Hybrid block-based/segment-based video compression at very low bit rate
An algorithmic architecture of video compression at very low bit rate is presented. This architecture incorporates block-based as well as segment-based coding algorithms and manages them in a cooperative way in which different approaches are applied to different image frames iteratively: I and P frames are coded by block-based algorithm and O frames are coded by segment-based algorithm. An extra degree of freedom in video coding is introduced in order to achieve higher compression ratios while maintaining good visual quality. Every other frame in the image sequence is coded using block-based coding (ITU-T H.263) with motion (block-matching, 2D translations) and color (DCT) coefficients. These I and P frames are allocated with more bits, generating images with higher spatial accuracy, and providing the coder with generic coding capability. Between every two P frames, the O frame is coded using segment-based algorithm providing the motion (rigid 2D source models, 3D motions) and shape (polygon or spline approximation) information. Since only motion prediction is provided, pixel values are copied or interpolated from neighboring P frames. With good segmentation and affine transform, the prediction can preserve the natural shapes of the objects and give natural motion information which is sufficient for very low bitrate coding. These frames are allocated with less bits, generating images with less temporal accuracy, but providing the coder with higher compression efficiency.