視訊會議標準 H.261 的研究

Abstract

本論文完成一個符合視訊會議標準 H.261 的系統。在 H.261 標準中有許 多部分是可以隨程式設計者以不同的方法來完成。在本論文中採用了一個 快速的離散餘弦轉換(DCT/IDCT)的演算法，減少所需要的運算。在移動預 估上，除了採用 3-step 搜尋法之外，另外加入了一些小技巧如 partial error，及考慮了畫面上靜止和移動的物體的特性等以加速搜尋過程。而 在強制更新上，亦提出了一種能符合 H.261 標準要求的方法。 A system following the video conference standard H.261 isimplemented in this thesis. H.261 is a compromise betweencoding performance, real-time requirement, implementation complexity and system robustness. It consists of some mainparts: DCT/IDCT, quantization/inverse quantization, variablelength coding, BCH code and motion estimation. Although H.261has given many rules for encoder and decoder, there are manyparts in which we can develop some algorithms to improve theimage quality and coding speed. In this thesis, we adopt afast DCT/IDCT algorithm to reduce the computation. In motionestimation, we propose a algorithm which is based on 3-step search. The algorithm uses the fact that partial error isalways less than total error, and the characteristics ofstill blocks and motion blocks to reduce the search time.Based on the characteristic of still blocks, it can eliminateup to 80% of the 3-step search. Based on the characteristicof motion blocks, it can quickly find a matching block.Besides, an algorithm is provided to guarantee fitting therequirement of force updating in H.261.