Method for moire-free color halftoning using non-orthogonal cluster screens

• US 6,798,539 B1
• Filed: 10/30/2000
• Issued: 09/28/2004
• Est. Priority Date: 10/30/2000
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wang, Shen-Ge, Fan, Zhigang, Wen, Zhenhuan
• Primary Examiner(s): ROGERS, SCOTT A
• Application Number:
  US09/698,104
• Time in Patent Office: 1,429 Days
• Field of Search: 358/1.9, 358/3.2, 358/3.26, 358/533, 358/534, 358/535, 358/536, 358/3.17
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

Abstract

The invention provides methods for using single-cell non-orthogonal cluster screens to satisfy the moiré-free conditions for color halftoning. The invention also provides methods that combine single-cell non-orthogonal cluster screens and line screens for moiré-free color halftoning. Particularly, the selection of these single-cell halftone screens is determined by satisfying moiré-free conditions provided in the respective spatial or frequency equations.

Claims

1. A method of generating a plurality of non-orthogonal halftone screens for substantially moiré

-free color halftoning, comprising;

locating non-orthogonal halftone cells substantially specified by two spatial vectors (x_n1, y_n1) and (x_n2, y_n2) that substantially form a non-orthogonal halftone cell, where, x_n1, y_n1 and x_n2, y_n2 are substantially integer valued;

identifying combinations of the located non-orthogonal halftone cells, suitable for tiling an image plane, of at least three of the located non-orthogonal halftone cells, where the spatial vectors of the identified combinations satisfy;

2. The method according to claim 1, wherein non-orthogonal includes cell shapes containing right angles.

3. The method according to claim 1, further comprising:

applying constraints to the located non-orthogonal halftone cells; and

removing non-orthogonal halftone cells that do not satisfy the constraints from the located non-orthogonal halftone cells.

4. The method according to claim 3, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

5. The method according to claim 1, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

6. The method according to claim 1, wherein, the identifying combinations step, identifies less than three of the located non-orthogonal halftone cells.

7. A method of generating a plurality of non-orthogonal halftone screens for substantially moiré

-free color halftoning, comprising;

locating non-orthogonal halftone cells substantially specified by two spatial vectors (x_n1, y_n1) and (x_n2, y_n2) that substantially form a non-orthogonal halftone cell, where, x_n1, y_n1 and x_n2, y_n2 are substantially integer valued;

locating halftone line screens substantially specified by two spatial vectors (x_m1, y_m1) and (x_m2, y_m2) that substantially form a halftone line screen, where, x_m1, y_m1 and x_m2, y_m2 are substantially integer valued while satisfying;

either y_m1=0 and y_m2=1,

or x_m1=0 and x_m2=1;

identifying combinations of the located non-orthogonal halftone cells and at least one of the located halftone line screens, suitable for tiling an image plane, of at least three of the located non-orthogonal halftone cells and line screens where the spatial vectors of the identified combinations satisfy;

8. The method according to claim 7, wherein non-orthogonal includes cell shapes containing right angles.

9. The method according to claim 7, further comprising:

applying constraints to the located non-orthogonal halftone cells; and

removing non-orthogonal halftone cells that do not satisfy the constraints from the located non-orthogonal halftone cells.

10. The method according to claim 9, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

11. The method according to claim 7, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

12. The method according to claim 7, wherein, the identifying combinations step, identifies less than three of the located non-orthogonal halftone cells and located line screens.

13. An apparatus for generating non-orthogonal halftone screens for substantially moiré

-free color halftoning, comprising;

a non-orthogonal halftone cell locating circuit, routine or agent that locates substantially non-orthogonal halftone cells that are substantially specified by two spatial vectors (x_n1, y_n1) and (x_n2, y_n2) where, x_n1, y_n1 and x_n2, y_n2 are substantially integer valued;

a non-orthogonal halftone cell combination identifying circuit, routine or agent that identifies combinations, suitable for tiling an image plane, of at least three of the located non-orthogonal halftone cells where the spatial vectors of the identified combinations satisfy;

14. The apparatus according to claim 13, wherein non-orthogonal includes cell shapes containing right angles.

15. The apparatus according to claim 13, further comprising:

a located non-orthogonal halftone cell removing circuit, routing or agent that removes located non-orthogonal cells according to a set of locating constraints.

16. The apparatus according to claim 15, further comprising:

a non-orthogonal halftone cell combination removing circuit, routine or agent that removes non-orthogonal halftone cell combinations according to a set of combination removing constraints.

17. The apparatus according to claim 13, further comprising:

a non-orthogonal halftone cell combination removing circuit, routine or agent that removes non-orthogonal halftone cell combinations according to a set of combination removing constraints.

18. The apparatus according to claim 13, wherein the non-orthogonal halftone cell combination identifying circuit, routine or agent identifies less than three non-orthogonal halftone cells of the located non-orthogonal halftone cells.

19. The apparatus according to claim 13, wherein the non-orthogonal halftone cell locating circuit, routine or agent also locates line screens substantially specified by two spatial vectors (x_m1, y_m1) and (x_m2, y_m2) that substantially form a halftone line screen, where, x_m1, y_m1 and y_m2, y_m2 are substantially integers while satisfying:

either y_m1=0 and y_m2=1,

or x_m1=0 and x_m2=1, where,

m=a, b, c;

the non-orthogonal halftone cell combination identifying circuit, routine or agent identifies combinations of the located non-orthogonal halftone cells and at least one of the located halftone line screens, suitable for tiling an image plane, of at least three of the located non-orthogonal halftone cells and line screens where the spatial vectors of the identified combinations satisfy;

20. The apparatus according to claim 19, further comprising:

a located non-orthogonal halftone cell and line screen removing circuit, routing or agent that removes located non-orthogonal cells and line screens according to a set of locating constraints.

21. The apparatus according to claim 20, further comprising:

a non-orthogonal halftone cell combination and line screen removing circuit, routine or agent that removes non-orthogonal halftone cell and line screen combinations according to a set of combination removing constraints.

22. The apparatus according to claim 19, further comprising:

a non-orthogonal halftone cell combination and line screen removing circuit, routine or agent that removes non-orthogonal halftone cell and line screen combinations according to a set of combination removing constraints.

23. The apparatus according to claim 19, wherein the non-orthogonal halftone cell and line screen combination identifying circuit, routine or agent identifies less than three non-orthogonal halftone cells and line screens of the located non-orthogonal halftone cells and line screens.

24. A method for using a plurality of non-orthogonal halftone screens for substantially moiré

-free color halftoning, comprising;

inputting an image data;

converting the image data to a halftone image data;

using a plurality of tileable halftone screens that contain combinations of non-orthogonal halftone cells where each non-orthogonal halftone cell is substantially specified by two spatial vectors (x_n1, y_n1) and (x_n2, y_n2), where, x_n1, y_n1 and x_n2, y_n2 are substantially integer valued;

identifying combinations of the located non-orthogonal halftone cells, suitable for tiling an image plane, of at least three of the located non-orthogonal halftone cells where the spatial vectors of the identified combinations satisfy;

25. The apparatus according to claim 24, wherein non-orthogonal includes cell shapes containing right angles.

26. The method according to claim 24, further comprising:

applying constraints to the located non-orthogonal halftone cells; and

removing non-orthogonal halftone cells that do not satisfy the constraints from the located non-orthogonal halftone cells.

27. The method according to claim 26, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

28. The method according to claim 24, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells; and

removing combinations of non-orthogonal halftone cells that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells.

29. The method according to claim 24, wherein, the identifying combinations step, identifies less than three of the located non-orthogonal halftone cells.

30. A method for using a plurality of non-orthogonal halftone screens for substantially moiré

-free color halftoning, comprising;

inputting an image data;

converting the image data to a halftone image data;

using a plurality of tileable halftone screens that contain combinations of located non-orthogonal halftone cells and line screens;

where,

each non-orthogonal halftone cell is substantially specified by two spatial vectors (x_n1, y_n1) and (x_n2, y_n2), where, x_n1, y_n1 and x_n2, y_n2 are substantially integer valued, where,

each line screen is substantially specified by two spatial vectors (x_m1, y_m1) and (x_m2, y_m2) that substantially form a halftone line screen, where, x_m1, y_m1 and x_m2, y_m2 are substantially integer values while satisfying;

either y_m1=0 and y_m2=1,

or x_m1=0 and x_m2=1, where,

the spatial vectors of the combinations of located non-orthogonal halftone cells and line screens satisfy;

31. The method according to claim 30, wherein non-orthogonal includes cell shapes containing right angles.

32. The method according to claim 30, further comprising:

applying constraints to the located non-orthogonal halftone cells and line screens; and

removing non-orthogonal halftone cells and line screens that do not satisfy the constraints from the located non-orthogonal halftone cells and line screens.

33. The method according to claim 32, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells and line screens; and

removing combinations of non-orthogonal halftone cells and line screens that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells and line screens.

34. The method according to claim 30, further comprising:

applying constraints to the identified combinations of non-orthogonal halftone cells and line screens; and

removing combinations of non-orthogonal halftone cells and line screens that do not satisfy the constraints from the identified combinations of non-orthogonal halftone cells and lines screens.

35. The method according to claim 30, wherein, the identifying combinations step, identifies less than three of the located non-orthogonal halftone cells and line screens.