EE 5359PROJECT REPORTTopic: Complexity Reduction Algorithm for IntraMode selection in H.264/AVC Video CodingBy Amruta KulkarniStudent ID: 1000666836 Under the guidance of Dr. K. R. RaoTABLE OF ACRONYMSAVC advanced video codingCABAC context adaptive binary arithmetic codingDCT discrete cosine transform I-frame intra frameJM joint modelMSE mean square errorPSNR peak signal to noise ratioSSIM structural similarity index metricVLC variable length codingRDO rate distortion optimizationMPEG moving picture experts group VCEG video coding experts group FMO flexible macro block orderingASO arbitrary slice orderingRS redundant slicesSATD sum of absolute transformed differencesImplementation of Complexity reduction algorithm for intramode selection in H.264/AVC Video CodingObjective: It is proposed to implement a complexity reduction algorithm for intra modeselection in H.264/AVC video coding [5]. Need for the same arises as, the mode decisionalgorithm used for H.264 encoding is inherently complex. The encoding time required fora single macro block depends on the number of computations. The mode decision processcan be made simpler by reducing the number of computations; this algorithm proposes todo the same. Introduction: H.264 is an Advanced Video Compression standard, developed by ITU-T VideoCoding Experts Group together with ISO/IEC Moving Picture Experts Group [1]. It isthe widely used video codec in mobile applications, internet (YouTube, flash players),set top box, TV etc. A H.264 encoder converts the video into a compressed format(H.264) and a decoder convert’s compressed video back into an uncompressedformat. A H.264 video encoder carries out prediction, transform and encodingprocesses to produce a compressed H.264 bit stream. The H.264 encoder blockdiagram is shown in Fig.1. [1]Fig. 1 H.264 encoder block diagram [1]A decoder carries out a complementary process by decoding, inverse transform andreconstruction to output a decoded video sequence. Fig. 2 shows the basic buildingblocks of H.264 decoder.Fig. 2 H.264 decoder block diagram [1]The H.264 encoder forms a prediction of the current macro block – One based on thecurrent frame using intra prediction/spatial prediction technique. Intra prediction is animportant technique in image and video compression to exploit spatial correlationwithin one picture. Intra prediction supports the following block sizes. [8]a) 16x16 (for Luma) – H.264 Intra 16x16 prediction modes are shown in Fig. 2a Mode 0 (vertical): extrapolation from upper samples (H). Mode 1 (horizontal): extrapolation from left samples (V). Mode 2 (DC): mean of upper and left-hand samples (H+V). Mode 3 (Plane): a linear “plane” function is fitted to the upper and left-handsamples H and V. This works well in areas of smoothly-varying luminance.Fig.2a 16x16 intra prediction modes [9]b) 8x8 (for Chroma) – Mode 0 (DC): mean of upper and left-hand samples (H+V). Mode 1 (horizontal): extrapolation from left samples (V). Mode 2 vertical): extrapolation from upper samples (H). Mode 3 (Plane): a linear “plane” function is fitted to the upper and left-handsamples H and V. This works well in areas of smoothly-varying luminance.b) 4x4 (for Luma) –H.264 Intra 4x4 prediction modes are shown in Fig.2b. The intra 4x4 prediction has 9directional modes as listed below. Mode 0 - Vertical Mode 1 - Horizontal Mode 2 - DC Mode 3 - Diagonal-down-left Mode 4 - Diagonal-down-right Mode 5 - Vertical-Right Mode 6 - Horizontal-down Mode 7 - Vertical-left Mode 8 - Horizontal-upFig. 2b Intra prediction 4x4 modes [2]A-H -> they are previously coded pixels of the upper macro block and are available bothat encoder/decoder.I-L -> they are previously coded pixels of the left macro block and are available both atencoder/decoder.M -> this is previously coded pixel of the upper left macro block.Inter Prediction in H.264- [2]Inter prediction is the process of predicting a block of luma and chroma samples froma picture that has previously been coded and transmitted, a reference picture. Thisinvolves selecting a prediction region, generating a prediction block and subtractingthis from the original block of samples to form a residual that is then transformed,coded and transmitted. The block size can range from 16x16 to 4x4 luma andcorresponding chroma samples as shown in Fig. 4 and Fig.5. Fig. 4 Macro block partitions: 8x8, 4x8, 8x4, 4x4 [9]Fig. 5 Macro block sub partitions: 8x8, 4x8, 8x4, 4x4 [9]Rate Distortion Optimization [6]-The H.264/AVC intra-prediction is conducted for all types of blocks such as 4x4 lumablocks, 16x16 luma blocks, and 8x8 chroma blocks. The residual between the currentblock and its prediction is then transformed, quantized, and entropy coded.To obtain the best mode among these modes, the H.264/AVC encoder performs therate-distortion optimization (RDO) technique for each macro block. Set macro block parameters : QP (quantization parameter) and Lagrangianmultiplier λMODE Calculate : λMODE = 0.85x 2(QP-12)/3 Then calculate cost, which determines the best mode Cost = D + λ MODE x R, D – Distortion R - Bit rate with given QPDistortion (D) is obtained by SSD (sum of squared differences) between the originalmacro block and its reconstructed block. Bit rate(R) includes the number of bits for the mode information and transformscoefficients for macro block.Considering the RDO procedure for intra mode selection in H.264/AVC, the numberof mode combinations in one macro block is N8x (16xN4 + N16) N8 – number of modes of an 8x8 chroma block N4 – number of modes of an 4x4 luma block N16 – number of modes of an 16x16 luma block Computing best mode for one macro block: N8x (16xN4 + N16) = 4 x (16 x 9 + 4) = 592 Thus, to select the best mode for one Macro block in the intra prediction, theH.264/AVC encoder carries out 592 RDO calculations. As a result, the complexity ofthe encoder increases extremely.Goal: This project uses the baseline profile, as it provides simplicity inimplementation. The profiles supported by H.264/AVC are shown in Fig.6:- Baseline profile- Main profile - High profile- Extended profileFig. 6 the specific coding parts of the profiles in H.264 [10]The important
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