| Summary: | 碩士 === 大同大學 === 電機工程學系(所) === 97 === In the field of information security, there is a category of technology called Information Hiding Technique [1] which encrypts and decrypts in different ways from the traditional encryption technology in the past. It is based on the behavior of hiding secret information , thus ensure the security.
One of the Information Hiding Techniques, called Visual Cryptography proposed by [3] Noar and Shamir in 1994, does not need computer calculation because it has no complicated calculation formula. We can decode the hidden information by color contrast and superimposing shares which consist of a transparency through human visual system.
In the original Visual Cryptography, the pixels of the image are almost composed of black and white. Consequently, whether in the cover images of separated shares or images reconstructed by superimposing shares, the color performance is restricted to black and white. As a result, color visual cryptography was then developed. Adding colors makes images more vivid and closer to people’s life.
It is found that not every coding manner can precisely depict the original colors of encrypted or reconstructed images. In [2] it proposed a good algorithm to share a secret gray image in Multiple images. However, the outcome of camouflage image is not satisfactory, and the picture is also enlarged to 3×3, which is 9 times bigger than the original image size. This thesis is to improve this algorithm to make the camouflage images more similar to the original cover images, and reduce the size enlarged from 3×3 to 2×2, so as to decrease the zoom ratio.
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