Quantization method for color document reproduction in a color printing system
AssigneeXerox Corporation
InventorsRobert P. Loce, Xiaoxue Cheng
Life of this patent
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Abstract
The present invention is a method and apparatus for reducing two-color moiréoften found during the rendering of full color images using halftoning techniques, by providing shared screen angles between distinct color separations.
Claims36
In a color reproduction device, reproducing images in at least four color separations, each color separation printed with a screen at a selected screen angle, a method of sharing screen angles between distinct color separations including:
- for a received image segment, determining suitability for separation screen angle sharing;
- for an image segment determined to be suitable, determining separations that will share screen angles;
- processing said image segment with shared screen angles.
A four color printer, printing superposed separations with cyan, magenta, yellow and black separations, each separation including at least a portion thereof halftoned, a method of sharing screen angles between distinct color separations including
- from said cyan, magenta and black separations, determining for a selected area one of said separations with a minimum density;
- printing cyan, magenta and black separations with halftones at widely separated screen angles;
- printing said yellow separation at a same screen angle as said separation with said minimum density.
A halftoning system, for use in a reproduction device printing a plurality of separations comprising:
- a separation input, receiving said plurality of separations for printing, each separation representing a distinct printer colorant, and including a plurality of image signals described as “c”-level signals;
- a plurality of halftone processors, quantizing image signals received in said separations into “d”-level signals, where d<c, suitable for reproduction at said reproduction device, each halftone processor responsive to a screen matrix having a predetermined screen angle and phase, directed thereto for said quantizing process;
- a screen generator, providing screen matrices at selected screen angles and selected phases to each halftone processor;
- an adaptive halftone controller, controlling operation of said halftone processors, by providing commands to said screen generator regarding screen matrices, screen angles and/or phases;
- said adaptive halftone controller operative to direct said halftone screen generator to direct screen matrices with identical screen angles to a first and a second halftone processor in said plurality thereof, when density within a selected set of said image signals in said separation quantized by said first halftone processor is less than a predetermined value.
Dependencies are inferred from the claim text.