An Efficient Intermode Decision Algorithm Based on Motion Homogeneity for H.264/AVC

The latest video coding standard H.264/AVC significantly outperforms previous standards in terms of coding efficiency. H.264/AVC adopts variable block sizes ranging from 4 $\times$ 4 to 16 $\times$ 16 in inter frame coding, and achieves significant gain in coding efficiency compared to coding a macroblock (MB) using regular block size. However, this new feature causes extremely high computation complexity when rate-distortion optimization (RDO) is performed using the scheme of full mode decision. This paper presents an efficient intermode decision algorithm based on motion homogeneity evaluated on a normalized motion vector (MV) field, which is generated using MVs from motion estimation on the block size of 4 $\times$ 4. Three directional motion homogeneity measures derived from the normalized MV field are exploited to determine a subset of candidate intermodes for each MB, and unnecessary RDO calculations on other intermodes can be skipped. Experimental results demonstrate that our algorithm can reduce the entire encoding time about 40% on average, without any noticeable loss of coding efficiency.