International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Visual Cryptography Schemes with Optimal Pixel Expansion

Carlo Blundo
Stelvio Cimato
Alfredo De Santis
Search ePrint
Search Google
Abstract: A visual cryptography scheme encodes a black&white secret image into n shadow images called shares which are distributed to the n participants. Such shares are such that only qualified subsets of participants can ``visually'' recover the secret image. Usually, the reconstructed image will be darker than the background of the image itself. In this paper we consider visual cryptography schemes satisfying the model introduced by Tzeng and Hu (Designs, Codes and Cryptography, Vol. 27, No. 3, pp. 207-227, 2002). In such a model the recovered secret image can be darker or lighter than the background. We prove a lower bound on the pixel expansion of the scheme and, for (2,n)-threshold visual cryptography schemes, we provide schemes achieving the bound. Our schemes improve on the ones proposed by Tzeng and Hu.
  title={Visual Cryptography Schemes with Optimal Pixel Expansion},
  booktitle={IACR Eprint archive},
  keywords={Visual cryptography, Pixel expansion.},
  note={ 13284 received 16 May 2006},
  author={Carlo Blundo and Stelvio Cimato and Alfredo De Santis},