ISSN : 1796-203X
Volume : 3    Issue : 12    Date : December 2008

Visual Cryptography for General Access Structure Using Pixel-block Aware Encoding
Haibo Zhang, Xiaofei Wang, Wanhua Cao, and Youpeng Huang
Page(s): 68-75
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Multi-pixel encoding is an emerging method in visual cryptography for that it can encode more than
one pixel for each encoding run. Nevertheless, in fact its encoding efficiency is still low because of
that the encoding length is invariable and very small for each run. This paper presents a novel
multi-pixel encoding called pixel-block aware encoding. It scans the secret image by zigzag and
perceives a pixel block with as many pixels as possible to encode for each run. A pixel-block
consists of consecutive pixels of same type during the scanning. The proposed scheme has
advantage in encoding efficiency over singlepixel encoding and other known multi-pixel encoding
methods. Furthermore, this scheme can work well for both threshold access structure and general
access structure and well for both gray-scale and chromatic images without pixel expansion. The
experimental results also show that it can achieve good quality for overlapped images.

Index Terms
Visual secret sharing (VSS), general access structure, multi-pixel encoding, pixel-block aware
encoding, zigzag scanning