Hybrid quantization method for color document reproduction
AssigneeXerox Corporation
InventorsThomas M. Holladay, Reiner Eschbach
Life of this patent
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Abstract
An image processing system for preparing a color document for printing, each discrete area or pixel in the image described by a signal having a number of possible states greater than can be rendered by a selected printer, in which each separation of the image is halftoned, with at least one of the separations processed with a non-periodic halftoning method, and at least one of the remaining separations processed with a periodic pattern. Preferably, in a printer printing with colorants approximating cyan, magenta, yellow and black, one of the non-yellow separations is processed with the non-periodic halftoning method.
Claims15
A color printing system, including a processor preparing color documents for printing, said color documents each including a plurality of separations, each separation defined with a set of image signals describing optical density with m density levels, while a destination printer is capable of rendering density with n density levels, comprising:
- a printer, adapted to print a plurality of color separations, so that when the separations are superposed on a final substrate, a selected color is defined;
- a source of image signals describing a color document with a like plurality of color separations, each image signal representing optical density with one of m levels for a discrete area of a separation;
- a first halftone processor operatively connected to said source of image signals and reducing the number of levels m representing optical density in a non-zero, predetermined subset of the separations to a number of levels n representing optical density, said means generating a periodic pattern thereby;
- a second halftone processor operatively connected to said source of image signals for reducing the number of levels m representing optical density in at least one remaining separation to a number of levels n representing optical density, said means generating a non-periodic pattern thereby;
- an image processor directing signals processed at each halftone processor to said printer to print said processed color image.
A method of preparing color documents for printing, said color documents each including a plurality of separations, each separation defined with a set of image signals describing optical density with set of m density levels, while a destination printer is capable of rendering density with n density levels, the steps including:
- receiving a set of image signals describing a color document with a like plurality of color separations, each image signal representing optical density with one of m levels for a discrete area of a separation;
- for a non-zero predetermined subset of the color separations, halftoning the m level image signals to n level image signals, in a manner generating a periodic pattern having a fixed frequency for the predetermined subset, and a distinct fixed angle for each of the plurality of separations;
- for a non-zero remaining subset of the color separations, halftoning the m level image signals to n level image signals, in a substantially stochastic manner;
- directing halftoned signals to a printer adaptable to print n levels to print said color image so that when the separations are superposed on a final substrate, a selected color is defined.
A color printing system, including a processor preparing color documents for printing, said color documents each including a plurality of separations, each separation defined with a set of image signals describing optical density with a set of m density levels, while a destination printer is capable of rendering density with n density levels, comprising:
- a printer, adapted to print separations of cyan, magenta, yellow and black, so that when the separations are superposed on a final substrate, a selected color is defined;
- a source of cyan, magenta, yellow and black image signals describing a color document, each image signal representing optical density with one of m levels for a discrete area of a separation;
- a first halftone processor operatively connected to said source of image signals for reducing the number of levels m representing optical density in said magenta, cyan and yellow separations to a number of levels n representing optical density, said means generating a periodic pattern thereby;
- a second halftone processor operatively connected to said source of image signals for reducing the number of levels m representing optical density in the black separation to a number of levels n representing optical density, said means generating a non-periodic pattern thereby;
- an image processor directing halftoned image data from the halftone processor to said printer.
Dependencies are inferred from the claim text.