Tinted edge enhancement using harmonic halftones for the boundary pixels

• US 7,688,473 B2
• Filed: 10/26/2004
• Issued: 03/30/2010
• Est. Priority Date: 10/26/2004
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: McElvain, Jon S., Gwaltney, Mark A., Purdum, Connie F., Loce, Robert P., Xu, Beilei, Lieberman, David J., Hains, Charles M.
• Primary Examiner(s): Poon; King Y
• Assistant Examiner(s): Washington; Jamares
• Application Number:
  US10/973,725
• Publication Number:
  US 20060087694A1
• Time in Patent Office: 1,981 Days
• Field of Search: 358/298, 358/1.9, 358/533, 358/3.06, 358/462, 358/536, 358/3.2, 358/1.1, 382/173, 382/263, 382/264, 382/266, 382/268, 382/269
• US Class Current: 358/3.2
• 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, with a computational device, a pixel border region and an interior region within an image object, the image object initially having a first halftone screen having a first fundamental frequency and a first angle,

the pixel border region comprising border pixels adjacent to an edge of the image object,

the interior region being adjacent to and separate from the pixel border region,

the edge of the image object abutting an untoned background, and

wherein the pixel border region comprises a portion lying between the interior region and the untoned background;

printing pixels within the interior region using the first halftone screen; and

selecting, with the computational device, a second halftone screen having a second fundamental frequency and a second angle for printing pixels within the pixel border region,

the second halftone screen selected to have a boosted contone level relative to the first halftone screen wherein the second frequency and second angle are harmonically matched to the first frequency and first angle, and wherein the boosted contone level is determined based upon values stored in at least one pre-defined lookup table that are associated with a combination of contone levels in the interior region and upon contone levels in the pixel border region.

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 an integer multiple of a square root of 2 and 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 an integer multiple of a square root of 2 and 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, with a computational device, a pixel border region and an interior region associated with an image object, the pixel border region comprising border pixels adjacent to an edge of the image object and the interior region being adjacent to and separate from the pixel border region;

selecting, with the computational device, a first halftone screen having a first fundamental frequency and a first angle for printing pixels of a first object type for rendering pixels within the interior region; and

selecting, with the computational device, a second halftone screen having a boosted contone level relative to the first halftone screen and having a second fundamental frequency and a second angle for printing pixels of a second object type for rendering pixels within the pixel border region, wherein the second frequency and second angle are harmonically matched to the first frequency and the first angle, and

wherein the boosted contone level is determined based upon values stored in at least one pre-defined lookup table that are associated with a combination of contone levels in the interior region and upon contone levels in the pixel border region.

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 an integer multiple of a square root of 2 and 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 an integer multiple of a square root of 2 and 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, the method comprising:

defining, with a computational device, a pixel border region and an interior region associated with an image segment having an initial halftone screen, the pixel border region comprising border pixels adjacent to an edge of the image segment and the interior region being adjacent to and separate from the pixel border region;

selecting, with the computational device, a first halftone screen having a first fundamental frequency and a first angle for rendering pixels within the interior region; and

selecting, with the computational device, a second halftone screen having a boosted contone level relative to the first halftone screen and having a second fundamental frequency and a second angle for rendering pixels within the pixel border region, wherein the second frequency and second angle are harmonically matched to the first frequency and first angle, and

wherein the boosted contone level is determined based upon values stored in at least one pre-defined lookup table that are associated with a combination of contone levels in the interior region and upon contone levels in the pixel border region.

16. The method of claim 15, wherein the pixel border region is just inside the edge of the image segment.

17. The method of claim 15, wherein the pixel border region is just outside the edge of the image segment.

18. The method of claim 15, wherein the pixel border region is both just inside and just outside the edge of the image segment.

19. The method of claim 15, wherein the edge of the image object abuts an untoned background, and wherein the pixel border region comprises a portion lying between the interior region and the untoned background.

20. The method of claim 15, wherein the selecting the first halftone screen selects the initial halftone screen as the first halftone screen.