Color transfer in visual cryptography

Visual cryptography is an important technique for image encryption. This paper proposes a color transfer scheme which can be incorporated into the (k, n) visual cryptography model. In encoder, a color image is encrypted into n noise-like binary share images. When any k or more than k shares are collected, a high quality colorful version of the secret image can be reconstructed with low complexity computations. The principle is motivated to develop a color image secret sharing for output devices such as monochrome printer or fax machines. The generated share images are still binary transparencies which can be directly produced by these low cost output devices. Meanwhile, the security of a (k, n) visual cryptography model is perfectly preserved. When stacking a qualified set of transparencies, the gray level version of secret content can be revealed by human visual system. Nevertheless, the proposed paradigm is cheating immune. It also can be integrated into some emerging display technologies such as cholesteric liquid crystal display. Experimental results and related examples demonstrate the effectiveness and efficiency.