Effective Chroma Subsampling and Luma Modification for RGB Full-Color Images Using the Multiple Linear Regression Technique

Abstract

Differing from the traditional chroma subsampling on the YUV image converted from a RGB full-color image, in this paper, we propose a novel and effective chroma subsampling and luma modification (CSLM) method. For each 2×2 YUV block, first, a newly reconstructed 2×2 RGB full-color block-distortion model is proposed, and then we propose a multiple linear regression approach to tackle our CSLM method such that the reconstructed 2×2 RGB full-color block-distortion can be minimized, achieving significant quality improvement of the reconstructed RGB full-color image. Based on the Kodak and IMAX datasets, the comprehensive experimental results demonstrated that on the versatile video coding (VVC) platform VTM-8.0, our method achieves substantial quality and quality-bitrate tradeoff improvement of the reconstructed RGB full-color images relative to six traditional methods and the three state-of-the-art methods.

A Reduced Codebook and Re-Interpolation Approach for Enhancing Quality in Chroma Subsampling

“…A. Quality Enhancement Merit of Our RCRI Approach for 𝐼 𝑅𝐺𝐵 For 𝐼 𝑅𝐺𝐵 , this subsection presents the quality enhancement effects of our RCRI approach against the UPI and true CI problems for the traditional and state-of-the-art combinations [43], [33], and [4]. In the five traditional chroma subsampling methods, 4:2:0(L) and 4:2:0(R) are selected to balance our discussion of the experiments.…”

“…4. Based on the subsampled chroma parameter-pair located at ( 1 2 , 1 2 ), the CSLM [4] and 𝐶𝑆𝐿 𝑀 𝐵𝑎𝑦𝑒𝑟 [8] methods apply the BILI-based chroma upsampling process to estimate the four chroma pairs of each 2×2 chroma block 𝐵 𝐶𝑏𝐶𝑟 for building up their own block-distortion functions. Therefore, the subsampled chroma position of the two methods is expressed as ( 12 , 1 2 ).…”

“…We first introduce the five traditional chroma subsampling methods, namely 4:2:0(A), 4:2:0(L), 4:2:0(R), 4:2:0(DIRECT), and 4:2:0(MPEG-B) [28]. Then, we introduce five state-of-the-art chroma subsampling combinations [43], [33], [4], [22]. According to the new edge-directed interpolation (NEDI) [19] based chroma upsampling process which improved the previous method [1], Zhang et al [43] proposed an interpolation-dependent image downsampling (IDID) based chroma subsampling method.…”

“…Differing from the the chroma subsampling-first luma modification method [5], in [4], based on the subsampled chroma parameter-pair, at the server side, a BILI-based chroma estimation of 𝐵 𝐶𝑏𝐶𝑟 is deployed in the block-distortion function with two chroma parameters and four luma parameters. Next, using a multiple linear regression technique, a joint chroma subsampling and luma modification (CSLM) method [4] was proposed to determine the subsampled (𝐶𝑏, 𝐶𝑟)-pair of 𝐵 𝐶𝑏𝐶𝑟 and the four modified luma values of 𝐵 𝑌 simultaneously. Their combination is expressed as CSLM-BILI.…”

“…Without the loss of generality, we take the CSLM-BILI combination [4] as the example to define the UPI problem.…”