Joint Chroma Subsampling and Distortion-Minimization-Based Luma Modification for RGB Color Images With Application

In this paper, we propose a novel and effective hybrid method, which joins the conventional chroma subsampling and the distortion-minimization-based luma modification together, to improve the quality of the reconstructed RGB full-color image. Assume the input RGB full-color image has been transformed to a YUV image, prior to compression. For each <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> UV block, one 4:2:0 subsampling is applied to determine the one subsampled U and V components, <inline-formula> <tex-math notation="LaTeX">$U_{s}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$V_{s}$ </tex-math></inline-formula>. Based on <inline-formula> <tex-math notation="LaTeX">$U_{s}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$V_{s}$ </tex-math></inline-formula>, and the corresponding <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> original RGB block, a main theorem is provided to determine the ideally modified <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> luma block in constant time such that the color peak signal-to-noise ratio (CPSNR) quality distortion between the original <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> RGB block and the reconstructed <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> RGB block can be minimized in a globally optimal sense. Furthermore, the proposed hybrid method and the delivered theorem are adjusted to tackle the digital time delay integration images and the Bayer mosaic images whose Bayer CFA structure has been widely used in modern commercial digital cameras. Based on the IMAX, Kodak, and screen content test image sets, the experimental results demonstrate that in high efficiency video coding, the proposed hybrid method has substantial quality improvement, in terms of the CPSNR quality, visual effect, CPSNR-bitrate trade-off, and Bjøntegaard delta PSNR performance, of the reconstructed RGB images when compared with existing chroma subsampling schemes.