HALFTONE DETECTION USING TRANSITION COUNTING
Original Publication Date: 1980-Dec-31
Included in the Prior Art Database: 2004-Apr-02
Xerox Disclosure Journal
A halftone detection circuit 5 using transition counting is employed to find halftone areas on the printed page and allow reproduction of a document that contains mixed line copy and halftone areas. In the block diagram of the figure, pixel data is provided from a suitable source such as Raster Input Scanner (RIS) 6. A block counter 7, driven by the system pixel clock breaks a scan line into blocks of pixels of length X. The pixel data is output by RIS 6 to a transistion counter 8 which counts the positive transitions of the pixel data within the block. A comparator 9 compares the count on counter 8 at the end of the block with a preset number N. If the number of transitions exceeds the preset number N, then the block is declared a halftone area. If the number of transitions is N or less, the block is determined to be not halftone.