視覺密碼之色彩管理與立體顯示應用｜國立臺灣科技大學博碩士論文系統

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研究生：	蔡世龍 Shih-lung Tsai
論文名稱：	視覺密碼之色彩管理與立體顯示應用 Color Management and Stereoscopic Display Application of Visual Cryptography
指導教授：	溫照華 Chao-hua Wen
口試委員:	孫沛立 Pei-li Sun 陳鴻興 Hung-shing Chen 歐立成 Li-chen Ou 廖怡欽 Yi-ching Liaw
學位類別：	碩士 Master
系所名稱：	應用科技學院 - 應用科技研究所 Graduate Institute of Applied Science and Technology
論文出版年：	2012
畢業學年度：	100
語文別：	英文
論文頁數：	80
中文關鍵詞：	視覺密碼學、視覺密碼分享圖、立體顯示器、像差
外文關鍵詞：	Visual cryptography, Visual cryptography scheme, Stereoscopic display, Disparity
相關次數：	點閱：290 下載：4
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視覺密碼學是一種影像加密技術，可以將視覺資訊的資料加密，而利用人類視覺系統進行解密，不須經過複雜的計算。在製作視覺密碼時，解密端使用者往往使用不同於加密端的顯示器型號。其中色域（Color gamut）是一種影像再現媒體的色彩特徵範圍，其扮演一個關鍵角色如何將特定秘密圖像在最終的解密影像呈現在人類眼前。隨者科技的演進，各種廣色域顯示器現在已佔據特定專業領域市場，甚至走入家庭劇院裡。也使得加密者（來源端）和解密者（目的端）的使用顯示器色域可能差異愈來愈大，為了確保來源端與目的地之間的精準訊息通訊面向而言，代表著這些廣色域顯示器特徵化更顯得重要，也是需要考慮色彩管理的原因。
本篇論文使用ProfileMaker 5.0來製作顯示器的色彩特徵檔，並且驗證於兩台薄膜電晶體液晶螢幕色彩的一致性。之後，使用擴散誤差法來針對三原色的每一通道進行視覺密碼加密處理，也將加密影像減少至兩張影像來隱藏資訊，並可以更簡單來重建影像。結果顯示本方法可以正確讓色彩資訊再現以及分享圖像精確的傳遞。本文也提出了一種應用立體偏光顯示器的新式視覺密碼機制，可對解密影像作準確地立體影像重現。對於立體秘密影像，此方法只使用兩張加密分享影像，並利用影像交錯排列達到解密目標。最後，採用左右影像的像素移動產生像差，探討人眼看見解密後立體影像深度的結果。
利用立體偏光螢幕，對於經過位移左右影像的畫素的主觀實驗中，結果顯示在不同的對比下，位移2到7個影像畫素，可看到解密影像的資訊。對於英文字母的字體在不同的對比下，建議需要50點的大小；而對於數字的字體在不同的對比中建議，需要45點的大小。本研究貢獻於提供了兩種視覺密碼演算法來提升解密影像的品質。第一個方法為將兩種不同類型的螢幕使用色彩管理來正確的傳遞色彩資訊。第二個方法是針對立體顯示器能正確的解密隱藏灰階影像。

Visual cryptography (VC) is a cryptographic scheme which can encrypt the visual information and decrypt the information by human visual system. Color Management is an important issue when display now is one of the most user interface devices in the VC applications. It should be considered about color characterization models between different displays to accurately reproduce decrypted color images. Color gamut is one of characteristics of the color reproduction media for reproducing color images. And many wide color gamut displays are shipping in the markets. It is possible that people use displays with different color gamut in encryption or decryption processes. Therefore, Color Management plays a major role in determining how a given secret image will perform in Visual Cryptography Scheme (VCS).
This study used ProfileMaker 5.0 to create and evaluate the color characterization profiles for two TFT-LCD monitors. And then we applied the algorithm of error diffusion dithering on the primary color channels directly. Results revealed that this method accurately delivered color information and secret image as well. This paper also proposed a new visual cryptography scheme with the stereoscopic display which showed and accurately decrypted the hidden information for stereo gray images. The decryption can be performed via a side-by-side file format of 3D displays. Moreover, results indicated that contrast ratio and pixel disparity of the decrypted stereo-image were key problems that would impact on the perceived quality of the decrypted image.
This research performed a subjective experiment of shifting pixels between both of left and right images to investigate the disparity effects of decrypted information on a film-pattern-retarder display. Results revealed that the disparity thresholds of disparity range have between 2 and 7 pixels in the different contrast ratio. For the size of alphabets, the visible font size was 50 points at least in the different contrast ratio. For number character, the font size was needed 45 points upward in the different contrast ratio.

中文摘要 ................................................I
Abstract ............................................... II
Acknowledgements ....................................... IV
Table of Contents ...................................... V
List of Figures ........................................ VII
Chapter 1 Introduction ..................................1
1.1 Background ......................................... 1
1.2 Motivation ......................................... 1
1.3 Objective .......................................... 2
Chapter 2 Literature Review ............................ 4
2.1 Traditional visual cryptography ........... .........4
2.1.1 Basic visual cryptography .........................4
2.1.2 Extended visual cryptography ..................... 7
2.1.3 Quality evaluation ................................8
2.2 Grayscale and color visual cryptography .............9
2.2.1 Grayscale visual cryptography .....................9
2.2.2 Halftoning ........................................9
2.2.3 Error diffusion ...................................10
2.2.4 Color visual cryptography .........................11
2.3 Visual Cryptography Applications ....................13
2.3.1 Securing display application ......................13
2.3.2 Display characterization for color VC .............14
2.4 Color management (Display characterization)......... 14
2.4.1 International Color Consortium (ICC) ..............14
2.4.2 ICC profile .......................................15
2.4.3 Electro-Optical Transfer Function (EOTF) ..........18
2.5 Stereoscopic display for VC .........................19
Chapter 3 Methodology ...................................22
3.1 Experimental Design .................................22
3.1.1 Display characterization ..........................22
3.1.2 Color visual cryptography .........................24
3.1.3 Stereoscopic visual cryptography for gray images . 28
Chapter 4 Results and Discussion ........................35
4.1.1 ICC profile accuracy ............................. 35
4.2 Color visual cryptography .......................... 40
4.3 Stereoscopic visual cryptography for gray image .....43
4.3.1 Encrypted image simulation ........................43
4.3.2 Decrypted image simulation of LG&reg; monitor .........45
4.3.3 Disparity threshold ...............................48
4.3.4 Relationship between contrast ratio and font size .50
Chapter 5 Conclusions ...................................51
References ............................................. 53
Appendices ............................................. 56
Appendix I: LCD Monitor Reference 2.0.txt................57
Appendix II: 32 Color RGB patches .......................61
Appendix III: Experimental Data .........................63

                                

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