Image Hatching for Visual Cryptography

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.