Novel and Optimal Luma Modification-Based Chroma Downsampling for Bayer Color Filter Array Images

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 IBayer. Chroma downsampling is a necessary and important step in the coding system. In this paper, a novel and optimal luma modification-based chroma downsampling (LMCD) method is proposed for IBayer. For each converted 2 x 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.