傳統上，在壓縮 RGB 全彩圖像之前，對於每個轉換成的 2$\times$2 CbCr 區塊 $B^{CbCr}$，色度下採樣僅對 $B^{CbCr}$ 進行下採樣，但不會更改亮度塊 $B^{Y}$。在目前的研究中，一種特殊的基於線性插值，即基於COPY的色度二次採樣優先亮度修改（CSFLM）研究試圖改變亮度塊以提高重建RGB全彩圖像的質量。在本文中，提出了一種快速有效的非線性插值，即雙三次卷積插值（BCI），基於CSFLM的迭代亮度修改方法。在我們的迭代方法中，首先提供了一個基於 BCI 的失真函數及其凸屬性證明。接下來，在提出的凸性失真函數的基礎上，應用偽逆技術獲得初始亮度修正解，然後提出了一種迭代方法來改進初始亮度修正解。基於IMAX、柯達、SCI（屏幕內容圖像）、CI（經典圖像）和視頻數據集五個測試圖像數據集，徹底的實驗結果表明，在新發布的多功能視頻編碼（VVC）平台VTM-12.0 中，與現有的最先進方法相比，我們的迭代亮度修改方法實現了顯著的質量、執行時間和質量比特率權衡改進。

Traditionally, prior to compressing an RGB full-color image, for each converted 2$\times$2 CbCr block $B^{CbCr}$, chroma subsampling only downsamples $B^{CbCr}$, but without changing the luma block $B^{Y}$ at all. In the current research, a special linear interpolation-based, namely the COPY-based, chroma subsampling-first luma modification (CSFLM) study has attempted to change the luma block for enhancing the quality of the reconstructed RGB full-color image. In this thesis, a fast and effective nonlinear interpolation, namely the bicubic convolution interpolation (BCI), based iterative luma modification method for CSFLM is proposed. In our iterative method, a BCI-based distortion function and its convex property proof are first provided. Next, based on the proposed convex distortion function, a pseudoinverse technique is applied to obtain the initial luma modification solution, and then an iterative method is proposed to improve the initial luma modification solution. Based on five testing image datasets, namely the IMAX, Kodak, SCI (screen content images), CI (classical images), and Video datasets, the thorough experimental results have demonstrated that on the newly released Versatile Video Coding (VVC) platform VTM-12.0, our iterative luma modification method achieves substantial quality, execution-time, and quality-bitrate tradeoff improvements when compared with the existing state-of-the-art methods.

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