New pixel-DCT domain coding technique for object based and frame based prediction error [video coding]

The discrete cosine transform (DCT) is widely used in modern video compression standards, such as the ITU-T H.263 and the ISO MPEG-4, to achieve high compression efficiency. A major merit of the DCT is its capability in high energy compaction for natural images. However, the motion prediction error frame is not a natural image but synthetically generated by the process of motion compensation. This process degrades the energy compaction efficiency of the DCT. We study the spatial distribution of the prediction errors resulting from either the full-search motion estimation or other fast search algorithms in order to improve the coding efficiency of the DCT. Subsequently, a mixed spatial-DCT-based coding scheme is proposed for coding the prediction errors. Our experimental results show that this coding scheme can successfully improve the compression performance of the traditional DCT-based video coder with block based motion compensation for arbitrary shaped video objects and, video sequences which contain moderate to high motion activities.