Digital image - Protection by means of cryptographic mixing transformations

A lot of research studies have been devoted to image - protection, either by cryptographic methods (e.g. Opt. Eng. 35, Sept. 1996) or by watermarking technique (e.g. Proc. SPIE Vol. 3971). In a previous study, the authors reconsidered and improved the cryptographic mixing transformations proposed by CE Shannon for natural language, obtaining a strong cipher for images, as well. The present paper goes deeply inside of the image-protection problem: (1) by presenting some variants for the cryptographic mixing transformations which are good even when burst errors appear in the cryptogram; (2) by enabling the use of an m-gram substitution in the mixing functions; (3) by advancing a bridge between cryptographic methods and watermaking techniques. The illustrations are obtained out of processing: (a) computer-simulated random images obeying different probability laws and autocorrelation functions, (b) natural images, and (c) test images.