低複雜度無失真視訊壓縮

Abstract

本篇論文提出一個適應性無失真視訊壓縮演算法，以”行(line)”為處理單元，擁有低複雜度、延遲時間短的特性，可應用於互動式多媒體。對於高解析度視訊的傳輸及儲存裝置間的資料交換，為了減少傳輸所需的頻寬及節省儲存空間，同時又不造成資料的誤差，無失真的視訊壓縮演算法是必要的。考慮多媒體應用之低複雜度及低延遲的需求，我們提出低複雜度無失真視訊壓縮演算法(Line-based Lossless Video Compression, LALVC)。低複雜度無失真視訊壓縮演算法LALVC具有以下特性—單次資料分析(one-pass)處理，以掃瞄的順序(raster-scan order)處理，不採用轉換(transformation)而只用簡單的本文預測法(Context based predictors)，同時兼顧時間及二維圖形中的關係來做有效的編碼。在時間軸上的圖像關係，採用零動量(zero-motion)的預測法來除去多餘資料以達到高效率的視訊壓縮。此外針對自然影像及電腦圖形的特性不同，利用不同模式的處理，透過一個簡單而有效的模式判定(mode decision)，來提升編碼的效率。另外entropy 編碼方法採用Golomb code—同樣具有低複雜度，又有很高的編碼效率，且易於用硬體實現。LALVC演算法經由摸擬的結果，在時間軸上的預測法，搭配”行”為處理單元的視訊編碼方法，可以有效地提升壓縮效率。計算量上，相對於影像無失真演算法JPEG-LS，雖僅增加了些加法運算，即可有效地提升整體的編碼效率，且達到即時壓縮的效果。同時為了展示LALVC演算法的硬體實現與即時視訊壓縮，本論文也利用ASIC晶片設計方式實現了LALVC演算法的硬體架構。

We present a line-based adaptive lossless video compression (LALVC) algorithm for interactive multimedia applications that demand low complexity and low latency. Communications between high-resolution display and storage devices require high bandwidth for exchanging raw data. To reduce the cost of video transmission without losing data accuracy, a lossless video compression is necessary. Considering low complexity and low delay, the proposed LALVC adopts a simple and yet efficient architecture that consists of one-pass, raster-scan, transform-free coding process with a simple predictor. For low latency, zero-motion prediction and single frame buffer are used to reduce temporal redundancy. In addition, to maximize the coding efficiency for both natural and computer-generated video sequences, LALVC adaptively selects the best coding mode for each line in a frame. The entropy coding of each line is based on Golomb code to enhance coding efficiency with less computation load and is easy for hardware realization. The simulation results show that temporal preprocessing and line-based mode decision of LALVC can increase compression ratio with properly increased complexity as compared to that of JPEG-LS. In addition, to demonstrate easy hardware realization and real-time video compression, we realize hardware architecture of LALVC for ASIC design.