Color transfer visual cryptography with perfect security

Recently, Luo et al. introduced the concept of the color transfer visual cryptographic scheme (CTVCS) by embedding the information of color channels R, G and B into the conventional (k,n)-VCS. Luo et al.'s (k,n)-CTVCS visually decoded the halftoned secret image by stacking any k shadow images similar to the conventional (k,n)-VCS and obtained a high-quality color image. However, Luo et al.'s (k,n)-CTVCS requires a key in the encoding and decoding phases and therefore it is, strictly speaking, not a threshold scheme with perfect security. In this study, we solved this security problem and proposed a (k,n)-CTVCS that does not require a key. This experiment indicated that the proposed solution achieves the same feature (obtaining the original color image) as Luo et al.'s (k,n)-CTVCS. In addition, we formally defined contrast and security conditions of a (k,n)-CTVCS and demonstrated that our constructions satisfied the contrast and security conditions of a (k,n)-CTVCS.