Selection of image encoding mode based on preliminary prediction-based encoding stage

摘要

A method for encoding blocks of image pixels, which may form an ultra-high definition image 101, comprises: providing a preliminary prediction-based encoding 106 of original blocks, comprising obtaining a preliminary prediction residual image portion resulting from the difference between the original blocks and corresponding predictors; segmenting the preliminary prediction residual image portion into preliminary prediction residuals; and providing a second prediction-based encoding of original blocks. The second prediction-based encoding involves choosing a coding mode to apply to each prediction residual, from among several coding modes including a static coding mode 111 and a probabilistic coding mode 112A. The static coding mode implements quantization using only predefined quantizers, which may be user-defined, and the probabilistic coding mode implements quantization using quantizers selected based on statistics 117 on the preliminary prediction residuals. Selection of the optimal coding mode may be based on encoding costs or rate-distortion criteria. Obtaining the statistics may involve a probabilistic model such as a generalised Gaussian distribution. Identities of the coding modes used may be stored in a quad-tree in the bit stream. A corresponding decoding method is also disclosed.