10-02-2017, 10:02 AM
It is now common to transfer multimedia data over the Internet. It is necessary to solve the problem of ensuring the security of information in the increasingly open network environment of today. Traditional cryptography encryption technologies are generally used to protect the security of information. With these technologies, the data becomes disordered after being encrypted and then can be retrieved by a correct key. Without the correct key, the contents of the encrypted source can not be detected even if unauthorized persons steal the data. Naor and Shamir proposed a new area of cryptography, visual cryptography , in 1994. The most notable feature of this approach is that it exploits the human visual system to read the secret message of some overlapping actions, thus overcoming the disadvantage of complex Computing required in traditional cryptography. The threshold scheme makes the application of visual cryptography more flexible. In a k-out-of-n scheme of VC, a secret binary image is cryptographically encoded in n parts of random binary patterns. The n actions are xeroxed in n transparencies, respectively, and distributed among n participants, one for each participant. No participant knows the part given to another participant. Any k or more participants can visually reveal the secret image by superimposing any k transparencies together. The secret can not be decoded by any k-1 or less participants, even if infinite computational power is available to them. Apart from the obvious applications of information hiding, there are many VC applications, which include general access structures, copyright protection, watermarks, visual authentication and identification, print and scan applications, and so on. Many studies of visual cryptography have been published. Most of them, however, have concentrated on discussing black and white images, and only a few of them have proposed methods for processing gray and color images. There is a general method for VC scheme based on general access structure. The access structure is a specification of qualified and prohibited subsets of actions. Participants in a qualified subset can retrieve the secret image while participants in a prohibited subset can not. The concept of VC scheme has been extended to shared images in grayscale instead of sharing binary images. Although the secret image is grayscale, the parts are still constructed by random binary patterns that carry visual information that can lead to the suspicion of secret encryption. The concept of extended visual cryptography (EVC) is developed in which actions contain not only the secret information, but are also meaningful images. Hypergraphic colors are used in building meaningful images using randomly distributed pixels, resulting binary actions contain strong white noise that leads to inadequate results. This document introduces a VC color coding method to generate meaningful actions. It is based on two fundamental concepts used in the generation of actions that are the diffusion of errors and the synchronization of pixels. The diffusion of errors is a procedure that produces pleasant images of semitones to the human vision. The synchronization of the pixels of the secret image and the coverage images through the color channels improves the visual quality of the actions. Visual information Pixel synchronization (VIP) prevents the colors and contrast of the original parts from being degraded even with the permutation of the matrix and also maintains the position of the pixels in all channels.