Cryptography Reference
In-Depth Information
4
Extended Visual Cryptography for
Photograph
Images
Yasushi Yamaguchi
The University of Tokyo, Japan
Japan Science and Technology Agency / CREST, Japan
CONTENTS
4.1
Introduction ::::::::::::::::::::::::::::::::::::::::::::::::::::::
96
4.2
Basic Visual Cryptography Schemes :::::::::::::::::::::::::::::
96
4.2.1
(k;n) Visual Secret Sharing Schemes :::::::::::::::::::
96
4.2.2
Extended Visual Cryptography Scheme :::::::::::::::::
99
4.2.3
Random Grids ::::::::::::::::::::::::::::::::::::::::::: 101
4.3
Fundamentals of Photograph Visual Cryptography ::::::::::::: 103
4.3.2
Image Quality and Related Parameters ::::::::::::::::: 106
4.3.3
Photograph Visual Cryptography with Basic Schemes : 107
4.4
Variations of Photograph Visual Cryptography ::::::::::::::::: 109
4.4.1
Approaches to Photograph Visual Cryptography ::::::: 109
4.4.2
Random-Dot Shadow Images :::::::::::::::::::::::::::: 111
4.4.3
Similar Shadow Images :::::::::::::::::::::::::::::::::: 111
4.4.4
Positive and Negative Shadow Images :::::::::::::::::: 112
4.4.5
Error and Secret Diusion ::::::::::::::::::::::::::::::: 113
4.4.6
Simultaneous Iterative Search ::::::::::::::::::::::::::: 114
4.4.7
Tone Adjustment :::::::::::::::::::::::::::::::::::::::: 114
4.4.8
Continuous-Tone Subpixel ::::::::::::::::::::::::::::::: 115
4.5
Misalignment-Tolerant Photograph Visual Cryptography ::::::: 116
4.5.1
Theory and Implementation ::::::::::::::::::::::::::::: 116
4.5.2
Results ::::::::::::::::::::::::::::::::::::::::::::::::::: 120
4.6
Conclusions ::::::::::::::::::::::::::::::::::::::::::::::::::::::: 120
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