Threshold construction from specific cases in visual cryptography without the pixel expansion

Unexpanded shares can decrease the bandwidth and save storage in a visual cryptography scheme (VCS). To avoid the pixel expansion, some previous VCSs without the pixel expansion were given. However, most of them are only for specific cases other than general threshold (case). In this paper, three general threshold construction methods from specific cases are proposed. The constructed threshold VCSs are also progressive VCS without the pixel expansion. Analyses and experiments are conducted to evaluate the security and efficiency of the proposed methods.