Research of Color image coding using image-adaptive quantization

Using JPEG standard, Color still images can be compressed in high ratios while good quality can be guaranteed. The framework of the JPEG is specified, but the recommended quantization table and the Huffman table can be pruned according to the image's characteristic. In this paper, we put forward an adaptive-quantization approach which is compatible for the baseline JPEG. In our approach, we statistically calculate the image's average probability distributivity, which used as the threshold for the quantization. The quanti-table recommended by JPEG can then be justified with the characteristic of images and the average code-rate is noticeably dropped.