Differing from the traditional chroma subsampling on the YUV image converted from a RGB full-color image, in this paper, we propose a novel and effective chroma subsampling and luma modification (CSLM) method. For each 2×2 YUV block, first, a newly reconstructed 2×2 RGB full-color block-distortion model is proposed, and then we propose a multiple linear regression approach to tackle our CSLM method such that the reconstructed 2×2 RGB full-color block-distortion can be minimized, achieving significant quality improvement of the reconstructed RGB full-color image. Based on the Kodak and IMAX datasets, the comprehensive experimental results demonstrated that on the versatile video coding (VVC) platform VTM-8.0, our method achieves substantial quality and quality-bitrate tradeoff improvement of the reconstructed RGB full-color images relative to six traditional methods and the three state-of-the-art methods.

The Bayer color filter array (CFA) pattern has been widely used in modern digital color cameras, and the captured image is called the Bayer CFA image I Bayer. Chroma downsampling is a necessary and important step in the coding system. In this paper, a novel and optimal luma modificationbased chroma downsampling (LMCD) method is proposed for I Bayer. For each converted 2 × 2 YUV block, the downsampled (U, V)-pair and the modified luma values by the proposed LMCD method can be optimally determined, and the optimal variant of our LMCD method associated with the two modified luma values has the best quality among all sixteen variants of LMCD. Based on the Kodak and IMAX datasets, on the High Efficiency Video Coding (HEVC) platform HM-16.18, the Versatile Video Coding (VVC) platform VTM-8.0, and the Joint Photographic Experts Group (JPEG) platform, the comprehensive experimental data showed the substantial quality and quality-bitrate tradeoff merits of the reconstructed images by our optimal LMCD method relative to the traditional and state-of-the-art chroma downsampling methods.

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