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標題: A multiple-level visual secret-sharing scheme without image size expansion
作者: Chen, Y.F.
Chan, Y.K.
Huang, C.C.
Tsai, M.H.
Chu, Y.P.
關鍵字: visual cryptography;visual secret sharing (VSS);image security;halftone image;color images;cryptography;encryption
Project: Information Sciences
期刊/報告no:: Information Sciences, Volume 177, Issue 21, Page(s) 4696-4710.
In traditional VSS schemes, the size of the share image is substantially expanded since each pixel of the secret image is mapped onto a block consisting of several pixels. In addition, the quality of the reconstructed secret image is normally degraded in contrast, especially for halftone images. This study proposes a VSS scheme that maps a block in a secret image onto one corresponding equal-sized block in each share image without image size expansion. Two types of techniques, including histogram width-equalization and histogram depth-equalization, are proposed to generate the corresponding share blocks containing multiple levels rather than two levels based on the density of black pixels on the blocks for a secret block. In the former technique, the gray-scale image histogram is obtained by uniformly splitting the range of the pixel gray levels in the secret image, while in the latter the buckets are created so that the area of each bucket is roughly constant by containing approximately the same number of pixels. The proposed schemes significantly improve the quality of the reconstructed secret image compared to several previous investigations. (c) 2007 Elsevier Inc. All rights reserved.
ISSN: 0020-0255
DOI: 10.1016/j.ins.2007.05.011
Appears in Collections:資訊管理學系

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