Bi-directional object-based coding in video compression at very low bitrate
An algorithmic architecture of video compression at a very low bitrate is presented. This architecture incorporates block-based as well as object-based coding algorithms and manages them in a cooperative way in which different algorithms are applied to different image frames iteratively: I and P frames are coded by a block-based algorithm and B frames are coded by a bi-directional object-based algorithm. An extra degree of freedom in video coding is introduced in order to achieve higher compression ratios while maintaining good visual quality. We emphasize the details of the object-based algorithm which is based on the source model of rigid 2D-objects with 3-D motions. Simulations are done for MPEG-4 Class A/B test sequences which contain low to medium spatial detail and a low amount of movement but is not restricted to head and shoulder images. The results are encouraging in that the coder provides a higher image quality with a satisfactory motion effect.