Contrast-Enhanced Visual Cryptography Schemes Based on Perfect Reconstruction of White Pixels and Additional Basis Matrix

Abstract

The existing pixel patterns for the visual cryptography scheme are based on the Perfect Reconstruction of Black Pixels (PRBP). Mathematically in PRBP the white pixels are represented by 0 and the black pixel by 1. In the usual binary image, the number of white pixels is much larger than the number of black pixels. Therefore, the perfect reconstructions of black pixels in visual cryptography schemes can decrease the contrast. Here, a visual cryptography scheme which is focused on the Perfect Reconstruction of White Pixels (PRWP) and hence can provide better clarity is presented. As in the case of all existing binary image file formats, PRWP represents white pixel by 1 and black pixel by 0. The visual cryptography scheme with PRWP can improve the clarity of reconstructed images. But by analysing the experimental results, we know that the number of black pixels in the reconstructed image is very less compared to the original image. Therefore increasing the black pixels in the reconstructed image can improve the contrast. In order to increase the black pixels use Additional Basis Matrix (ABM) to represent the new pixel pattern.