Moire-free color halftone configuration employing common frequency vectors

• US 7,675,651 B2
• Filed: 11/30/2006
• Issued: 03/09/2010
• Est. Priority Date: 11/30/2006
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wang, Shen-Ge, Loce, Robert P
• Primary Examiner(s): LEE, TOMMY D
• Application Number:
  US11/565,434
• Publication Number:
  US 20080130055A1
• Time in Patent Office: 1,195 Days
• Field of Search: 358/1.1, 358/1.9, 358/3.04, 358/3.06, 358/3.09, 358/3.1, 358/533, 358/534, 358/536
• US Class Current: 358/3.06
• CPC Class Codes: H04N 1/4058 with details for producing a halftone screen at an oblique angle H04N1/4056 takes precedence
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

Abstract

Disclosed herein is a method and apparatus for moiré-free color halftone printing with up to four color image separations. The method and apparatus utilize a plurality of non-orthogonal halftone screens to produce outputs that are moiré free and form uniform periodic rosettes. The method and apparatus provide for defining a first and a second color halftone screen fundamental frequency vector for each of three halftone screens such that the halftone screen set output forms uniform hexagonal rosettes; then defining a fourth color halftone screen where a first fundamental vector of the fourth screen shares a fundamental frequency vector with one of said three halftone screens and a second fundamental frequency vector of the fourth screen shares a fundamental frequency vector with a different one of said three color halftone screens.

Claims

1. An image forming method for digitally reproducing a moiré

-free color halftone image using a halftone screen set consisting of a halftone screen for each color, the method comprising;

using a color halftoning screening apparatus to perform;

defining a first color halftone screen having a first fundamental frequency vector V_c1 and second fundamental frequency vector V_c2;

defining a second color halftone screen having a first fundamental frequency vector V_m1 and second fundamental frequency vector V_m2;

defining a third color halftone screen having a first fundamental frequency vector V_y1 and second fundamental frequency vector V_y2; and

,

selecting the values of the fundamental frequency vectors V_c1, V_c2, V_m1, and V_m2 such that the combinations satisfy the following;

V_c1−

V_m1=−

½

V_m2,

V_m2−

V_c2=−

½

V_c1, and

V_y1 equals one of V_c1, V_c2, V_m1, and V_m2; and

using said halftone screens, as further specified by said selected values of said fundamental frequency vectors, in an image forming apparatus for digital reproduction of a moiré

-free color halftone image.

2. The method of claim 1 further comprising:

defining a fourth color halftone screen having a first fundamental frequency vector V_k1, and second fundamental frequency vector V_k2;

selecting the values of the fundamental frequency vectors V_k1 and V_k2 such that combinations satisfy the following;

V_k2−

V_c2=½

V_c1,

V_c1−

V_k1=½

V_k2; and

defining the fundamental frequency vector V_y2 to equal one of V_c1, V_c2, V_m1, V_m2, V_k1, and V_k2 and not equal to ±

V_y1.

3. The method of claim 2 further comprising:

selecting the values of the fundamental frequency vectors such that combinations further satisfy at least one of the following;

V_c1−

V_m1+V_k2=0, and

V_c2−

V_m2−

V_k1=0.

4. The method of claim 2 wherein the defined fourth color halftone screen having a first fundamental frequency vector V_k1 and second fundamental frequency vector V_k2, comprises the color black.

5. The method of claim 2 wherein a resultant halftone screen set output comprises hexagon rosettes of identical shape and are two-dimensionally periodic.

6. The method of claim 1 further comprising:

selecting the values of the fundamental frequency vectors such that combinations further satisfy at least one of the following;

V_c1−

V_m1+V_k2=0, and

V_c2−

V_m2−

V_k1=0.

7. The method of claim 1 wherein the defined first color halftone screen having a first fundamental frequency vector V_c1 and second fundamental frequency vector V_c2, comprises the color cyan.

8. The method of claim 1 wherein the defined second color halftone screen having a first fundamental frequency vector V_m1 and second fundamental frequency vector V_m2, comprises the color magenta.

9. The method of claim 1 wherein the defined third color halftone screen having a first fundamental frequency vector V_y1 and second fundamental frequency vector V_y2, comprises the color yellow.

10. A method for generating a plurality of non-orthogonal halftone screen outputs for moiré

free color halftoning, the method comprising;

defining, using a color halftoning screening apparatus, a first and a second color halftone screen fundamental frequency vector for each of three halftone screens such that the halftone screen set output forms uniform hexagonal rosettes; and

,

defining, using a color halftoning screening apparatus, a fourth color halftone screen where a first fundamental vector of the fourth screen shares a fundamental frequency vector with one of said three halftone screens and a second fundamental frequency vector of the fourth screen shares a fundamental frequency vector with a different one of said three color halftone screens.

11. The method of claim 10, wherein the fourth color halftone screen is used to form a yellow halftone image separation.

12. The method of claim 10, wherein said three color halftone screens are used to form cyan, magenta, and black halftone image separations.

13. A color halftoning screening apparatus for reproducing a moiré

-free color halftone image using a halftone screen set consisting of a halftone screen for each color, the apparatus comprising;

a first color halftone screen having a first fundamental frequency vector V_c1 and second fundamental frequency vector V_c2;

a second color halftone screen having a first fundamental frequency vector V_m1 and second fundamental frequency vector V_m2 wherein combinations of the fundamental frequency vectors V_c1, V_c2, V_m1, and V_m2 satisfy the following;

V_c1−

V_m1=−

½

V_m2,

V_m2−

V_c2=−

½

V_c1, and

a third color halftone screen having a first fundamental frequency vector V_y1 and second fundamental frequency vector V_y2, where V_y1 equals one of V_c1, V_c2, V_m1, and V_m2.

14. The apparatus of claim 13 further comprising:

a fourth color halftone screen having a first fundamental frequency vector V_k1 and second fundamental frequency vector V_k2, wherein the values of the fundamental frequency vectors V_k1 and V_k2 satisfy the following;

V_k2−

V_c2=½

V_c1,

V_c1−

V_k1=½

V_k2; and

the fundamental frequency vector V_y2 is equal one of V_c1, V_c2, V_m1, V_m2, V_k1, and V_k2, and not equal to ±

V_y1.

15. The apparatus of claim 14 where the defined first color halftone screen having a first fundamental frequency vector V_c1 and second fundamental frequency vector V_c2, comprises the color cyan.

16. The apparatus of claim 14 wherein the defined second color halftone screen having a first fundamental frequency vector V_m1 and second fundamental frequency vector V_m2, comprises the color magenta.

17. The apparatus of claim 14 where the defined third color halftone screen having a first fundamental frequency vector V_y1 and second fundamental frequency vector V_y2, comprises the color yellow.

18. The apparatus of claim 14 where the defined fourth color halftone screen having a first fundamental frequency vector V_k1 and second fundamental frequency vector V_k2, comprises the color black.

19. The apparatus of claim 14 where a resultant halftone screen set output comprises hexagon rosettes of identical shape and are two-dimensionally periodic.