In this article, we propose an efficient compression algoparameters to fit the very low-bit-rate nature of the applications. rithm for very low-bit-rate video applications. The algorithm is based Despite its good performance, H.263 still suffers from blocking on (a) an optical-flow motion estimation to achieve more accurate effects, an intrinsic problem of the block-matching motion predicmotion prediction fields; (b) discrete cosine transformation (DCT) tion and block DCT implementation. coding of the motion vectors from the optical-flow estimation to re-Many techniques have been proposed to overcome the drawduce the motion overheads; and (c) an adaptive threshold technique backs of the block-matching techniques. One approach is to use to match optical flow motion prediction and minimize the residual overlapped windows [10-12], which was also adopted as an errors. Unlike the classic block-matching based DCT video coding optional feature for H.263. Another approach is to apply variable schemes in MPEG-1/2 and H.261/3, the proposed algorithm uses optical flow for motion compensation and the DCT is applied to the block size (VBS) motion prediction to adapt the motion predicoptical flow field instead of predictive errors. Thresholding techniques tion to the object level. One example of VBS is the locally adapare used to treat different regions to complement optical flow techtive multigrid block-matching motion estimation [9]. There, a nique and to efficiently code residual data. While maintaining a commultigrid structure and a modified three-step search are used. The parable peak signal-to-noise ratio (PSNR) and computational comentropy criterion is established to optimally balance the amount plexity with that of ITU-T H.263/TMN5, the reconstructed video of information corresponding to the prediction error and the repreframes of the proposed coder are free of annoying blocking artifacts, sentation of the motion. Another example uses a quadtree strucand hence visually much more pleasant. The computer simulation are ture and different criteria to remove the constraint of fixed block conducted to show the feasibility and effectiveness of the algorithm. Results at 11 kbps are presented which can be used for videophone size and translational motion to allow more flexibility in the applications in the existing public switched telephone network (PSTN).
motion field .