Fast intra mode decision algorithm based on directional gradients for H.264/AVC
Yan Han · Signal Processing · 2012
A directional gradients operator is proposed in this paper,and a novel H.264 intra prediction was introduced based on this operator.First of all,an encoding 16×16 macro block was divided into sixteen 4×4 sub-block.Using this directional gradients operator,an encoding 4×4 luma sub-block's texture feature and grey level fluctuation can be calculated.Based on these features,some dispensable 4×4 intra prediction modes were cut down.Furthermore,the 16×16 macro block's texture feature and grey level fluctuation can be judged according to statistical information of each 4×4 sub-block's candidate intra prediction modes.And the 16×16 candidate intra prediction modes can be decided by using the threshold of directional gradient strength value.The rate distortion optimization process should be done among the 4×4 and 16×16 candidate intra prediction modes and the best luma intra prediction mode should be decided.In addition,8×8 chroma block intra prediction modes could also be reduced based on the corresponding luma macro block.In all,the number of intra prediction mode was reduced up to 50%,and the computational complexity was highly reduced.According to experiments,the proposed method could reduce the encoding time of overall sequence by about 50% without noticeable degradation of coding quality.