在這篇論文中，我們提出了新的形狀編碼演算法，包括了畫面內(Intra)與畫面間(Inter)兩種模式，它們都是以鏈碼(chain code)為根本改進而成的。一個物體的輪廓若以鏈碼來表示，就可以根據平滑程度來將它分做好幾段，根據這個特性，這裡提出的畫面內與畫面間模式下的方法使用了一些技巧來達成形狀編碼的目的。在畫面內模式下，每個段落使用一些特殊的碼來編碼壓縮，解碼的結果是無失真的。我們的畫面內模式下的方法與MPEG-4、M4R、鏈碼與差值鏈碼經過實驗比較之下，壓縮的效果是較好的。另外，在畫面間模式下，我們提出了新的編碼流程，流程包括了在一個以鏈碼表示的物體中尋找斷裂點(break point)，再尋找斷裂點的關聯性，最後將一段鏈碼做細微縮放的處理使它與另一段鏈碼更相似，並判斷相似的程度是否在我們容忍的範圍內。只要做畫面內模式的編碼，所有的斷裂點都會被找到；藉著計算兩個相似輪廓上的點的曲率差值，我們就可以找出它們的關聯性；而縮放則是將一段鏈碼延長或縮短的技巧。我們實驗的結果顯示了不管是在高失真或低失真的情形下，我們提出的方法的壓縮率都比MPEG-4的方法更理想。

In this paper, new intra and inter shape coding algorithms are proposed. The new algorithms are based on chain code. Chain code of an object's contour can be divided into several segments by the smooth contour characteristic. By this property, some techniques can be used for the proposed intra and inter shape coding algorithms. In intra mode, each segment is encoded by specific codes, and the decoding result is lossless. Compared with MPEG-4, M4R, DCC and chain code, the compression ratio is improved. Besides, a new coding scheme is proposed for the inter shape coding. It includes finding break points in a series of chain code, correlation between break points and fine scaling with a tolerant threshold between two similar chain code segments. By detecting the segments, break points can be found. The correlation is performed by computing the curvature difference between break points and contour points. The scaling is a technique for extending or shrinking a segment of chain code. Experimental results show that in the condition of high quality or low bit rate our proposed inter shape coding algorithm obtains better performance than MPEG-4 in compression.

1. Introduction 1
2. Background Materials of Binary Shape Coding 6
2.1 M4R 6
2.1.1 Intra Shape Coding 7
2.1.2 Inter Shape Coding 11
2.2 MPEG-4 13
2.2.1 BAB_type 13
2.2.2 Size conversion 14
2.2.2.1 Down-sampling 15
2.2.2.2 Up-sampling 15
2.2.3 Context-based arithmetic encoding (CAE) 17
2.2.4 Decision Pseudo Code 19
2.3 Chain code 21
2.4 Differential chain code 22
3. Proposed algorithms 23
3.1 Intra shape coding 23
3.2 Inter shape coding 25
4. Experiments and Discussion 32
4.1 Experiments 32
4.2 Discussion 46
5. Conclusion 47
REFERENCES 48

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