A new color transform for RGB coding

This paper presents a new color transform (YSbSr) that increases the coding efficiency for RGB space by reducing the conversion error and coding error propagation that happen during the color space conversion. Traditionally the use of color transforms has been limited to maintain the compatibility with black-and-white transmission. But for high quality video for professional applications, the focus should change accordingly. Recently during the course of development for Professional Extensions of the MPEG-4 AVC H.264 standard, new color transforms have been proposed. These transforms are focusing on the decorrelation and reversibility using a lifting scheme for integer implementation. But in a real coding scenario, lossless coding is rare and coding error is inevitable. So we have to deal with the propagation of coding error due to the backward conversion to RGB space. Even though integer mapping is a charming factor, it is more desirable not to employ integer mapping if we lose the original goal, high decorrelation gain with small conversion error. Since the conversion equation takes up a very small portion of coder complexity, the difference between integer mappings and floating point operation is diluted. Based on this observation, we propose a new color transform that gives: high decorrelation gain with small rounding and conversion error. The simulation results show that we can achieve almost up to 2 dB gain compared with the traditional YCbCr color space using the proposed transform. It makes the proposed color transform a good candidate for applications that need to preserve the original color fidelity.