Browse Prior Art Database

Original Publication Date: 1984-Jun-30
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


When processing halftones, halftone images must be discriminated from line copy images, and a key element in effecting this accurately is an image classifier circuit. Referring to drawing Figure 1, a classifier circuit 2 is shown which has been found to yield extremely good discrimination results between halftone and line copy images. Classifier circuit 2 processes the image data in binary form and compares blocks of image data from neighboring lines with a corresponding block of image data from the line being processed using registers 4, 5, 6 and exclusive OR register 8. The output of register 8 is summed by digital summer 9 and combined with an established threshold level signal derived from microprocessor 10 to provide an 8- bit address to threshold register 11. The threshold level output of register 11 is compared to a preset peak by peak detector control 12 and the smaller value output to 4-bit counter 14. The output of counter 14 resets digital comparators 15, 16. The count on comparators 15, 16 is compared by halftone detect circuit 18 which in response sets a 16-bit control counter 20 to the appropriate count. The signal from counter 20 is compared with that of halftone level register 22 by digital comparator 21 to provide a control signal in line 23 indicating either the presence or absence of halftone images.