Hybrid quantization method for color document reproduction

Claim 1

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.

Claim 9

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.

Claim 10

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.