Adaptive low complexity colour transform for video coding

For video compression, the RGB signals are usually converted at the source to a perceptual colour space, followed by chroma sub-sampling, for coding efficiency. This is based on the typically higher human visual system sensitivity to the luminance than chrominance of image signals. However, there are specific applications that demand carrying the full RGB signals through the transmission chain, which may also benefit from lossless colour transforms, for efficient coding. In either case, the best colour transform function is noted to be content dependent, although fixed transforms are typically adopted for convenience. This paper presents a method of dynamically adapting this colour transform function for each picture block, using a class of low complexity lifting based schemes. The performance of the proposed algorithm is compared with a number of fixed colour transform schemes and shows a significant compression gain over native RGB coding and YC_oC_g transform.