A system and method for classifying an image block of a printed image into contone, halftone, or error diffusion classes, includes scanning the printed image; selecting an n by n block of pixels from the scanned image in a luminance channel; calculating an array of DCT coefficients of the pixel block,...http://www.google.de/patents/US7424151?utm_source=gb-gplus-sharePatent US7424151 - Method and system for image classification and halftone frequency detection
