Interpolative, predictive and pyramid transform coding of color images

Three methods are investigated for improving the image quality obtainable by transform coding at relatively low bit rates. Coefficients are transmitted in the so-called zig-zag scanning order, which approximates an ordering according to increasing spatial frequency. For most blocks, coefficients higher than a certain order all have zero quantized value. These are not sent. Instead an end-of-block word is transmitted to indicate to the receiver that the remaining quantized coefficients of that block were zero. Interpolative transform coding requires side information, whereas predictive transform coding does not. Pyramid transform coding performs the best, but at the expense of considerable additional signal processing