Block-sorting transformations with pseudo-distance technique for lossless compression of color-mapped images

Color-mapped images are widely used in many applications, especially in WWW, and are usually compressed with Graphic Interchange Format (GIF) without any loss. In our recent work, we showed that further compression gains can be achieved for color-mapped images over GIF when a structured arithmetic coder is used along with the pseudo-distance metric, instead of a Huffman coder as suggested by others. In this work, we show that further compression gains are possible when block-sorting transformations are employed along with the pseudo-distance technique.