架構於H.264/AVC之有效率區塊大小模式決策演算法

Abstract

由於近幾年數位電視系統的興起與普及，使得對於視訊影片的品質要求愈來愈高。加上網路的方便性與頻寬限制性，促使了新的視訊壓縮標準H.264/AVC的制定。在新的標準H.264中，雖仍延用預測、轉換、量化和entropy編碼四大部份，但H.264是在各個部份中都採取許多新技術與觀念，以達到高壓縮效能。相較於過去的標準，H.264節省了50%的空間儲存，但其運算複雜度卻是太高，尤其是在做區塊大小模式決策時。因此，在這篇論文中，我們提出一演算法來改善H.264編碼器的效能。在提出的演算法中，利用了幾項可用資訊，包括了靜態區域、殘餘資料以及運動向量關係此三種，有效的利用此三項資訊可以有效率加快區塊大小模式之決策，以致於達到改進編碼器效能的目的，以降低整個壓縮系統的複雜度。由實驗結果顯示，與暴力法來決定區塊模式的方法比較，本論文提出之演算法可達到增進50%的整體編碼時間，且可不影響視訊影片品質，只約增加了1.5%的位元率。除此之外，本論文亦與最近幾年裡已發表的區塊模式決策方法相互比較，並於實驗結果中，可明顯看出本論文提出之方法可更有效的改進模式決策之效能。

The new video coding standard, H.264/MPEG-4 Part10, provides some new features to get average bit rate reduction of 50% compared to any other standard under given fixed fidelity. One of these features is to allow using variable block-size motion compensation with small block sizes. In the reference software JM8.2, the exhaustive search for variable block-size mode selection is adopted, this is very time consuming. Here, we will propose a fast method to find a suitable block size for each macro-block in inter prediction. The proposed method uses some information, such as still area, residue image after motion search, and the relation of motion vectors, to reduce the number of possible block-size modes in the variable block-size mode decision. The experimental result shows that this new scheme could reduce about 50% total encoding time while keeping the same quality and a mere 1.51% bit-rate increase compared to the exhaustive search scheme. Besides, we also compare the efficiency among our method and some exiting methods. The experimental result shows that our algorithm is faster than others.