[30] Dong J., Lou j. and Yu L. (2003), Improved entropy coding method, Doc. AVS Working Group (M1214), Beijing, Chaina. CHAPTER 4

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1 [30] Dong J., Lou j. and Yu L. (3), Improved entropy coding method, Doc. AVS Working Group (M1214), Beijing, Chaina. CHAPTER 4 Algorithm for Implementation of nine Intra Prediction Modes in MATLAB and Simulation results 4.1 Introduction In recent years MATLAB has successfully bridged the gap between the system developer and researcher. With both, system developer and researcher, working on the same platform, the required time for translating a research paper or technical specification into the functional specifications can be significantly reduced. In the preset work to test the functionality of each module of H.264 Encoder, the modules have been coded and tested in MATLAB before taking up the Verilog realization. The previous chapter explained the theoretical approach involved in the implementation procedure of H.264 CODEC. This chapter presents the algorithm for implementation of nine intra prediction modes in MATLAB and also simulation results are discussed at the end of this chapter. 4.2 Algorithm for implementation of nine intra prediction modes in MATLAB In the present work, all the nine modes of intra prediction have been incorporated in the MATLAB implementation for H.264 Encoder, to test the functionality of each module of H.264 Encoder. The modules which have been coded in MATLAB are Transformation, Quantization, Inverse Transformation, Inverse quantization, intra prediction module (integrating all nine modes of intra prediction) and CAVLC. The flowchart of the entire Encoder implementation is presented in Fig The algorithm displays the menu for quantization step, selected by the user as per the requirement. The input image is in TIF format. The algorithm computes and for different values of Quantization steps with and without Intraprediction. The user has the choice of entering desired Quantization step for the computation. Further, it displays the Menu for the selection of Intra prediction, and the mode of Intra prediction. After the Intra prediction mode is selected, the prediction 1

2 matrix P is formed from samples in the current frame that has been previously encoded. Start Input Image in tif Format & Select Qstep Initialize P matrix to zero Start No Choose Mode Yes Mode0 Mode1 Mode8 Select Intra prediction Update P Matrix Compute TQIQIT & Reconstruct image Compute Compute CAVLC for Y, Cb, Cr Estimate Output and achieved Start Figure 4.1: Flowchart of H.264/AVC Encoder Implementation in MATLAB The prediction P is subtracted from the current macro block to produce a 2

3 residual macro block X of 4x4 size. Transformation, Quantization and their inverses are performed on X as described in the previous section. The Prediction matrix P is updated according to the mode of intra-prediction to process the next macro block. is computed for the reconstructed image by computing root mean square error. CAVLC is applied to Y, C b and C r components to estimate the compression in each mode of intra prediction. The execution steps of algorithm is as follows. Step 1: Enter the image in.tif format. Step 2: Choose the Quantization step. Step 3: Convert RGB into Y, Cb &Cr and down sample Cr & Cb into 4:2:0 formats. Step 4: Initialize P matrix to zero. Step 5: Choose any one of the intra prediction Mode out of nine Modes Step 6: Update the P matrix. Step 7: Apply Transformation, Quantization & Inverse Transformation, Inverse Quantization and reconstruct the Image. Step 8: Compute for the reconstructed image Step 9: Compute for Y, Cb, Cr. Step10: Estimate. Step 11: Output the and. Step 12: Stop. 4.3 Simulation Results H.264/AVC Encoder has been implemented in MATLAB for all the nine modes of Intra prediction. The simulations were performed for different image resolutions and for different QP values. For each mode, the reconstructed picture Quality () and were computed. Table 4.1 and 4.2 present the simulated results for QP=16 and QP=8. The following observations may be made from the MATLAB simulated results. 1. In most of the pictures experimented with, compression improves appreciably with Intra prediction than without it up to 54%, and without compromising on the reconstructed quality of the picture. 3

4 2. As QP value increases, the compression also increases. However, high value of QP (beyond 32) degrades the quality of reconstructed picture. A value greater than 30 db is generally acceptable and, a value of 35 db and above implies that the reconstructed picture is indistinguishable from the original. 3. The depends on the picture contents of the original picture. From Table 4.1 and 4.2, we observe that Mode 0, Mode 1 and Mode 8 present greater compression compared to other Modes of Intra prediction for all types of pictures that have been experimented with. 4. All the nine modes of Intra prediction have been implemented. Of these, Vertical Mode (Mode 0), Horizontal Mode (Mode 1) and Horizontal up Mode (Mode 8) offers the highest compression (about 12 to 30), without sacrificing on the quality of the reconstructed picture ( achieved is of about 34 db to 40 db). Table 4.1: Simulation Results of Images: and achieved with Intraprediction for QP=16 Intra prediction Mode Clock, Geneva 1024x768 Blue hills 800 x Lena 512 x 512 QP= Without Intraprediction Table 4.2: Simulation Results of Images: and achieved with Intraprediction for QP=8 Intra prediction Mode Clock, Geneva 1024x768 Blue hills 800 x Lena 512 x 512 QP=

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6 (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Figure 4.2: Simulation Results of H.264 with nine modes of intra prediction for Clock Geneva image (a) Clock Geneva 1024x768 ; Q step =8 Reconstructed Image using MATLAB with (b) Vertical Intra prediction ( db) (c) Horizontal Intra prediction ( db) (d) DC Intra prediction ( db) (e) Diagonal-Down-Left Intra prediction ( db) (f) Diagonal-Down-Right Intra prediction ( db) (g) Vertical-Right Intra prediction ( db) (h) Horizontal-Down Intra prediction ( db) (i) Vertical-Left Intra prediction ( db) (j) Horizontal-Up Intra prediction ( db) 6

7 (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Figure 4.3: Simulation Results of H.264 with nine modes of intra prediction for Blue hills image (a) Blue hills 800 x ; Q step =8 Reconstructed Image using MATLAB with (b) Vertical Intra prediction ( db) (c) Horizontal Intra prediction ( db) (d) DC Intra prediction ( db) (e) Diagonal-Down-Left Intra prediction ( db) (f) Diagonal-Down-Right Intra prediction ( db) (g) Vertical-Right Intra prediction ( db) (h) Horizontal-Down Intra prediction ( db) (i) Vertical-Left Intra prediction ( db) (j) Horizontal-Up Intra prediction ( db) 7

8 (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Figure 4.4: Simulation Results of H.264 with nine modes of intra prediction lena image (a) Lena 512 x 512 ; Q step =8 Reconstructed Lena Image using MATLAB with (b) Vertical Intra prediction ( db) (c) Horizontal Intra prediction ( db) (d) DC Intra prediction ( db) (e) Diagonal-Down-Left Intra prediction ( db) (f) Diagonal-Down-Right Intra prediction ( db) (g) Vertical-Right Intra prediction ( db) (h) Horizontal-Down Intra prediction ( db) (i) Vertical-Left Intra prediction ( db) (j) Horizontal-Up Intra prediction ( 47 db) 8

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11 (9), Context-based entropy coding in AVS Video Coding standard, Signal Procession: Image Communication 24, pp [28] Richardson I. E. G. (2), White Paper H.264/MPEG-4 Part 10: Variable Length Coding. [29] Li Zhang, Xiaolin Wu, Ning Zhang, et.al. (7) Context-based Arithmetic Coding Reexamined for DCT Video, IEEE International Symposium on Circuits and Systems (ISCAS). 11