Adjusted 4:2:2 chroma subsampling strategy for compressing mosaic videos with arbitrary RGB color filter arrays in HEVC

Abstract

To reduce the cost, most of surveillance cameras and web cameras are equipped with a single sensor covered by a red-green-blue (RGB) color filter array (CFA) for capturing only one RGB color component per pixel and hence produce so-called mosaic images. Conventionally, such cameras perform demosaicking, the transform from RGB domain to YUV domain, the chroma subsampling with 4:2:2 format, and the video coding to compress the captured mosaic images for storage saving and transmission over the Internet. However, in the conventional compression scheme, the commonly used 4:2:2 chroma subsampling strategies always sample U and V components from the fixed positions without considering the significance of the sampled U and V components for reconstructing R, G and B pixels, which results in the quality degradation of the reconstructed videos. In this paper, to remedy this weakness, we propose an adjusted 4:2:2 chroma subsampling strategy for compressing mosaic videos with arbitrary RGB-CFA structures in HEVC. The novelty of our work lies on that the positions of the sampled U and V components are dynamically adjusted according to the ordered significance of the U component for reconstructing B and G pixels as well as the V component for reconstructing R and G pixels. Experimental results demonstrate that the proposed adjusted 4:2:2 chroma subsampling strategy outperforms, in terms of the quality of the reconstructed mosaic videos and the reconstructed full-color videos, the commonly used ones in the cases of middle and high bitrate and is competitive with the commonly used ones in the case of low bitrate.