Two-Decoding-Option Image Sharing Method - Visual Cryptography and Secret Image Sharing - page 458

Example 1. Construct a (2, 2)-VCS of h = 1, l = 0, and m = 2 using

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01

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B 1 = and B 0 = . The secret is a printed-text image VCS .

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01

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has H (OR (B 1 j2)) = 2,
H (OR (B 0 j2)) = 1, and H (OR (B 1 j1)) = H (OR (B 0 j1)) = 1, which satisfy
(V-1) and (V-2) conditions. In the reconstructed image, the black color is
2B0W and the white color is 1B1W (or 1W1B). However, each shadow con-
tains 1B1W and 1W1B with the same frequencies so that one cannot see
anythi ng fro m his own shadow. Figure 17.1(a) is a black-and-white secret
image VCS . Two noise-like shadows (Shadow 1, Shadow 2) and the recon-
structed image by stacking two shadows (Shadow 1 + Shadow 2) are shown
in Figures 17.1(b), 17.1(c) and 17.1(d). The printed-text secret

A (2, 2)-VCS with B 1 = and B 0 =

VCS can be

revealed by HVS.

2

(a) (b) Shadow 1 (c) Shadow 2

(d) Shadow 1+Shadow 2

FIGURE 17.1
A (2, 2)-VCS of h = 1;l = 0, and m = 2: (a) the secret image (b) and (c) two
shadows (d) the reconstructed image.