Improving Multi-pixel Visual Quality of Invariant Visual Cryptography Scheme

A visual cryptography scheme (VCS) splits the secret image into several shares. Stacking a certain number of shares will reveal the secret image. The principle algorithm (deterministic algorithm) retains the size of shares, and the revealed image is at least double the size of the secret image with good visual quality. In contrast, the probabilistic algorithm has the size of the revealed image equal to that of the secret image with the noisily revealed image. Multi-pixel algorithm cast solutions for the trade off problems between the good visual quality and the non-expansion size of the revealed image. In this paper, we introduce new algorithms for multi-pixel to improve the quality of preceding algorithms, generalize the multi-pixel algorithm, provide evidence of the best form of multi-pixel, and contribute to the thin line problem.