臺灣博碩士論文加值系統

視覺密碼是一種有效的影像加密方法。本篇論文中，我們提出了新的視覺密碼演算法，以達成不需像素擴展為目標，必且運用的有意義的圖像以作為分享影像。為了能達到原始秘密影像的視覺效果，我們定義了四個對比參數PSHb、PSHw、PSIb以及PSIw以控制分享影像及解密後影像的黑白對比。此外，我們亦利用不同的區塊大小選擇來控制所得分享影像的亮度及細節品質。針對(2, 2)、(2, n)以及(n, n)的視覺密碼演算法我們都提出了推導，並提供實驗結果驗證其效果。

Visual cryptography (VC) has been developed as an efficient image encryption method. In the thesis, we proposed a new visual cryptography algorithm to achieve non-pixel expansion VC using meaningful shares. To maintain the visibility of object in shares and secret image, we use four parameters PSHb, PSHw, PSIb and PSIw to set the contrast in the share images and the decrypted image. Also, we use different block sizes to control the brightness and quality of shares and decrypted image. The schemes of (2, 2), (2, n) and (n, n) are developed and experimental results shows the effectiveness of our visual cryptography algorithm.

ACKNOWLEDGEMENTS i
ENGLISH ABSTRACT ii
CHINESE ABSTRACT iii
TABLE OF CONTENTS iv
LIST OF FIGURES vi
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 VISUAL CRYPTOGRAPHY 3
2.1 THE MODEL OF (k, n) VISUAL CRYPTOGRAPHY 4
CHAPTER 3 RELATED WORKS 7
3.1 IMAGE SIZE INVARIANT VC 7
3.2 VISUAL CRYPTOGRAPHY USING PROBABILISTIC METHOD 8
3.3 APPLY TINY POPULATION GENETIC ALGORITHM TO VISUAL CRYPTOGRAPHY 10
CHAPTER 4 VISUAL CRYPTOGRAPHY USING MEANINGFUL SHARES 14
4.1 MEANINGFUL-SHARE VISUAL CRYPTOGRAPHY 14
4.2 MEANINGFUL-SHARE VC SCHEMES 17
4.3 SHARE GENERATING FOR (2, 2) VC USING MEANINGFUL SHARES 18
4.4 SHARE GENERATING FOR (2, n) VC USING MEANINGFUL SHARES 20
4.5 SHARE GENERATING FOR (n, n) VC USING MEANINGFUL SHARES 24
CHAPTER 5 RESULTS AND DISCUSSION 28
CHAPTER 6 CONCLUSIONS 33
REFERENCES 34

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