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Proceedings Paper

Registration-tolerant extended visual cryptography
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Paper Abstract

Extended Visual Cryptography is a method which encodes a number of images so that when the images are superimposed, the hidden image appears without a trace of original images. The decryption is done directly by human eyes without cryptographic calculations. The proposing system takes three pictures as input and generates two images which correspond to two of the input pictures. The third picture is perceived by superimposing the two output images. Previous methods are based on halftoning and Boolean operations. Transparency values must be quantized before encryption, and a pixel is halftoned by a fixed numbers of completely transparent and opaque subpixels. Then a transparency of the superimposed pixel is controlled by changing the subpixel arrangements of the two output pixels. Since the subpixel arrangement is basically random, a tradeoff exists that to express the more graylevels, each subpixel must become the smaller, making it the more difficult to superimpose by hand. Our new approach tolerates registration error for the third image and eases the difficulty, by adopting concentric-circular subpixel arrangement and continuous grayscale subpixel values. The system becomes considerably robust to the registration error. Also, it achieves quality improvement for all three images, by explicitly dealing with continuous graylevels.

Paper Details

Date Published: 17 June 2003
PDF: 12 pages
Proc. SPIE 5007, Human Vision and Electronic Imaging VIII, (17 June 2003); doi: 10.1117/12.473920
Show Author Affiliations
Mizuho Nakajima, Univ. of Tokyo (Japan)
Yasushi Yamaguchi, Univ. of Tokyo (Japan)

Published in SPIE Proceedings Vol. 5007:
Human Vision and Electronic Imaging VIII
Bernice E. Rogowitz; Thrasyvoulos N. Pappas, Editor(s)

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