An improved grayscale visual secret sharing scheme for visual information security

In the last few years, with increasing popularity of the visual communications technology, also the interest in robbing the secret information has risen. The field of information security has an important issue even in the field of medical imagery. Visual Cryptography (VC) is a revolutionary encryption methodology to share the image secret information in a secure way. This paper considers the problem of encoding a secret gray scale image GI into n shares of meaningful halftone images within the scheme of visual cryptography. We provide an overview of the emerging Visual Cryptography (VC) techniques used in the secure transfer of the thousands of images collected and stored in medical imagery system. In this paper, we propose a (2,2) improved gray scale visual secret sharing (IGVSS) scheme using dynamic threshold method to reduce the problems of computational complexity and pixel expansion. The proposed IGVSS scheme, to encode the secret information into meaningful shares for producing high quality share images. For encoding the secret information, VC is demonstrated in two levels. In first level, single Meaningful Visual Image (MVI) is used to generate multiple shares. In second level, two meaningful visual images are employed to generate multiple shares. It is hard to perceive any clues about a secret image from individual shares. The experimental result ensures the security and quality of the reconstructed secret images.