Retrieval of gray images from digital halftones

Presents a new method for retrieving a gray picture from an orthographic halftone image. It gives substantially better detail than the traditional low-pass filtering approach. The screen parameters are first estimated. The pixel value of the halftone then reveals the possible gray range of the pixel value in the original continuous tone image. The gray range obtained here is broad. It is narrowed down by logic filtering. The logic filtering is basically an operation combining the gray range data in the neighborhood of a pixel. Its adaptive nature makes it possible to remove the screen effects while retaining the edge information. The algorithms for screen parameter estimation and logic filtering are described