Equivalence Proof of Two (2, n) Progressive Visual Secret Sharing

Apart from traditional visual secret sharing (VSS), progressive visual secret sharing (PVSS) can gain clearer recovered secret image with more shares. In the literature, Hou and Quan [Hou, Y. C., Quan, Z. Y.: Progressive visual cryptography with unexpanded shares. IEEE Trans. on Circ. and Sys. for Video Tech. 21(11), Pages 1760-1764(2011)], and Chen et al. [Chen, T.-H., et al., Quality-adaptive visual secret sharing by random grids. J. Syst. Software, Volume 86, Issue 5, May 2013, Pages 1267-1274(2013)] proposed two PVSS schemes, respectively, that solved the pixel expansion and poor visual quality problems of previous PVSS. In this paper, we show that the two means are equal in terms of their ideas, security and visual quality.