Summary: | Secret image sharing (SIS) belongs to but differs from secret sharing. In general, conventional (<i>k</i>, <i>n</i>) threshold SIS has the shortcoming of pall-or-nothingq. In this article, first we introduce ramp SIS definition. Then we propose a $(k_1, k_2, n)$ ramp SIS based on the Chinese remainder theorem (CRT). In the proposed scheme, on the one hand, when we collect any $k_1$ or more and less than $k_2$ shadows, the secret image will be disclosed in a progressive way. On the other hand, when we collect any $k_2$ 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.
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