Ramp secret image sharing

Secret image sharing (SIS) belongs to but differs from secret sharing. In general, conventional (k,n) threshold SIS has the shortcoming of "all-or-nothing". In this article, first we introduce ramp SIS definition. Then we propose a (k₁,k₂,n) ramp SIS based on the Chinese remainder theorem (CRT). In the proposed scheme, on the one hand, when we collect any k₁ or more and less than k₂ shadows, the secret image will be disclosed in a progressive way. On the other hand, when we collect any k₂ or more shadows, the secret image will be disclosed losslessly. Furthermore, the disclosing method is only modular arithmetic, which can be used in some real-time applications. We give theoretical analyses and experiments to show the effectiveness of the proposed scheme.