Adaptive intra modes reduction by clustering for H.264/AVC

H.264/AVC adopts intra coding technique to reduce spatial redundancies. In order to achieve better coding performance, there are nine candidate modes for 4×4 block unit to be selected by Rate-Distortion Optimization(RDO) process in the H.264/AVC encoder-side. However, too many intra candidate modes undoubtedly increase the transmitted bits that represent them. To solve this problem, a novel method for reducing the number of intra modes is proposed in this paper. For each 4×4 block, our algorithm can cluster the nine candidate modes into several groups and selects one mode from each group as a representative of all the modes in this group, so the cost of transmission can be reduced significantly because of the reduction of number of candidate modes. Experimental results show that the proposed method achieves 3.2% bit-rate reduction on average for various video sequences. The improvement of coding performance can be up to 7% bit-rate reduction at low bit rate, averagely.