Extended Visual Cryptography for Photograph Images - Visual Cryptography and Secret Image Sharing - page 108

TABLE 4.2
Approaches to photograph visual cryptography of (2; 2) scheme. "pair" repre-
sents constraints on a pair of shadow images such as random-dot binary image
("rand."), similar images ("sim."), positive/negative pair ("p/n"), and dier-
ent pair, i.e., no constraint ("di."). "tone" indicates types of images to be
reconstructed. "logo" stands for a logo-like image, "logo tr." stands for a logo-
like image with traces of shadows, and "gray" stands for a gray-scale image.
"GAS," "RG," "not ext.," and "cont. tone" mean General Access Structure,
Random Grids, not extended, and continuous-tone, respectively.

shadow image secret image

approaches m features

pair S l S tone R l R

[4, 15] >1 rand. 0 1 gray 1=2 <m GAS, not ext.

[37] 1 rand. 0 1 gray 1=2 >2 RG, not ext.

[14, 6] 1 rand. 0 1 gray 1=2 >2 (k;n), not ext.

[33] >1 sim. ' 1 m+1 logo tr. 0 density pattern

[34, 21, 41] 1 sim. ' 1 >2 logo tr. 0 ordered dither

[9] 1 sim. ' 1 >2 logo tr. 0 error diusion

[47] 1 & 4 p/n 1=2 >2 logo 1=4 2 GAS, w/o trace

[10] 1 di. 1 >2 logo tr. 0 error diusion

[45] 4 diff. 1=4 1 logo tr. 1=4 GAS, cont. tone

[28] >1 di. 1=4 <m gray 1=4 <m density pattern

[42] 1 di. 1=4 >2 gray 1=4 >2 iterative search

[25, 26] 1 di. 1=4 >2 gray 1=4 >2 error diffusion

[29] 2 di. 1=4 1 gray 1=4 1 cont. tone