Extended visual cryptography scheme with aspect ratio invariant

Conventional visual cryptography scheme (VCS) generates noise-like random pixels on shares to hide secret images by expanding a secret pixel to m sub pixels. m is not a square integer, and results in the distortion of recovered image. Most existing aspect ratio invariant VCSs generated share images are meaningless. It suffers a management problem which dealers cannot visually identify each share. In this paper, we firstly analyze the property of the extended matrix. Then we present a construction which implements the meaningful shares with aspect ratio invariant based on the above property. And our scheme like the original extended visual cryptography scheme (EVCS) does that every secret pixel is exactly reconstructed. The pixel expansion and the contrast of recovered image approximately equals convention VCS under the premise of keeping the aspect ratio invariant.