Contrast-Enhanced Visual Cryptography Schemes Based on Additional Pixel Patterns

Visual cryptography is a kind of secret image sharing scheme that uses the human visual system to perform the decryption computations. A visual cryptography scheme allows confidential messages to be encrypted into k-out-of-n secret sharing schemes. Whenever the number of participants from the group (n) is larger than or equal to the predetermined threshold value (k), the confidential message can be obtained by these participants. Contrast is one of the most important parameters in visual cryptography schemes. Usually, the reconstructed secret image will be darker (through contrast degradation) than the original secret image. The proposed scheme achieves better contrast and reduces the noise in the reconstructed secret image without any computational complexity. In this method, additional pixel patterns are used to improve the contrast of the reconstructed secret image. By using additional pixel patterns for the white pixels, the contrast of the reconstructed secret image can be improved than in the case of existing visual cryptography schemes.