Variable-direction grayscale progressive visual cryptography through share reconstruction
Grayscale visual cryptography based on binary pattern combinations can reconstruct grayscale images without computation but fails to fully utilize binary pixel matrices and generates a large number of shares.Multi-grayscale directional visual cryptography,on the other hand,faces pixel reconstruction conflicts,is complex to construct,and lacks flexibility and universality.To address these issues,a directional grayscale progressive visual cryptography scheme based on share re-construction is proposed.The grayscale secret image is first converted into reduced-grayscale images through multi-level halftoning,which are then directly mapped to binary images.Using a(2,2)threshold visual cryptography scheme,public shares and intermediate shares for hiding different secret images are constructed.By employing a primary-auxiliary diagonal merging method,fused shares are generated,and a transparent pixel-splitting strategy enables progressive reconstruction of different secret images.Theoretical and experimental results demonstrate that compared to binary pattern combination schemes,the proposed method improves visual quality by fully utilizing binary pixel matrices while avoiding excessive share splitting.Compared to directional visual cryptography,the proposed scheme is simpler,more flexible,supports reconstruc-tion in different directions and progressive reconstruction,and maintains good grayscale visual quality.The hidden image can only be reconstructed in the correct overlay direction.
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