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Author: 許祖郡
Tsu-Chun Hsu
Thesis Title: 結合彩度抽樣和失真最小化的全彩影像重建及其應用
Joint Chroma Subsampling and Distortion-minimization for RGB Color Images with Application
Advisor: 鍾國亮
Kuo-Liang Chung
Committee: 蔡文祥
Wen-Hsiang Tsai
廖弘源
Hong-Yuan Liao
范國清
Kuo-Chin Fan
鍾國亮
Kuo-Liang Chung
姚智原
Chih-Yuan Yao
Degree: 碩士
Master
Department: 電資學院 - 資訊工程系
Department of Computer Science and Information Engineering
Thesis Publication Year: 2017
Graduation Academic Year: 105
Language: 英文
Pages: 31
Keywords (in Chinese): Bayer馬賽克影像 、彩度抽樣 、動態時間延遲積分影像 、失真最小化 、HEVC 、影像品質 、亮度調整 、RGB全彩影像
Keywords (in other languages): Bayer mosaic image, Chroma subsampling, Digital time delay integration image, Distortion-minimization, HEVC, Image quality, Luma modification, RGB full-color image
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    • 本篇論文提出將傳統彩度抽樣以及基於失真最小化的亮度調整做結合的一個新穎且有效的方法，來改善重建的RGB全彩影像的影像品質。壓縮前，我們先將彩圖從RGB色空間轉換到YUV色空間。對於每一個2×2的UV區塊，使用4:2:0彩度抽樣決定抽樣的U和V，Us、Vs。根據抽樣後的Us、Vs，以及對應的2×2原始的RGB區塊，本篇提供一個在O(1)時間調整2×2區塊亮度值的理論，使得原始的2×2RGB區塊和重建的2×2RGB區塊在CPSNR的品質量度之下的失真可以最小。此外，本篇方法以及理論亦可應用於動態時間延遲積分影像以及Bayer馬賽克影像。
    實驗結果顯示，在利用HEVC視訊壓縮標準來壓縮IMAX、Kodak及SCI影像時，本篇論文所提出的結合傳統彩度抽樣和基於失真最小化的亮度調整方法與現存的彩度抽樣方法相比，本篇方法不僅在重建的影像品質、視覺效果上有顯著的改善，而且品質與容量的權衡結果也是令人滿意的。

    In this thesis, we propose a novel and effective hybrid method, which joins the conventional chroma subsampling and the distortion-minimization based luma modification together, to improve the quality of the reconstructed RGB full-color image. Assume the input RGB full-color image has been transformed to a YUV image, prior to compression. For each 2×2 UV block, one 4:2:0 subsampling is applied to determine the one subsampled U and V components, Us and Vs. Based on Us and Vs, and the corresponding 2×2 original RGB block, a main theorem is provided to determine the ideal, i.e. globally optimal, modified 2×2 luma block in O(1) time such that the color peak signal-to-noise ratio (CPSNR) quality distortion between the original 2×2 RGB block and the reconstructed 2×2 RGB block can be minimized. Furthermore, the proposed hybrid method and theorem are adjusted to tackle the digital time delay integration images and the Bayer mosaic images. Based on IMAX, Kodak, and screen content test image sets, the experimental results demonstrate that in high efficiency video coding (HEVC), the proposed hybrid method has substantial quality improvement, in terms of the CPSNR quality, visual effect, and CPSNR-bitrate trade-off of the reconstructed RGB images when compared with existing chroma subsampling schemes.

    指導教授推薦書 i 論文口試委員審定書 ii 中文摘要 iii Abstract in English iv 誌謝 v Contents vi List of Figures viii List of Tables x 1 Introduction 1 1.1 Existing Chroma Subsampling Schemes 1 1.2 Motivation and Contributions 2 2 Transform Luma Modification to a Constraint Minimization Problem and a Nearoptimal Solution 4 2.1 Transform to a Constraint Minimization Problem 4 2.2 Near-optimal Solution and its Error Distribution 5 3 Main Theorem for Ideal Luma Modification and Appliction 9 3.1 Main Theorem for Ideal Luma Modification and Correctness Proof 9 3.2 Application to DTDI and Bayer Mosaic Images 13 3.2.1 Application to DTDI Images 13 3.2.2 Application to Bayer Mosaic images 15 4 Experimental Results 19 4.1 CPSNR Quality Merit 20 4.2 Visual Effect Merit 22 4.3 Quality-bitrate Trade-off Merit of the Proposed Hybrid Method 22 5 Conclusion 29 References 30

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