Intra prediction coding is one of the many coding-efficiency oriented tools of H.264/AVC, but it requires high computational complexity. Many fast intra coding algorithms have been proposed to reduce the computational complexity of intra prediction, but most of them have been focused on the mode decision methods themselves. In this paper, we propose a fast algorithm in which new intra modes are substituted for certain of the conventional intra modes, so that the number of intra modes can be reduced. The proposed intra modes, namely the weighted mean and median modes, can effectively represent the directions of a block in a frame. The simulation results showed that the proposed method could reduce the encoding time of the overall sequence by about 11 % and that of the I-frames by about 28%, without any noticeable degradation of the coding efficiency
Intra prediction in H.264/AVC uses 9 modes in 4×4 luma block, 4 in 16×16 luma and 8×8 chroma blocks. Intra prediction modes utilize similarity of current macroblock with pre-encoded neighboring macroblocks and directionality of image in pixel domain. Therefore its coding efficiency in H.264/AVC is improved compared to the conventional video codecs such as MPEG-2 and MPEG-4. However coding efficiency in intra-coded frame is much lower compared to that of inter slice since the intra prediction modes use only limited neighboring macro blocks and then to obtain good matched reference block image using intra prediction may be more difficult than inter prediction. Therefore for higher coding efficiency, it is very important to get good matched prediction block in a given envirionment. In general video codec which uses general 4:2:0 YCbCr format, overall coding efficiency issue is mainly focused on luma relative to chroma components. In this paper, we propose additional intra luma prediction mode using collocated chroma pixels and weight values. The proposed method utilizes collocated chroma macroblocks as reference image for more efficient intra luma prediction.