Visual cryptography for multi-color LCD projectors

Abstract

Visual Cryptography was introduced by Naor and Shamir in 1998. Advantages of visual cryptography are that no decrypting computation and key are needed so that researchers can concentrate on enhancing visual cryptography. Visual cryptography was modified from encrypting binary images to grey-level images. Although the amount of information contained has been raised a lot, the control of contrast loss is still kept more or less the same throughout these years. Besides that, the use of LCD projectors for encrypted shares presentation was proposed in 2003. Alignment becomes an obvious problem since images projected are more difficult to align than traditional presenting medium -transparencies. This project proposes to develop an application, which proves that the concept of Young-Chang HOU can work on visual cryptography for colour images. Alignment function for LCD projectors is also one of the main features in this application. In this application, colour image is encrypted based on the principle of visual cryptography to achieve perfect security level. LCD projectors are used for projecting encrypted colour images so that contrast loss is reduced to an appreciated level. Alignment function provides a convenient environment such that users do not need to adjust the encrypted images again once they see the original image. Finally, decryption is still handled by human visual system without computation, which is the basic principal of visual cryptography.