Lossless Compression of Dithered Images

In order to display high-bit resolution images on low-bit resolution displays, bit resolution needs to be reduced. This problem is vital especially for low-cost or small (mobile) devices. To untangle the bit reduction problem, special color quantization algorithms, called dithering, are employed on high-bit resolution images. The dithering process helps to remedy the problem, but it does not help much in terms of storage and transmission of images. To reduce storage needs and lower data transmission, numerous special compression techniques have been proposed in the last several decades. While the well-known compression algorithms, such as gzip, help lower image file sizes, usually, they are not adequate. To improve the compression gain, special compression techniques that take into account structure of image data must be developed. In this paper, we show that, when the pseudo-distance technique (PDT) is used for dithered images, it yields better compression results than GIF and PNG.