Multi-tone meaningful visual cryptography scheme based on optical axis angle superposition

Abstract

The visual cryptography scheme based on polarization uses the polarization state of light to encrypt images, ensuring that the share images have no pixel expansion and that the secret image can be reconstructed without loss of quality. However, its shares are meaningless noise images. To solve this problem, a multi-tone meaningful visual cryptography scheme based on optical axis angle superposition (OAAS-MVC) is proposed. In our scheme, both secret images and cover images are multi-tone images. In the encoding phase, the image’s pixel is converted into the optical axis angles of the retarder film component (RFC). By adjusting the angles of the $n$ $\lambda$/2 RFCs to specific angles, they can represent the pixel of the cover image. The share images are generated as meaningful images with the appearance of cover images. In the decoding phase, the angles of the $n$ $\lambda$/2 RFCs are superimposed to reconstruct the secret image. Compared to other classic meaningful visual cryptography schemes, our scheme significantly improves the quality of the shares and the reconstructed secret image. The experimental results demonstrated the effectiveness and security of the scheme.