HOW TO CONSTRUCT PROGRESSIVE VISUAL CRYPTOGRAPHY SCHEMES

A visual cryptography scheme (VCS) is an encryption method for images that does not need a computer to decode a secret image. In this paper we propose a simple, progressive VCS which is constructed from a traditional threshold VCS. Our progressive VCS has better decoded image quality and flexibility than the Fang Lin scheme, a previous progressive VCS. We also present a block-wise progressive VCS which has jigsaw puzzle like decryption, and an XOR-based progressive VCS without pixel expansion. We give some experimental results which show that our scheme is superior to the Fang Lin scheme with respect to the decoded image quality and the decoding speed controllability.