由於HDR影像提供了10 bits於更廣泛的色彩空間之中，相較於SDR影像能帶來更高的影像品質。壓縮之前，HDR影像會先進行色空間轉換，轉成Y'CbCr或是ICtCp影像，並對彩度平面進行抽樣，也就是說CbCr和CtCp影像。首先，我們提出一基於雙三次插植法的區塊失真函數(Bicu-based區塊失真函數)，以測量原圖之2×2區塊與預測之2×2區塊之平方差之和，我們接著證明提出的BICU-based區塊失真函數是一凸函數，並提出一基於此函數的迭代演算法以優化預估出的2×2抽樣區塊。實作於VVC壓縮平台(版本:VTM 11.0)，基於四個測試序列，綜合的實驗結果證明，與現有的方法相比，使用提出的BICU-based迭代彩度抽樣演算法，可以顯著的提高重建後的HDR影像品質，並在品質-Bitrate之間取得良好平衡。

Owing to offering 10 bits per pixel in a broader color space, high dynamic range (HDR) images provide higher quality than standard dynamic range (SDR) images. Prior to compression, the input HDR image is converted to a Y'CbCr image or an ICtCp image, and then chroma subsampling is performed on the converted chroma image, i.e. the CbCr or CtCp image. We first propose a bicubic interpolation-based (BICU-based) block-distortion function to measure the sum of square errors between one 2×2 ground truth HDR block and the 2×2 estimated HDR block. Next, we prove that the proposed BICU-based block-distortion function is a convex function. Further, a convex function minimization-based iterative algorithm is proposed to optimize chroma subsampling for each 2×2 chroma block. Based on four HDR test sequences and on the Versatile Video Coding (VVC) platform VTM-11.0, the comprehensive experimental results have justified the significant quality enhancement and quality-bitrate tradeoff merits of the reconstructed HDR images using our BICU-based iterative chroma subsampling algorithm when compared with the existing methods.

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