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 A new visual cryptography with multi-level encoding

Cheng-Chi Lee (2014) Visual Secret Sharing (VSS) is a visual cryptography scheme which decodes secret messages into several enlarged shares and distributes them to different participants. The participants can recover the secret messages by stacking their shares, and then secret message can be revealed by human visual sensitivity. Afterward some researchers start to research size invariant scheme and apply to encode grayscale images such as scenic photos or pictures, not only binary messages. Owing to the gray values distribution of pictures are different, extreme distribution may cause blurred revealed image. proposed a size invariant VSS scheme which is suitable for different distribution of image gray values. Experiment results show that the reconstructed images of our method, for brighter, darker, and normal images, have clearer and higher contrast, and without apparent artefact and unexpected contour. In particular, the important spectral property of the target image is not considered in the design and evaluation of VC algorithms.