A Coordinate Displacement Compensation Based Quality Enhancement Method
for Chroma Subsampling and Upsampling on VVC
Abstract
Prior to encoding an input RGB full-color image IRGB,
at the server side, performing chroma subsampling on the converted
chroma image is a necessary step. After receiving the decompressed
subsampled chroma image and luma
image at the client side, performing chroma upsampling is also a
necessary step for reconstructing the RGB full-color image. In this
paper, we consider seven commonly used chroma subsampling methods,
denoted by Cs, and four widely used chroma upsampling
methods, denoted by Cu. For each combination
cs-cu in
CsxCu, we first utilize the moment
balance law to analyze the coordinate displacement (CD) bias problem
occurring in cs. Next, for the combination
cs-cu, we analyze the CD bias problem
occurring in the transition from the server side to the client side.
Then, we explain why the CD bias problem degrades the quality of the
reconstructed RGB full-color images in the current coding system. To
remedy this CD bias problem, a CD compensationbased (CDC-based) quality
enhancement method is proposed to improve the quality of the
reconstructed images. To the best of our knowledge, this is the first
work in this research direction. Based on the IMAX, Kodak, SCI (screen
content images), and Video datasets, the comprehensive experimental
results have demonstrated that on the newly released versatile video
coding (VVC) platform VTM-12.0, the proposed CDC-based quality
enhancement method in our augmented coding system can achieve
substantial quality improvement for 17 combinations in
CsxCu.