New simple and efficient color space transformations for lossless image compression

• New transformation requiring 4 operations per pixel gave the best overall ratios.
• New transformation done in 2 operations gave the best JPEG2000 and JPEG XR ratios.
• A transformation from human vision system outperformed established ones.
• PCA/KLT resulted in ratios inferior to ratios of new and established transformations.

We present simple color space transformations for lossless image compression and compare them with established transformations including RCT, YCoCg-R and with the optimal KLT for 3 sets of test images and for significantly different compression algorithms: JPEG-LS, JPEG2000 and JPEG XR. One of the transformations, RDgDb, which requires just 2 integer subtractions per image pixel, on average results in the best ratios for JPEG2000 and JPEG XR, while for a specific set or in case of JPEG-LS its compression ratios are either the best or within 0.1 bpp from the best. The overall best ratios were obtained with JPEG-LS and the modular-arithmetic variant of RDgDb (mRDgDb). Another transformation (LDgEb), based on analog transformations in human vision system, is with respect to complexity and average ratios better than RCT and YCoCg-R, although worse than RDgDb; for one of the sets it obtains the best ratios.