Data Structure for Coding Screened Halftone Pictures

A method of coding scanned documents containing halftone pictures, e.g. newspapers and magazines, for transmission purposes in prepress has been presented. The halftone screen is estimated and the gray value of each dot is found, thus giving a compact description. At the receiver the picture is re-screened. A new data structure and related algorithms for handling the digital screen without restrictions on the screen parameters has been presented. Data compression rates above 20 are obtained for halftone pictures The algorithms are suited for implementation using fast dedicated hardware. The rescreening can also be used as digital halftoning with arbitrary screens using look-up tables.