Lossless Compression of Dithered Images With the Pseudo-distance Technique

Despite many advances, still image storage and transfer, particularly in low-cost devices, remain to be important problems. For example, some wireless phone displays do not have the capacity to handle true colors. To remedy this problem, a color quantization (color palette) technique is often applied to images in order to reduce the number of colors. However, to avoid the side effects of the color-quantization, usually a process called dithering is applied to quantized images. Dithering techniques approximate colors which are not available in the palette by utilizing a diffusion technique of colored pixels from within the available palette. In this work, we examine compression of color-quantized images with different dithering techniques and show that the recently introduced modified pseudo-distance technique yields better compression results than the well-known GIF and PNG techniques.