Block-based histogram packing of color-quantized images

Reordering the color table of color-quantized images is a very effective approach towards the improvement of the compression efficiency of color-indexed images. In this paper, we provide experimental results showing that, for images generated by color-quantization of full color natural images, histogram packing applied on a block basis is able to provide additional compression improvements of around 15%. In other words, we show that the improvements provided by a global color table reordering can be further increased by applying a local preprocessing technique which packs the histograms of regions (blocks) of the index image.