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TopShamir secret sharing scheme of Galois is used to generate protected shares and reduce the pixel expansion problem. Chang-Chou and Wen-Hsiang introduce a (2, 3)-threshold visual secret sharing technique in 2003 where secret image was reconstructed by gathering any two of the three shares. Good experimental results prove that this technique is suitable for mobile and handheld devices applications (Lin and Tsai, 2003). (Adel, 2005) present a watermarking system based on visual secret sharing approach. (Kun-Yuan and Ja-Chen, 2006) present a (2, 3)-threshold visual secret sharing system for color images. The system converts the input image into Cyan Magenta Yellow (CMY) color model. Each layer of CMY is transformed from 8-bit to 1-bit by halftone algorithm which is either 0 or 1. The visual secret sharing is achieved by another method which differs from Naor-Shamir method. The experimental results explain the limitation according to the large pixel expansion and bad image quality or contrast.
(Chin-Pan and Ching-Chung, 2007) propose a (4, 6)-threshold secret image sharing method using integer wavelet transform and Shamir secret sharing scheme of Galois filed. This method processes the transformed coefficients in each sub-band to be combined with each other and divides each of the resulting combination coefficients into number of shares. The experimental results show that this method yields small shares and it is suitable for online applications and perfect reconstruction of secret image.
At the same time, the individual protected shares do not reveal the identity of the original image (Arun and Asem, 2010). The results confirm that private face image is camouflaged to two secured shares and the face image is matched successfully.