Let $G=(V,E)$ be a connected graph and $\Gamma (G)$ be the strong access structure where obtained from graph $G$. A visual cryptography scheme (VCS) for a set $P$ of participants is a method to encode a secret image such that any pixel of this image change to $m$ subpixels and only qualified sets can recover the secret image by stacking their shares. The value of $m$ is called the pixel expansion and the minimum value of the pixel expansion of a VCS for $\Gamma (G)$ is denoted by $m^{*}(G)$. In this paper we obtain a characterization of all connected graphs $G$ with $m^{*}(G)=4$ and $\omega (G)=5$ which $\omega(G)$ is the clique number of graph $G$.
Davarzani, M. (2019). Visual cryptography scheme on graphs with $m^{*}(G)=4$. Transactions on Combinatorics, 8(2), 53-66. doi: 10.22108/toc.2019.113671.1599
MLA
Mahmood Davarzani. "Visual cryptography scheme on graphs with $m^{*}(G)=4$". Transactions on Combinatorics, 8, 2, 2019, 53-66. doi: 10.22108/toc.2019.113671.1599
HARVARD
Davarzani, M. (2019). 'Visual cryptography scheme on graphs with $m^{*}(G)=4$', Transactions on Combinatorics, 8(2), pp. 53-66. doi: 10.22108/toc.2019.113671.1599
VANCOUVER
Davarzani, M. Visual cryptography scheme on graphs with $m^{*}(G)=4$. Transactions on Combinatorics, 2019; 8(2): 53-66. doi: 10.22108/toc.2019.113671.1599
)