US 5,402,245 AGranted

Bi-level digital color printer system exhibiting improved undercolor removal and error diffusion procedures

AssigneeHewlett-Packard Company

InventorsRicardo J. Motta, Andrew E. Fitzhugh, Michael D. McGuire, Gary J. Dispoto

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Abstract

A system selectively enables a printer to deposit on a sheet C, M, Y and K color dots at each of the plurality of pixel locations to produce a color image. The system comprises a memory for storing C, M, Y and K color values for each pixel in the color image and a processor for controlling selective deposition of the C, M, Y and K colors. The processor determines a gray value for each pixel location from values stored in the C, M, and Y color planes. The processor subtracts the determined gray value from the C, M, and Y values which correspond to the pixel location and then determines a relationship of the gray value to a non-linear function and in dependence upon the relationship alters the C, M and Y pixel values accordingly. The processor either (1) adds the gray value back to the C, M, and Y values for the pixel location, or (2) adds a first portion of the gray value to the C, M, and Y values for the pixel location and a second portion of the gray value to the K value for the pixel location; or (3) adds all of the gray value to a K value for the pixel location. As a result, the C, M, Y and K values are altered in accordance with the determined gray value. The altered color values are then prioritized and the processor determines which colors should be printed at each pixel location and diffuses color error values to neighboring pixel locations after such determination. The prioritization procedure enables print priority to be given to either the brightest color dot or to the color dot that is most visible to the human eye.

Claims15

Dependent claims

A system for selectively enabling a digital printer to deposit on a sheet, Cyan (C), Magenta (M), Yellow (Y) and Black (K) color dots at each of a plurality of pixel locations, to produce a color image, said system comprising:

memory means for storing planes of C, M, Y and K color values for each pixel in the color image;
processor means coupled to said memory means, said processor means
(i) determining a gray value for each pixel location from said color values stored in said C, M, and Y color planes and for subtracting a determined gray value for a pixel location from C, M, and Y values corresponding to said pixel location,
(ii) determining in what segment of a non-linear function that defines a curve having plural segments said determined gray value is located,
(iii) based upon a location of said determined gray value, creating changed color values for each said pixel location by:
(a) adding said gray value to said C, M, and Y color values for said pixel location, if said gray value is located in a first segment of the curve defined by said non-linear function, or
(b) adding a portion of said gray value to said C, M, and Y color values for said pixel location and another portion of said gray value to a K color value for said pixel location, if said gray value is located in a second segment of the curve defined by said non-linear function, or
(c) adding all said gray value to a K value for said pixel location, if said gray value is located in a third segment of the curve defined by said non-linear function, and
(iv) diffusing color error values to neighboring pixel locations;
and print means responsive to said processor means for printing said color image comprising error diffused color values transmitted from said processor means.

7 more elements

Dependencies are inferred from the claim text.