Weighted visual cryptographic scheme with improved image quality

Abstract

The weighted visual cryptographic scheme (WVCS) allows the dealer to assign a weight to every shadow (participant) according to the participant’s importance so that the ability of each shadow to reveal a secret image can be varied. However, the previous weighted random grid-based VCS (WRGVCS) has the shortcoming of low visual quality. The contribution of this paper is that a new WRGVCS for a (k, n) threshold is designed to improve the image quality of the revealed secret image and to realize more features. RG is utilized to achieve the features of no pixel expansion and no codebook design. The probability of covering the valid bits is improved to improve the image quality. Experimental results and security analyses indicate the effectiveness of the designed scheme. Contrast and feature comparisons with previous weighted VCS approaches exhibit improvements in the designed scheme over other relative weighted VCSs. The limitations of our work are that the weighted effect decreases for some thresholds, and the theoretical contrast of the designed scheme is not derived directly by the parameters.