A Low Complexity ALF based on Inter-Channel Correlation between Chroma and Luma in HEVC

Wei-Jing Chen, Lei Sun, Lei Gu, Zhen-yu Liu, and Takeshi Ikenaga


HEVC, Inter-Channel Correlation, ALF


The adaptive loop filter (ALF) is a Wiener algorithm based technology which is applied to the reconstructed frame to improve the image quality in high-efficiency video coding (HEVC). In the conventional ALF algorithm, filter coefficients are re-designed for 16 times to obtain the best sets in one frame and also to increase the external memory access and computational cost significantly. This contribution proposes an inter-channel transformation scheme based on the correlation between chroma and luma to alleviate both computing time and memory bandwidth. First, the proposed algorithm generates the cross-correlation matrix and auto-correlation matrix in chroma samples which only spends one-quarter computational costs due to the resolution difference. Then, it applies the inter-channel transformation to derive the filter coefficients. The proposed methods not only eliminate a large number of multiplication operations, but also reduce the run-time by 58.70% averagely during whole ALF encoding process, while a negligible loss 0.074 BD-PSNR in the Y component.

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