Moire-free color halftone configuration

• US 20060170975A1
• Filed: 12/08/2005
• Published: 08/03/2006
• Est. Priority Date: 01/28/2005
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wang, Shen-Ge
• Granted Patent: US 7,480,076 B2
• Time in Patent Office: Days
• US Class Current: 358/3.60
• 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 Moire-free color halftone configuration for clustered dots. Unlike conventional methods, the disclosed method produces periodic hexagon rosettes of identical shapes. These exemplary hexagon rosettes have three fundamental spatial frequencies exactly equal to half of the fundamental frequency of the three halftone screens. The resultant halftone outputs are truly Moire free, as all the fundamentals and harmonic frequencies are multiples of and thus higher in frequency than the rosette fundamental frequency. The halftone outputs resulting from the employment of the exemplary rosette design methodology provided herein, are also robust to the typical misregistration among color separations commonly found in color systems.

Claims

1. A method for forming non-orthogonal halftone screens for moiré

;

free color halftoning, comprising;

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; and

,

selecting the values of the fundamental frequency vectors to identify combinations that satisfy the following;

$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=-\frac{1}{2}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}$$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=-\frac{1}{2}<br><br>V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

2. The method of claim 1 further comprising:

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

selecting the values of the fundamental frequency vectors to identify combinations that further satisfy the following;

$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=\frac{1}{2}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}$$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=\frac{1}{2}<br><br>V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

3. The method of claim 1 further comprising:

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

selecting the values of the fundamental frequency vectors to identify combinations that further satisfy the following;

$V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}+V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=\frac{1}{2}<br><br>V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=-\frac{1}{2}<br><br>V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

4. The method of claim 2 further comprising:

selecting the values of the fundamental frequency vectors to identify combinations that further satisfy the following;

$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=0,\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=0.$

5. The method of claim 1 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.

6. The method of claim 1 where 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.

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

8. The method of claim 2 where a resultant halftone screen comprises hexagon rosettes of identical shape and two-dimension periodic.

14. The method of claim 8 where the resultant cluster screen comprises hexagon rosettes of identical shape and two-dimension periodic.

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

free color halftoning, comprising;

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; and

,

adjusting the values of the fundamental frequency vectors to identify combinations that satisfy where the sum of the first color halftone screen second fundamental frequency vector V_c2 and the second color halftone screen first fundamental frequency vector V_m1 equate to a function of the first color halftone screen first fundamental frequency vector V_c1, while also satisfying where the difference of the second color halftone screen second fundamental frequency vector V_m2 taken from the first color halftone screen first fundamental frequency vector V_c1 equates to a function of the second color halftone screen first fundamental frequency vector V_m1.

10. The method of claim 9 further comprising:

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

adjusting the values of the fundamental frequency vectors to identify combinations that further satisfy where the sum of the first color halftone screen first fundamental frequency vector V_c1, plus the second color halftone screen first fundamental frequency vector V_m1, minus the third color halftone screen first fundamental frequency vector V_k1 equates to zero, while also satisfying where the sum of the first color halftone screen second fundamental frequency vector V_c2, plus the second color halftone screen second fundamental frequency vector V_m2, minus the third color halftone screen second fundamental frequency vector V_k2 equates to zero.

11. The method of claim 9 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.

12. The method of claim 9 where 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.

13. The method of claim 10 where the defined third color halftone screen having a first fundamental frequency vector V_k1 and second fundamental frequency vector V_k2, comprises the color black.

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

free color halftoning, comprising;

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_k1 and second fundamental frequency vector V_k2; and

,

adjusting the values of the fundamental frequency vectors to identify combinations that satisfy the following;

$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=0,<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}-V_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=0,<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=-\frac{1}{2}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}$$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=-\frac{1}{2}<br><br>V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

16. The method of claim 15 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, 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, and the defined third color halftone screen having a first fundamental frequency vector V_k1 and second fundamental frequency vector V_k2, comprises the color black.

17. The method of claim 15 where the resultant cluster screen comprises hexagon rosettes of identical shape and two-dimension periodic.

18. A color screening apparatus providing a hexagon rosette for halftoning of image data in printed reproduction comprising:

a first color halftone screen including,

a first fundamental frequency vector V_c1 and a value associated therewith, as well as,

a second fundamental frequency vector V_c2 and a value associated therewith; and

,

a second color halftone screen including,

a first fundamental frequency vector V_m1 and a value associated therewith, as well as,

a second fundamental frequency vector V_m2 and a value associated therewith;

the values assigned said first and second color halftone screen fundamental frequencies being interrelated by;

$V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=-\frac{1}{2}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{c<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=-\frac{1}{2}<br><br>V_{m<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

19. The apparatus claim of claim 18 where the first color halftone screen is cyan.

20. The apparatus claim of claim 18 where the second color halftone screen is magenta.

21. The apparatus claim of claim 18 where the first color halftone screen is yellow.

22. The apparatus claim of claim 19 where the second color halftone screen is yellow.

23. A color screening apparatus providing a hexagon rosette for halftoning of image data in printed reproduction comprising:

a first color halftone screen including,

a first fundamental frequency vector V_x1, as well as,

a second fundamental frequency vector V_x2;

a second color halftone screen including,

a first fundamental frequency vector V_y1, as well as,

a second fundamental frequency vector V_y2; and

,

a third color halftone screen including,

a first fundamental frequency vector V_z1, as well as,

a second fundamental frequency vector V_z2;

said first, second and third color halftone screen fundamental frequencies being interrelated by;

$V_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>1}+V_{y<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{z<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=0,<br><br>V_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{y<br><br>\text{\hspace{1em}<br><br>}<br><br>2}-V_{z<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=0,<br><br>V_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+V_{y<br><br>\text{\hspace{1em}<br><br>}<br><br>1}=-\frac{1}{2}<br><br>V_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\mathrm{and}$$V_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>1}-V_{y<br><br>\text{\hspace{1em}<br><br>}<br><br>2}=-\frac{1}{2}<br><br>V_{y<br><br>\text{\hspace{1em}<br><br>}<br><br>1}.$

24. The apparatus claim of claim 23 where the first color halftone screen is cyan.

25. The apparatus claim of claim 23 where the second color halftone screen is magenta.

26. The apparatus claim of claim 23 where the third color halftone screen is black.

27. The apparatus claim of claim 23 where the second color halftone screen is yellow.