Visual Cryptography for Gray-Level Image using Adaptive Order Dither Technique

Abstract

Visual cryptography Scheme (VCS), an emergingcryptography technology, uses the characteristics of humanvision to decrypt encrypted images without requirement ofcomplex computation. Naor and Shamir proposed the basicmodel of visual cryptography for binary images. Since thenresearchers have published many papers related to this model,but only few papers have been published related to gray-levelimages. In this paper, a new technique for visual cryptographyof gray-level image is proposed, which uses first adaptive orderdither technique to convert a given gray level image into anapproximate binary image. Then, the existing visualcryptography scheme for binary image is applied to accomplishcreation of shares. The overall effect of the proposed method isthe achievement of visual encryption and decryption functionsfor gray-level images, where the quality of decrypted image isbetter compared to the decrypted image obtained by VCS usingSpace-filling curve order dither technique. This is shown byexperimental results based on the objective measurementtechnique.

Keywords

• VCS
• HVS
• SFCOD
• Halftone
• Dithering