Threshold visual secret sharing by random grids with improved contrast

Improved Contrast for Threshold Random-grid-based Visual Cryptography

“…Secondly, considering that the visual quality of the recovered images is evaluated by contrast in Definition 1, we further give the quantitative contrast comparisons. Note that only Chen and Tsao [22], Wu and Sun [34] and ours give the theoretical contrast while Guo et al [33], Shyu [35] and Yan et al [36] do not provide. And the contrasts in Guo et al [33], Shyu [35] and Yan et al [36] are obtained by experiments.…”

“…In this section, we mainly focus on our advantages in contrast improvement, and other common good features such as no codebook design and no pixel expansion are not discussed again here. Firstly, we give the visual quality comparisons of illustrations among ours and related schemes especially Chen and Tsao [22], Guo et al [33], Wu and Sun [34]. Secondly, considering that the visual quality of the recovered images is evaluated by contrast in Definition 1, we further give the quantitative contrast comparisons.…”

“…At present, several algorithms [22,[33][34][35][36] for (k, n) RG-based VCS were proposed. Herein, we review and analyze some classical related schemes especially Chen et al [22], Guo et al [33], Wu and Sun [34], which are presented as Algorithm 1, Algorithm 2, and Algorithm 3, respectively. Algorithm 1 [22] Input: A binary secret image S, whose size is M×N.…”

“…Since then, many interesting schemes were proposed in recent years i.e. Guo et al [33], Wu and Sun [34], Shyu [35] and Yan et al [36] to improve the first scheme by Chen and Tsao [22]. They all focused on the threshold RG-based VCS, regarded as the basis for GAS-VCS and other applications.…”

“…where ⊕ is the Boolean XOR operation. Then Guo et al [33] improved the contrast in another approach. They repeat the (k, k)-VCS / n k     times to generate the first / k n k ⋅     pixels and assign the last / n k n k − ⋅    pixels randomly.…”