Visual Cryptography in reversible style

1. Visual Cryptography in reversible style Wen Pinn Fang Computer Science and Information Engineering Department Yuanpei University wpfang@mail.ypu.edu.tw Reporter:赵旻玥 May, 6, 2008

2. 1 Introduction TheGoal Analysis Design Fig.1 Some sharing blocks. Notation and Definition: Experiment 256blocks: 1≤x ≤256, 1≤y ≤256. S1 and S2: the two generated transparencies. (x,y): the 3-by-3 block at location (x,y) of each transparency. B: a black block. W: a white block. Summary 3-by-3 block: 8 black elements, 1 white element. 3-by-3 block: 6 black elements, 3 white elements.

3. 2 The Goal The Goal Analysis Design Experiment Summary Fig.2 Visual Cryptography in reversible style.

4. 3 The local detail about stacking the two transparencies The rules to design the transparencies: The Goal Analysis Design Experiment Summary the symbol “E”􀆎 becomes 􀆎􀆎􀆎 􀀇 􀆎 Fig.3 Two types of stacking.

5. 4 The design of the two transparencies S1 and S2 The Goal Analysis Design Experiment Summary Fig.5 Three kinds of perturbation operation to get some other combinations of pattern blocks whose stacked results are all (W,W,W,W). Fig.4 the pattern blocks {α1,β1, α2,β2} used in our method to paint the two transparencies.

6. 5 Experiment Result The two generated transparencies. The Goal Analysis Design Experiment The two original images. Summary {(c),(d)} {(d)turn-over,(c)} The two recovered images.

7. 6 Summary and Future Works The major contributions: 1) the back-view of one the two transparencies was also used, 2) more than one secret image is shared using two noisy transparencies (S1 and S2). The Goal Analysis Design In the future: 1) discuss how to design two non-noisy transparencies, 2) try to find more methods to perturb the patterns in Figures 6 to deal with the contour problem in the transparencies, and reduce the left-to-right discontinuity behavior of the patterns across the vertical middle line {(x,y)| x=128 and y=1,2,…,256)} in the stacked results. Experiment Summary