Abstract
The images obtained by the camera sensors are stored in the format of CFA, Color Filter Array, which only contains limited information about the R, G, and B signals of images. The images in CFA are upsampled into RGB 444 format by demosaicking algorithms, converted into YCbCr 444, then chroma-downsampled into YCrCb 420 format for image/video compression. In this paper, a novel chroma-downsampling method is developed to improve a state-of-the-art method. The optimization problem for the proposed method considers more factors and provides a better closed-form solution for the optimally sampled chroma values. Reversely in the decoder, a chroma-upsampling method is required for the image reconstruction. In the proposed chroma-upsampling method, the neighboring chroma pixels and their distances to the recovered pixel are considered; the procedure is to produce weightings to redistribute the total pixel values in the original estimates. Combining the proposed chroma-downsampling and the proposed chroma-upsampling works, the proposed method outperforms the state-of-the-art method by BDPSNR (Bjontegaard Delta peak signal-to-noise ratio) 0.3161 for H.264/AVC, 0.3845 for HEVC (High Efficiency Video Compression) and 0.3739 for VVC (Versatile Video Coding), averaged over all tested videos and all 7 different considered CFA formats.
Published Version
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