Visual Progressive Coding

The embedded coder has an attractive feature that the coding bitstream can be truncated later at any point and still decoded a perceptible image. It is common in conventional coding to improve the subjective quality of the coded image through adjusting the quantization step size inversely proportional to a set of visual weights. However, such scheme will not be effective in the embedded coder as different viewing condition may be called for at different stages of embedding. In this paper, we propose the visual progressive coding (VIP), which uses the visual weights to determine the order of embedding, rather than to requantize the transform coefficients. VIP can change the weights halfway through redefining the order of embedding according to the active weights. With such “reordering by weight” strategy, it is feasible to adjust the visual weights flexibly during the embedding process, and improve the subjective appearance of the image over the entire bit rate.