Quantization method for color document reproduction in a color printing system

• US 6,643,030 B1
• Filed: 12/15/1999
• Issued: 11/04/2003
• Est. Priority Date: 12/15/1999
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Cheng, Xiaoxue, Loce, Robert P.
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US09/464,517
• Time in Patent Office: 1,420 Days
• Field of Search: 358/1.9, 358/3.26, 358/533, 358/536, 358/534, 358/535, 358/3.14, 358/3.2, 358/515
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

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.

Claims

1. 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.

2. A method as defined in claim 1 wherein said at least four color separations include cyan, magenta, yellow and black.

3. A method as defined in claim 1, wherein among separations, at least one separation is a preferred separation for screen angle sharing.

4. A method as defined in claim 1, wherein image segments determined to be suitable sharing screen angles are identified by a data tag, independently of the image received.

5. A method as defined in claim 4, wherein data tags for said image segment are processed to control application of screen sharing.

6. A method as defined in claim 5, wherein said data tag processing includes morphological processing to smooth application of screen angle sharing over said image or said image segment.

7. A method as defined in claim 1, wherein said image segment suitability is determined from a frequency of use of separation screen angle sharing.

8. A method as defined in claim 1, wherein said image segment suitability is determined from an object type to be processed in a received image.

9. A method as defined in claim 1, wherein said image segment suitability is determined by a spatial configuration of screen angles to be shared for a particular region of the received image.

10. A method as defined in claim 1, wherein said image segment suitability is user determined, via a user interface.

11. A method as defined in claim 1, wherein two separations will share screen angles, one of which will be a yellow separation.

12. A method as defined in claim 1, wherein for two image segments, at least one of which is determined to be suitable for screen angle sharing, a blending process is applied, mixing each image segments screen angle sharing over a border between.

13. A method as defined in claim 1, wherein said determination of separations that will share screen angles includes

identifying a yellow separation;

from among a cyan, magenta and black separation, determining which separation has a lowest density;

identifying said separation with a lowest density as a separation suitable for sharing screen angles, with said yellow separation.

14. A method as defined in claim 13, wherein said identifying suitability for sharing screen angles is provided by a data tag, independent of the image received.

15. A method as defined in claim 14, wherein data tags for said image segment are processed to control application of screen sharing.

16. A method as defined in claim 15, wherein said data tag processing includes morphological processing to smooth application of screen sharing over said image or said image segment.

17. A method as defined in claim 1, wherein prior to said image suitability determination, gray color replacement is applied, whereby density of at least one separation other than yellow is substantially reduced.

18. A method as defined in claim 1, wherein separations sharing screen angles are each reproduced with a distinct halftone matrix.

19. A method as defined in claim 1, wherein separations sharing screen angles are reproduced with halftone cells therein out of phase with each other.

20. A method as defined in claim 1, wherein said determination of separations that will share screen angles includes

identifying a yellow separation;

from among a cyan, magenta and black separation, determining which separations have a density less than a predetermined threshold;

identifying a separation with a density less than a predetermined threshold as suitable for sharing screen angles, with said yellow separation.

21. A method as defined in claim 20, wherein signals in said identified separations are identified by a data tag, independent of the image received.

22. A method as defined in claim 20, wherein data tag signals in said image segment are processed to control application of screen sharing.

23. A method as defined in claim 22, wherein said processing included comparison of characteristics of a spatial distribution of said tags, for selection of a screen for screen sharing.

24. A method as defined in claim 22, wherein said data tag processing includes morphological processing to smooth application of screen sharing over said image or said image segment.

25. A method as defined in claim 20, wherein among separations, at least one separation is a preferred separation for screen angle sharing.

26. A method as defined in claim 25, wherein thresholding, said at least one preferred separation is weighted to favor selection in selection processing.

27. 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.

28. A method as defined in claim 27, where prior to said image suitability determination, gray color replacement is applied, whereby density of at least one separation other than yellow is substantially reduced.

29. A method as defined in claim 27, wherein separations sharing screen angles are each reproduced with a distinct halftone matrix.

30. A method as defined in claim 27, wherein separations sharing screen angles are reproduced with halftone cells therein out of phases with each other.

31. 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.

32. A device as defined in claim 31, wherein said predetermined value is greater than 0.

33. A device as defined in claim 31, wherein said plurality of separations include cyan, magenta, yellow and black separations, and said second halftone process processes said yellow separation.

34. A device as defined in claim 31, wherein said first halftone process processes one of said cyan, magenta and black separations.

35. A device as defined in claim 31, wherein said separations received at said separation input have been previously subjected to gray component removal.

36. A device as defined in claim 31, wherein said adaptive controller adds at least one control bit for said screen matrix generator, identifying which halftone processors should be provided with screen matrices with identical screen angles.