Efficient Chroma Sub-Sampling and Luma Modification for Color Image Compression

In color image compression, the chroma components are often sub-sampled before compression and up-sampled after compression. Although sub-sampling the chroma components saves the bit-cost for compression, it often induces extra color distortions in the compressed images. In this paper, we propose two approaches to tackle this problem. First, we propose a sub-sampling method in the transform domain and apply it to both chroma components. Then, based on this sub-sampling, we propose a novel method to modify the luma component. In our proposed luma modification algorithm, the distortions that occurred in the two chroma components can be coupled together and utilized to modify the luma component. With our proposed chroma sub-sampling and luma modification algorithms, we can achieve a low RGB distortion in practical image coding. The experimental results demonstrate that our proposed methods offer more significant coding gains compared with the state-of-the-art methods for the compression of color images.