The USC Andrew and Erna Viterbi School of Engineering USC Signal and Image Processing Institute USC Ming Hsieh Department of Electrical and Computer Engineering University of Southern California

Technical Report USC-SIPI-405

“Advanced Techniques for High Fidelity Video Coding”

by Qi Zhang

August 2010

This research focuses on two advanced techniques for high-bit-rate video coding: 1) subpel motion estimation and 2) residual processing.

First, we study sup-pixel motion estimation for video coding. We analyze the characteristics of the sub-pel motion estimation error surface and propose an optimal subpel motion vector resolution estimation scheme that allows each block with different characteristics to maximize its RD gain through a flexible motion vector resolution. Furthermore, a direct subpel MV prediction scheme is proposed to estimate the optimal subpel position. The rate-distortion performance of the proposed motion prediction scheme is close to that of full search while it demands only about of 10% of the computational complexity of the full search.Secondly, we investigate high-bit-rate video coding techniques for high definition video contents. We observed that under the requirements of high-bit-rate coding, there still left a large portion of uncompensated information in the prediction residual that represents similar signal characteristics of _lm grain noise. Due to small quantization step size used by high-bit-rate coding, these untreated small features render all existing coding schemes ineffective. To address this issue, a novel granular noise prediction and coding scheme is proposed to provide a separate treatment for these residuals. A frequency domain- based prediction and coding scheme is proposed to enhance the coding performance. The proposed granular noise prediction and coding scheme outperforms H.264/AVC by an average of 10% bit rate saving.

Thirdly, we further investigate on the impact of high-bit-rate coding from the more fundamental signal characteristics point of view. A probability distribution analysis on DCT coefficients from the H.264/AVC codec under different bit rates is conducted to reveal that the prediction residual in the form of DCT coefficients have a near uniform distribution for all scanning positions. To further understand this phenomenon, a correlation based analysis was conducted to show that the different types of correlations existed in the video frame and the distribution of these correlations highly impact the coding efficiency. A significant amount of short and medium-range correlations due to the use of a fine quantization parameter cannot be easily removed by existing compensation techniques. Consequently, the video coding performance degrades rapidly as quality increases. A novel Multi-Order-Residual (MOR) coding scheme was proposed. The concept is based on the numerical analysis to extract different correlation through different phases. A different DCT-based compensation and coding scheme combined with an improved rate-distortion optimization process was proposed to target the higher-order signal characteristics. An additional pre-search coefficient optimization phase was proposed to further enhance compression performance. Experimental results show that the proposed MOR scheme outperforms H.264/AVC by an average of 16% bit rate savings.

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