A Visual Cryptographic Technicque for Chromatic Images Using Multi-Pixel Encoding Method.

Journal of Research and Practice in Information Technology (Impact Factor: 0.22). 01/2005; 37(2).
Source: DBLP


Visual cryptography is a secret sharing method that uses human eyes to decrypt the secret. Most visual cryptographic methods utilize the technique of pixel expansion, which causes the size of the shares to be much larger than that of the secret image. This situation is more serious for grey-level and chromatic images. In this paper, we propose a multi-pixel encoding method for grey-level and chromatic images without pixel expansion. We simultaneously encrypt r successive white or black pixels each time. The probability of these r pixels being coloured black depends on the ratio of blacks in the basis matrices. Afterward, we incorporate the techniques of colour decomposition and halftoning into the proposed scheme to handle grey-level and chromatic images. The experimental results show that the shares are not only the same size as the secret image, but also attain the requirement of security. The stacked images have good visual effect as well. Besides, our method can be easily extended to general access structure.

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    • "Gray 1 k=n=2 2 levels × HT [23] √ 1 √ 2 levels × "
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    ABSTRACT: A k-out-of-n Extended Visual Cryptography Scheme (EVCS) is a secret sharing scheme which hides a secret image into n shares, which are also some images. The secret image can be recovered if at least k of the shares are superimposed, while nothing can be obtained if less than k shares are known. Previous EVCS schemes are either for black-and-white images or having pixel expansion. In this paper, we propose the first k-out-of-n EVCS for color images with no pixel expansion. The scheme also improves the contrast of the n shares and the reconstructed secret image (i.e. the superimposed image of any k or more shares) by allowing users to specify the level of each primary color (i.e. Red, Green and Blue) in the image shares as well as the reconstructed secret image.
    SECRYPT 2010 - Proceedings of the International Conference on Security and Cryptography, Athens, Greece, July 26-28, 2010, SECRYPT is part of ICETE - The International Joint Conference on e-Business and Telecommunications; 01/2010
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    • "So the encoding efficiency is promoted largely. The idea of encoding block by block is also called multi-pixel encoding method by Hou and Tu in [10] [11] "
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    ABSTRACT: In visual secret sharing (VSS) schemes, a secret image can be visually revealed from overlapping shadow images without additional computations. However, the contrast of reconstructed image is much lost. Employing reversing operation to reverse black and white pixels as well as increasing encoding runs is an effective way to improve the contrast. A novel VSS scheme with reversing is presented in this paper. It achieves really ideal contrast within only [m/h] encoding runs (where m and h are the number of the total columns and the number of the wholewhite columns in the basis matrix to encode white pixels, respectively) and no pixel expansion occurs. It encodes the secret image block by block. A block consists of m pixels, which means that m pixels together join into each encoding step. It is suitable for all access structures and can be applied to encrypt black-white, gray-scale and chromatic images. The experimental results, analyses and comparisons show that the proposed scheme is optimal among those schemes with reversing in encoding runs, pixel expansion, complexity, system capacity and encoding efficiency.
    Journal of multimedia 06/2009; 4(3). DOI:10.4304/jmm.4.3.104-111
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    • "Despite the improvement for encoding efficiency, this scheme exhibits poor quality of stacked image for most access structures other than (2, 2) threshold access structure. Afterwards, they proposed another multi-pixel encoding method in [17] to win an improvement for the quality of revealed image. This scheme also encodes m pixels at each run nevertheless the m pixels are of same type. "
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    ABSTRACT: 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.
    Journal of Computers 12/2008; 3(12). DOI:10.4304/jcp.3.12.68-75
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