利用運算重排發揮H.264中去方塊濾波器的平行度

Abstract

在H.264影像壓縮標準中，去方塊濾波器的計算量大約占整體解碼器的三分之一。隨著多工處理器將成為未來系統設計的趨勢，若可把去方塊濾波器內的運算良好的分配到各個處理單元，則可以省下計算時間。在這篇論文中，我們提出了兩個粒度來做平行處理的單位，第一是H.264去方塊濾波器所使用的基本單位16像素長的邊，第二是根據分析去方塊濾波器所能達到的最高平行度所使用的最小基本單位4像素長的邊。此外，在此篇論文中我們提出一個方法使得在硬體資源受限的情況下，盡可能地充分利用所擁有的硬體資源，以及符合我們設計所需要的去方塊濾波器硬體需求。在硬體無限制下，對1920×1080與1080×1920這兩種形狀的圖片做去方塊濾波，16像素長的邊這個粒度的處理順序與二維波前方式所提出來的處理順序相比所得到的加速分別為1.57與2.15倍，4像素長的邊這個粒度的處理順序與二維波前方式所提出來的處理順序相比所得到的加速分別為1.92與2.44倍。另外，我們的方法可使處理時間成正比於圖片大小的平方根(在一樣的圖片長寬比下)。

In the H.264 video compression standard, the deblocking filter contributes about one-third of all computation in the decoder. With multi-processor architectures becoming the future trend of system design, computation time reduction can be achieved if the deblocking filter well apportions its operations to multiple processing elements. In this paper, we apply a 16 pixel long boundary, the basic unit for deblocking in the H.264 standard and a 4 pixel long boundary as the basis for analyzing and exploiting possible parallelism in deblocking filtering. Moreover, a possible compromise to fully utilize limited hardware resources and hardware architectural requirements for deblocking are also proposed in this paper. Compared with the 2D wave-front method order for deblocking both 1920*1080 and 1080*1920 pixel sized frames, the 16 pixel long boundary method gains speedups of 1.57 and 2.15 times given an un-limited number of processing elements respectively, and the 4 pixel long boundary method gains speedups of 1.92 and 2.44 times given an un-limited number of processing elements respectively. Using this approach, the execution time of the deblocking filter is proportional to the square root of the growth of the frame size (keeping the same width/height ratio), pushing the boundary of practical real-time deblocking of increasingly larger video sizes.