Feedback loop for coder control in a block-based hybrid coder with mesh-based motion compensation

摘要

In this paper, the motion estimation and motion compensation within a block-based hybrid coder is modified. Input to the motion estimator is the original frame and a representation of the previously decoded frame generated by means of a second prediction loop. The second prediction loop works in parallel to the prediction loop of the decoder. It distinguishes itself from the conventional coder prediction loop such that for blocks with transmitted DCT coefficients, the original image signal is fed into the second prediction loop, and for blocks without transmitted DCT coefficients, the motion compensated signal is fed into the prediction loop. The image generated by the second prediction loop is influenced by motion but not by the quantization noise of the DCT. The motion-compensated prediction image from the second predictor loop can be easily used for control of the encoder. This coder control is not influenced by the actual quantization selected by the encoder and hence very stable for a wide range of bit rates. Savings of 15% to 25% in bit rate can be observed without loss of subjective picture quality.