Chroma scaling for high dynamic range video compression
Color pixel encoding optimizes the conversion of linear physical values of light into integer values. The efficiency of such encoding methods depends on a trade-off between the bit-depth used and the visible distortion introduced by quantization. This efficiency for different color pixel encoding approaches has been evaluated in literature, without considering the fact that before transmission to the end-user, color encoded content needs to be compressed using a video codec. Thus, to be efficient, a color pixel encoding scheme needs not only to achieve the lowest bit-depth, but also to allow for efficient video compression ratio. Yet, when compressing dark video sequences, the most efficient color pixel encoding scheme known as Y'DuDv requires much higher bit-rates, hence negating its high encoding efficiency. In this article, we propose a chroma scaling technique that adaptively restricts the bit-depth of the chroma channels for optimized encoding of High Dynamic Range content. Results show that the proposed scaling reduces Y'DuDv bit-rate requirements for dark content while preserving its high color accuracy.