HEVC視窗視訊編碼之畫面內線型區塊複製與字串複製模式評比

Abstract

在高效能視訊壓縮（High Efficiency Video Coding，H.265/HEVC）的開發過程中，畫面內線型區塊複製模式（Intra Line Copy，ILC）與字串複製模式（Intra String Copy，ISC）為兩個能有效提升視窗視訊編碼效能的編碼工具。此兩模式皆以無失真資料壓縮之字串匹配演算法為基礎，但其設計與實作卻有相當顯著的差異。於本論文，為了探討畫面內線型區塊複製模式與字串複製模式的優劣，我們將針對兩模式之編碼效能進行評比，內容涵蓋壓縮效率、複雜度與記憶體存取頻寬三項。實驗結果顯示，兩模式之編碼效能相當且互有所長，畫面內線型區塊複製模式能有效提升自然與視窗影像混合視訊的編碼效能，而字串複製模式對於單純視窗視訊則有較佳的編碼表現；當考慮兩模式對於記憶體存取頻寬的影響，區域搜索相對於整張畫面搜尋較易實現於低延遲與即時的應用中。

Recently, Intra Line Copy (ILC) and Intra String Copy (ISC) have been introduced as effective means for screen content coding during the development of HEVC Screen Content Coding Extensions. Although conceptually sharing the same theoretical basis, which is essentially string matching, they differ from each other in a number of significant ways. This thesis presents detailed comparisons between them with respect to their compression performance, runtime complexity and memory access bandwidth, in order to better understand their merits and faults. Experimental results indicate that they perform comparably to each other, with ILC generally performing better in coding mixed content and ISC better in coding pure screen content. When considering their impact on the memory access bandwidth, local search for ILC/ISC becomes more favorable than full-frame search in low-delay real-time applications.