ch_Bits =1.226 %

Figure 3.7 Mobile, Ch_Psnr = -0.018dB, Ch_Bits =0.451%

Figure 3.8 Time saving at different intra periods

Figure 3.9 Time saving at different size of searching area

Figure 3.10 News, Ch_Psnr = -0.294dB, Ch_Bits =3.902%

Figure 3.11 Mobile, Ch_Psnr = -0.255dB, Ch_Bits =3.168%

Figure 3.12 News, Ch_Psnr = -0.156dB, Ch_Bits =3.106%

Figure 3.13 Mobile, Ch_Psnr = -0.013dB, Ch_Bits =0.379%

Figure 4.1 Different partitions in an MB

Figure 4.2 Segmentation of video objects in H.264 algorithm

Figure 4.3 RD curve for ‘News’ (IPPP)

Figure 4.4 RD curve for ‘Mobile’ (IPPP)

Figure 4.5 RD curve for ‘News’ (IBBP)

Figure 4.6 RD curve for ‘Mobile’ (IBBP)

Figure 5.1 Overall mode decision process

Figure 5.2 Border difference of 4 x 4 block

Figure 6.1 Half pixel interpolation

Figure 6.2 Quarter pixel interpolation

Figure 6.3 Match between current block and reference block

Figure 6.4 Active and Inactive macroblocks

Figure 6.5 Reference blocks in the reference frame

Figure 6.6 Interpolated frame memory reorganization

Figure 6.7 Flag matrix for a Quarter CIF frame

Figure 6.8 Flow chart of the second approach

LIST OF TABLES

Table 3.1 Number of candidate modes

Table 3.2 Results for IPPPP sequences

Table 3.3 Results for IIIII sequences

Table 3.4 Results for IBBPB sequences

Table 3.5 Comparison of different fast intra prediction methods

Table 4.1 Results for IPPP sequences

Table 4.2 Results for IBBP sequences

Table 4.3 Results for ‘News’ (IPPP)

Table 4.4 Results for ‘Mobile’ (IPPP)

Table 4.5 Results for ‘News’ (IBBP)

Table 4.6 Results for ‘Mobile’ (IBBP)

Table 5.1 Codec Performance (QP=28)

Table 5.2 Codec Performance (QP=32)

Table 5.3 Codec Performance (QP=36)

Table 5.4 Codec Performance (QP=40)

Table 6.1 Speed increase at QP = 16

Table 6.2 Speed increase at QP = 32