Comparative study of color transforms for image coding and derivation of integer reversible color transform

Abstract

A color transform is necessary for better color image coding. In this paper, we concentrate on a comparative study of color transforms for color image coding in order to find the best one among 11 published color transforms: YCrCb, NTSC, PAL, HDTV, WW, XYZ, DCT, DHT, two approximate K-L transforms (K1K2K3 and KLT) and the original reversible color transform (ORCT) adopted in JPEG-2000. Experiment results with JPEG-2000 verification model (VM5.1) are sorted by color transforms and counted up for all the test images and diverse bit rates. The sorting scoring table shows that the discrete cosine transform performs best among 11 tested color transform at 6 lossy bit rates for all the 2 JPEG-2000 color test images and other 23 color images we used. Then we derive an integer reversible transform of DCT and an approximate implementation using additions and shifts only for both lossless and lossy color image coding. Experiments with the integer reversible color transforms show that the proposed transform scheme is better than ORCT for lossy image coding.