Tinted edge enhancement using harmonic halftones for the boundary pixels

• US 20060087694A1
• Filed: 10/26/2004
• Published: 04/27/2006
• Est. Priority Date: 10/26/2004
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Loce, Robert P., Xu, Beilei, Lieberman, David J., Hains, Charles M., McElvain, Jon S., Gwaltney, Mark A., Purdum, Connie F.
• Granted Patent: US 7,688,473 B2
• Time in Patent Office: Days
• US Class Current: 358/3.200
• 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 1/4092 Edge or detail enhancement

Abstract

Disclosed herein is an image processing method for producing enhanced halftone edges, particularly suited to those edges which only lie upon the background as apposed to those edges which abut other halftone screens. It utilizes a step of defining border pixels and a step of halftoning those border pixels in a different manner than the halftoning applied to the interior region of the tint or image segment. The preferred halftone for the border pixels will be related to the interior halftone by some number of common spatial frequency harmonics. Examples of common-harmonic screening for an edge include, but are not limited to: (a) same screen with different tone reproduction characteristics (boosted edge values); (b) same screen angles and frequencies with a different spot function, possibly phase shifted; (c) a dot screen whose frequency vectors can be generated by the frequency vectors of the interior screen; (d) a line screen whose frequency vectors can be generated by the frequency vectors of the interior screen. This generation process is directed to ensuring that the two screens will be “harmonically matched” where at least one of the fundamental frequency vectors and harmonics of the first screen will equal at least one of the fundamental frequency vectors and harmonics of the second screen.

Claims

1. An image processing method for producing image objects with enhanced halftone edges comprising:

defining border pixels of an image object;

selecting a first halftone screen having a first fundamental frequency and a first angle for printing the image object; and

selecting a second halftone screen having a second fundamental frequency and a second angle for printing the defined border pixels, wherein the second frequency and second angle are harmonically matched to the first frequency and first angle.

2. The method of claim 1, wherein the first and second halftone screens comprise dot screens and wherein the first and second angles are rotated 45°

from one another and the first fundamental frequency is √

2 multiple of the second fundamental frequency.

3. The method of claim 1, wherein the first halftone screen comprises a dot screen and the second halftone screen comprises a line screen;

wherein the first and second angles are substantially the same; and

wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

4. The method of claim 1, wherein the first halftone screen comprises a dot screen and the second halftone screen comprises a line screen and wherein the first and second angles are rotated 45°

from one another and the first fundamental frequency is √

2 multiple of the second fundamental frequency.

5. The method of claim 1, wherein the first and second halftone screens comprise line screens having the same angle and wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

6. The method of claim 1, wherein the first and second halftone screens comprise line screens and wherein the first and second angles are rotated 90°

from one another and wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

7. The method of claim 1, wherein the first and second halftone screens comprise non-orthogonal cells.

8. A method for minimizing boundary effects by producing enhanced edges for image objects, comprising:

defining border pixels of an image object;

selecting a first halftone screen having a first fundamental frequency and a first angle for printing pixels of a first object type for rendering the image object; and

selecting a second halftone screen having a second fundamental frequency and a second angle for printing pixels of a second object type for rendering the defined border pixels, wherein the second frequency and second angle are harmonically matched to the first frequency and the first angle.

9. The method of claim 8, wherein the first and second halftone screens comprise dot screens and wherein the first and second angles are rotated 45°

from one another and the first fundamental frequency is √

2 multiple of the second fundamental frequency.

10. The method of claim 8, wherein the first halftone screen comprises a dot screen and the second halftone screen comprises a line screen;

wherein the first and second angles are substantially the same; and

wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

11. The method of claim 8, wherein the first halftone screen comprises a dot screen and the second halftone screen comprises a line screen and wherein the first and second angles are rotated 45°

from one another and the first fundamental frequency is √

2 multiple of the second fundamental frequency.

12. The method of claim 8, wherein the first and second halftone screens comprise line screens having the same angle and wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

13. The method of claim 8, wherein the first and second halftone screens comprise line screens and wherein the first and second angles are rotated 90°

from one another and wherein the first fundamental frequency is an integer multiple of the second fundamental frequency.

14. The method of claim 8, wherein the first and second halftone screens comprise non-orthogonal cells.

15. An image processing method for producing image segments with enhanced halftone edges comprising:

defining border pixels of an image segment;

selecting a first halftone screen having a first fundamental frequency and a first angle for rendering the image segment; and

selecting a second halftone screen having a second fundamental frequency and a second angle for rendering the defined border pixels, wherein the second frequency and second angle are harmonically matched to the first frequency and first angle.

16. The method of claim 15, wherein the defined border pixels are just inside the edge of the image segment.

17. The method of claim 15, wherein the defined border pixels are just outside the edge of the image segment.

18. The method of claim 15, wherein the defined border pixels are comprised of pixels both just inside and just outside the edge of the image segment.