k out of n Region Incrementing Scheme in Visual Cryptography

• Main Authors: Hsiang-Wen Shih, 石翔文
• Other Authors: Ching-Nung Yang
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/41060302569445021151

碩士 === 國立東華大學 === 資訊工程學系 === 100 === In a (k, n) visual cryptography scheme (VCS), a secret image is encoded into n shadow images that distributed to n participants. Any k participants can reveal the secret image by stacking their shadow images to visually decode the secret image without the help of hardware or computation, but (k1) or fewer participants will not gain any information. The beautiful property of VCS is the ease of decoding, the stacking-to-see property, and it can be adopted in many applications such as digital image indexing, watermarking, securing display, embedding private information. Recently, Wang introduced a novel (2, n) region incrementing visual cryptographic scheme, which can gradually reconstruct secrets in a single image with multiple security levels. In RIVCS, a secret image is subdivided into multiple regions in such way that any t shadow images, where 2tn, can be used to reveal the (t1)-th region. However, Wang’s scheme suffers from the incorrect-color problem, which the colors of reconstructed images may be reversed (i.e., the black and white are reversed). If the color of text is also the secret information, the incorrect-color problem will compromise the secret. Additionally, Wang's scheme is only suitable for the 2-out-of-n case, i.e., (k, n)-RIVCS where k=2. In this thesis, we propose the general (k, n)-RIVCS revealing the correct colors for all regions, where k and n can be any integers. We also propose the modified (k, n)-RIVCS to enhance the contrast and reduce the size of shadow image compared with Wang’s scheme, where k and n can be any integers. Finally, we theoretically prove that the proposed (k, n)-RIVCS satisfies the security and contrast conditions.