Horizontal Spatial Prediction for High Dimension Intra Coding*

Pin Tao, Wenting Wu, Chao Wang, Mou Xiao, Jiangtao Wen Dept. of Computer Science and Technology, Tsinghua University, Beijing 100084

Key Laboratory of Pervasive Computing, Ministry of Education, China taopin@tsinghua.edu.cn, {wuwt08, bottlehalf, xiaomou, jiangtao.wen}@gmail.com

Macroblock level Horizontal Spatial Prediction(HSP) based intra frame coding scheme for High Dimension(HD) video sequences was proposed in this paper. According to the correlation experiment on HD sequences, most HD pictures have the stronger horizontal spatial correlation than the vertical spatial correlation, about 2dB stronger. This phenomena drop a valuable hint to us that the horizontal spatial prediction can be used in HD video intra coding without considering the vertical spatial prediction. An adaptive divide and predict intra frame coding scheme has been proposed by Piao[1] which has the similar idea. But this method divided the whole picture into several parts which is not conform to the conventional macroblock based video coding framework and it has the high computation complexity in motion estimation procedure.

We proposed to divide the pixels of a 16x16 macroblock into the odd pixels and even pixels in horizontal. The right 8x16 block, even pixels, will be encoded and reconstructed with the conventional way. Then the reconstructed pixels are used to predict the left 8x16 blcok, odd pixels, with 6-tap interpolation filter. Both of the even and odd parts are combined together to calculate the rate-distortion cost. This is the HSP-I16x16 mode. For some complicate texture macroblocks which are encoded as I4x4 in conventional H.264 method, both of the right and left 8x16 blocks will also be divided into several 4x4 sub-blocks. In every 8x8 block group, four 4x4 sub blocks are encoding from the left-up, right-up to left-bottom and right-bottom. The block groups are also processing under the similar order. With this order, left bottom block group can benefit from the reconstructed pixels in right-up block group. This is the HSP-I4x4 mode. Finally, the proposal HSP method will compete with the conventional H.264 intra prediction method based on rate-distortion optimization. More HSP mode are chosen, more improvement will be seen on the whole intra frame. The additional cost of HSB based intra coding comes from an additional bit will be needed for each macroblcok to indicate the decoder side whether it is HSP mode or not. According to our experiment, these additional bits take about 1% of the total intra frame.

The first 10 frames of HD sequences(including BigShips, City, Crew, Night, ShuttleStart) with 1280x720 picture size are coded with the proposed HSP method as intra frames. QP is select from 28, 31, 34, 37, fame-rate is 30fps, and I8x8 is disabled while I4x4 and I16x16 are enabled. The algorithm is implemented on the H.264 reference software JM15.1[2]. Comparing with the conventional H.264 intra coding scheme, experiment results show that HSP method can improve the performance with about 0.17dB and reduce the bit-rate by about 3.1%. With the statistic in the encoder, about 30%-60% macroblocks can be benefit from the proposal HSP method. References [1] H.W.Park, Y. P., "An Adaptive Divide-and-Predict Coding for Intra-Frame of H.264/AVC." ICIP 2009. [2] H.264/AVC JM reference Software: http://iphome.hhi.de/suehring/tml/download/.

* The work is supported by National High-Tech Research and Development Plan of China 2007AA11Z223, 2009AA011901 and 2009AA012103, Natural Science Found Research Project 60833009 and 60773158

2010 Data Compression Conference

1068-0314/10 $26.00 © 2010 IEEE

DOI 10.1109/DCC.2010.76

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