在這篇論文中，我們提出一個可用於視訊壓縮的快速區塊型動作計測演算法，其主要的搜尋過程是使用下坡式三角形搜尋。下坡是三角形搜尋包含兩個部分：初始三角形選定與下坡回圈。
　　在第一個部分，我們使用空間和時間上的相鄰區塊來幫助我們找到一個好的起始三角形。這個起始三角形的選定非常重要，會影響到計測結果的精確度與速度。在起始三角形決定好後，即進入第二部分，不斷地套用下坡式三角形搜尋的四種計算法則，以檢查新的位置，直到三角形滿足終止條件為止。最後三角形中擁有最小區塊差別值的點即為該區塊的動作向量。
　　我們將實驗結果分為兩個部分。第一個部分我們只套用動作計測和動作補償，以便直接觀察所找出的動作向量的精確度。第二部分我們則將動作計測整合到一個MPEG-4的參考程式中，以觀察所提出的方法在實際壓縮影片的時候需要的時間以及壓縮影片的品質。

In this thesis, we propose a fast block-based motion estimation algorithm which utilizes downhill simplex search for video coding. Downhill simplex search mainly consists of two parts: initialization of simplex part and downhill simplex iterations part.
In the initialization part, spatially and temporally neighboring blocks of the current block is used to help finding a good initial simplex. The initial simplex is essential to the whole process because it has great influences on the search time and accuracy. After the initial simplex is decided, the four actions of downhill simplex search are iteratively employed to check new points for substituting the high point of the simplex, until the stop criterion is satisfied. Finally, the point having the smallest distortion measure in the simplex is the motion vector.
The experiment contains two parts. In the first part, only motion estimation and compensation are applied in order to see the direct influence on the estimation accuracy. In the second part, we integrate the proposed motion estimation algorithm into an MPEG-4 sample codec to see the practical effects on both the time and quality.

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