Visual cryptography

About: Visual cryptography is a research topic. Over the lifetime, 1724 publications have been published within this topic receiving 25300 citations.

Image hatching for visual cryptography

Abstract: Image hatching (or nonphotorealistic line-art) is a technique widely used in the printing or engraving of currency. Diverse styles of brush strokes have previously been adopted for different areas of an image to create aesthetically pleasing textures and shading. Because there is no continuous tone within these types of images, a multilevel scheme is proposed, which uses different textures based on a threshold level. These textures are then applied to the different levels and are then combined to build up the final hatched image. The proposed technique allows a secret to be hidden using Visual Cryptography (VC) within the hatched images. Visual cryptography provides a very powerful means by which one secret can be distributed into two or more pieces known as shares. When the shares are superimposed exactly together, the original secret can be recovered without computation. Also provided is a comparison between the original grayscale images and the resulting hatched images that are generated by the proposed algorithm. This reinforces that the overall quality of the hatched scheme is sufficient. The Structural SIMilarity index (SSIM) is used to perform this comparison.

Size-invariant extended visual cryptography with embedded watermark based on error diffusion

Abstract: A (2, 2) extended visual cryptography scheme with meaningful shares and no pixel expansion is constructed in this paper. In addition to the secret image, an additional watermark is also embedded to serve for authentication purpose. This watermark can be recovered by stacking a shifted version of one share with the other share. More importantly, the recovered watermark and secret images are free from interferences from the cover images.

Visual Cryptography Schemes with Perfect Reconstruction of Black Pixels

Abstract: Conventional visual cryptography (VC) suffers from a pixel-expansion problem, or an uncontrollable display quality problem for recovered images, and lacks a general approach to construct visual secret sharing schemes (VSSs) for general access structures (GASs). We propose here in a general and systematic approach to address these issues without sophisticated codebook design. The approach can be used for binary secret images in non-computer-aided decryption environments. To avoid pixel expansion, we design a set of column vectors to encrypt secret pixels rather than use the conventional VC-based approach. We begin by formulating a mathematic model for the VC construction problem to find the column vectors for the optimal VC construction, after which we develop a simulated-annealing-based algorithm to solve the problem. It indicates that the display quality of the recovered image is superior to that of previous studies.

New size-reduced visual secret sharing schemes with half reduction of shadow size

Abstract: Visual Secret Sharing (VSS) scheme proposed by Naor and Shamir is a perfect secure scheme to share the secret image. By using m subpixels to represent one pixel, the secret image is divided into several shadow images whose size is m times than the secret image. The value of m is known as the pixel expansion. In this paper, we propose the new size-reduced VSS schemes and dramatically decrease the pixel expansion to a half and meantime the contrast is not compromised.