Extended color visual cryptography for black and white secret image

•We propose the (k,n)(k,n) colored-black-and-white extended visual cryptography scheme (CBW-EVCS).•Our (k,n)(k,n)-CBW-EVCS has the extended ability revealing meaningful shadow images.•We extend the conditions of (k,n)(k,n)-CWB-EVCS to those of (k,n)(k,n)-CWB-EVCS.•We prove that our constructions satisfy security, contrast, and cover image conditions.

Recently, De Prisco and De Santis introduced a (k,n)(k,n) colored-black-and-white visual cryptography scheme (CBW-VCS), which adopts colored pixels in shadow images to share a black and white secret image. Only k   or more participants can reconstruct the secret image by combining their shadow images. It seems that no one study (k,n)(k,n)-CBW-VCS with the extended ability revealing meaningful shadow images (denoted as CBW-extended VCS (CBW-EVCS)). In this paper, we extend the conventional EVCS (i.e., BW-EVCS) to the CBW-EVCS. This paper has two main contributions: (i) we construct (k,n)(k,n)-CWB-EVCSs, (ii) all constructions are proven to satisfy security, contrast, and cover image conditions.