Visual Cryptography and Secret Image Sharing

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

4.2 Basic Visual Cryptography Schemes

4.2.1 (k, n) Visual Secret Sharing Schemes

4.2.2 Extended Visual Cryptography Scheme

4.2.3 Random Grids

4.3 Fundamentals of Photograph Visual Cryptography

4.3.1 Digital Halftoning

Density Pattern

Noise-Encoding

Ordered Dither

Error Diffusion

Iterative and Search-Based Methods

4.3.2 Image Quality and Related Parameters

4.3.3 Photograph Visual Cryptography with Basic Schemes

4.4 Variations of Photograph Visual Cryptography

4.4.1 Approaches to Photograph Visual Cryptography

4.4.2 Random-Dot Shadow Images

4.4.3 Similar Shadow ...