Visual Cryptography and Random Grids - Visual Cryptography and Secret Image Sharing - page 213

of less than four shares tells anything about B. fR 1 ;R 2 ;R 3 ;R 4 g is indeed a
set of VCRG-4.

(a) (b) (c)

(d) (e) (f)

(g) (h)

FIGURE 7.12
Results of Algorithms 4 for VCRG-4 with respect to binary image B: (a) B;
(b) R 1 , (c) R 2 , (d) R 3 , (e) R 4 ; (f) R 1 R 2 ; (g) R 1 R 2 R 3 ; (h) R 1 R 2 ;
(g) R 1 R 2 R 3 R 4 .

Since n = 4 in this experiment, we have T (R i ) = 1=2 (see Figures 7.12(b){

(e)), (R i R j R k ) = 1=8 (see (g)) for

1 6 i 6= j 6= k 6 4. Further, from Table 7.6 we know that the light contrast
of Algorithm 4 is c(

T (R i R j ) = 1=4 (see (f)), and T

E 4 ) = 1=8 for n = 4. Figure 7.13 gives some experimental
results of Algorithm 8 for color VCRG-4 where Eycrypt cVCRG (P x ,x, 4)
was based upon Algorithm 4 with respect to P (see Figure 7.9(a)) . Figures
7.13(a){(d) are the color random gridsR 1 ;R 2 ;R 3 ;R 4 produced; (e) presents
the result ofR 1 R 2 ; (f) shows that ofR 1 R 2 R 3 ; and (g) gives that of
R 1 R 2 R 3 R 4 . As seen from Figure 7.13, we realize that fR 1 R 2
R 3 R 4 g is a set of color VCRG-4 of P.
The results of the above four experiments are visualized evidences to the
correctness of Theorems 2{4. The proposed schemes (Algorithms 4-8) in pro-
ducing VCRG-n for a secret image are feasible and applicable. Among the