臺灣博碩士論文加值系統

在這篇論文中，我們提出了一個使用離散餘弦轉換(Discrete Cosine Transform DCT) 架構的邊緣偵測(Edge Detector)系統。這個系統可以提供給影像縮減(down-sample)時使用。我們先將原影像分割成不重疊的區塊，區塊的長度等於縮減系數(decimation factor)。並在每一個區塊中作 DCT 運算。用每一個區塊中的 DCT 系數中所有 AC 系數的變異數(Variance)作為新的 edge map 中的 pixel 值的判斷依據。 我們亦可以使用 2-D DCT 系數的特性，將所提出的方法使用在方向性的邊緣偵測系統。 根據我們模擬的結果，我們提出的 DCT-based edge detector 的表現較傳統的方式在 PSNR 的比較上有較佳的表現。

In this thesis, we propose a discrete cosine transform (DCT)-based edge detector for snapshot images that are obtained by performing decimation (by a factor of two or more) on a much larger original image. We first partition the original image into non-overlapping blocks where the block size equals the decimation factor and then perform DCT on each block. The variances of the DCT’s AC coefficients are used to decide the edge map of snapshot images. Directional edge map of the snapshot images can also be generated if the variance of the directional AC coefficients in vertical, horizontal, or diagonal direction is used. Simulation results show that the proposed DCT-based edge detector performs better (based on objective PSNR criterion) than the conventional technique─applying edge detector on the down-sampled image.

Chapter 1 1
Introduction 1
1.1 起源： 1
1.2 Sampling Theorem 1
1.3 前人解決的方法與限制 4
Chapter 2 6
Discrete Cosine Transform 6
2.1 DCT 的數學意涵： 6
2.2 DCT Coefficients 的特性 8
2.3 Fast DCT 9
Chapter 3 14
Proposed Method 14
3.1 Main Innovation： 14
問題一： 15
問題二： 16
3.2 Proposed Method 19
3.3 Mapping Algorithm and Sorting 23
3.3.1 Linear conversion 24
3.3.2 Logarithm conversion 26
3.3.3 Histogram Equalization 29
Chapter 4 31
Simulation Result 31
4.1 Simulation Result 31
4.2 PSNR Comparison 38
Case 1： 39
所有的調整 Dynamic Range 動作皆使用 Logarithm Method 39
Case 2： 41
所有的調整 Dynamic Range 動作皆使用 Histogram Equalization 41
Case 3： 44
所有的調整 Dynamic Range 動作皆使用 Linear Method 44
4.3 Directional Edge Detector 46
Chapter 5 48
Discussion 48
5.1 Mask Size Problem 48
5.2 White Gaussian Noise Influence 51
Case 1：只有WGN 存在時，會有何影響？ 52
Case 2：WGN與 Signal都存在時，會有何影響？ 52
Chapter 6 54
Conclusion 54
Chapter 7 55
Reference 55
Index A 57
Accepted by ISCAS 2002 57

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