Abstract
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.
Highlights
T O REDUCE hardware costs, most modern digital color cameras, such as the Canon Ixus series, Nikon D series, Sony DSC-H50, Samsung NV15, and Agfa DC-504, are equipped with a single sensor covered with a Bayer color filter array (CFA) pattern [1] such that each CFA pixel contains only one color channel value
We explain why LMCDY21,Y2 is selected as the best choice, and it is called the optimal luma modification-based chroma downsampling (LMCD) method for chroma downsampling for
Note that FSIM [25] has two variants, namely FSIM and FSIMc, and FSIM is used for measuring the quality of the reconstructed Bayer CFA images; FSIMc is used for measuring the quality of the reconstructed RGB full-color images
Summary
T O REDUCE hardware costs, most modern digital color cameras, such as the Canon Ixus series, Nikon D series, Sony DSC-H50, Samsung NV15, and Agfa DC-504, are equipped with a single sensor covered with a Bayer color filter array (CFA) pattern [1] such that each CFA pixel contains only one color channel value. The above-mentioned traditional method performs chroma downsampling on Bcon,YUV directly, but it fails to consider the input Bayer CFA pattern, limiting the quality of the reconstructed images. At the server side, we deploy a bilinear interpolation-based upsampling process to better estimate the four upsampled (U, V)-pairs of Brec,UV , in terms of Ud, and Vd. combining luma modification and chroma downsampling together, we propose a novel LMCD method, called LMCDy|y|, in which y denotes one element in the power set of {Y1, Y2, Y3, Y4}, such that the luma values in y of Bcon,Y can be modified to cooperate with Ud and Vd for improving the quality of the reconstructed images.
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