Cryptography Reference
In-Depth Information
13
Steganograp hy in Halftone Images
Oscar C. Au
Hong Kong University of Science and Technology, China
Yuanfang Guo
Hong Kong University of Science and Technology, China
John S. Ho
Hong Kong University of Science and Technology, China
CONTENTS
13.1
Introduction :::::::::::::::::::::::::::::::::::::::::::::::::::::: 351
13.2
A Review of Error Diusion ::::::::::::::::::::::::::::::::::::: 352
13.3
Data Hiding by Stochastic Error Diusion (DHSED) ::::::::::: 356
13.4
Data Hiding by Conjugate Error Diusion (DHCED) :::::::::: 359
13.5
Performance Analysis ::::::::::::::::::::::::::::::::::::::::::: 363
13.6
Summary :::::::::::::::::::::::::::::::::::::::::::::::::::::::: 377
Bibliography :::::::::::::::::::::::::::::::::::::::::::::::::::::::: 379
13.1 Introduction
While gray-scale images can be readily displayed in computer monitors and
other light-emitting displays, they also need to be displayed routinely in other
reflective media such as newspaper, magazines, books, and other printed doc-
uments. However, in reflective media, the application of ink on the reflective
media implies that only 1-bit images (with two tones: black and white) can
be displayed. A problem arising from this is that straightforward 1-bit quan-
tization on an image would lose most of the important image details. With
such constraints, there is a class of image processing technique called image
halftoning that converts an 8-bit image into an 1-bit image, which resembles
the 8-bit image when viewed from a distance. Such 1-bit images are called
halftone images [1]. Halftone image technologies are widely used in printed
matters.
There are two main kinds of halftoning methods: ordered dithering [1] and
 
 
 
 
 
 
 
 
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