JUCS - Journal of Universal Computer Science 21(12): 1536-1562, doi: 10.3217/jucs-021-12-1536
On Real-valued Visual Cryptographic Basis Matrices
expand article infoNeil Buckley, Atulya K. Nagar, Subramanian Arumugam§
‡ Liverpool Hope University, Liverpool, United Kingdom§ Kalasalingam University, Anand Nagar, India
Open Access
Abstract
Visual cryptography (VC) encodes an image into noise-like shares, which can be stacked to reveal a reduced quality version of the original. The problem with encrypting colour images is that they must undergo heavy pre-processing to reduce them to binary, entailing significant quality loss. This paper proposes VC that works directly on intermediate grayscale values per colour channel and demonstrates real-valued basis matrices for this purpose. The resulting stacked shares produce a clearer reconstruction than in binary VC, and to the best of the authors' knowledge, is the first method posing no restrictions on colour values while maintaining the ability to decrypt with human vision. Grayscale and colour images of differing entropies are encrypted using fuzzy OR and XOR, and their PSNR and structural similarities are compared with binary VC to demonstrate improved quality. It is compared with previous research and its advantages highlighted, notably in high quality reconstructions with minimal processing.
Keywords
visual cryptography, secret sharing, cryptanalysis; colour images, image processing