System and method of reducing aliasing in printed images

• US 20040113921A1
• Filed: 12/16/2002
• Published: 06/17/2004
• Est. Priority Date: 12/16/2002
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Kang, Sang-Chul, Hains, Charles M.
• Granted Patent: US 6,943,808 B2
• Time in Patent Office: Days
• US Class Current: 345/611
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: H04N 1/4055 producing a clustered dots or a size modulated halftone pattern

Abstract

The system and method reduces aliasing which is formed by the patterns that are introduced by the halftone screens used in the printer. The system and method provides halftone-specific anti-alias filters for obtaining optimal effective resolution in printed images. A method of reducing aliasing in a digital image includes providing a digital image; selecting a halftone screen for halftoning the digital image, wherein the halftone screen has a directional component associated with it; filtering the digital image with an antialiasing filter, the antialiasing filter having been designed to have a directional frequency response that is optimized for the directional component of the selected halftone screen; and halftoning the filtered digital image.

Claims

1. A method of reducing aliasing in a digital image, comprising:

providing a digital image;

selecting a halftone screen for halftoning the digital image, wherein the halftone screen has a directional component associated with it;

filtering the digital image with an antialiasing filter, the antialiasing filter having been designed to have a directional frequency response that is optimized for the directional component of the selected halftone screen; and

halftoning the filtered digital image.

2. The method of claim 1, wherein the halftone screen comprises a line screen having a defined screen angle;

and

wherein the antialiasing filter comprises an elliptical filter oriented substantially in the direction perpendicular to the defined screen angle.

3. The method of claim 1, wherein the halftone screen comprises a clustered dot screen having orthogonal dots and a defined screen angle;

and

wherein the antialiasing filter comprises a four lobed structure formed by two ellipses superimposed and rotated ninety degrees apart, one of the ellipses of the four lobed structure being oriented substantially in the direction perpendicular to the defined screen angle.

4. The method of claim 1, wherein the halftone screen comprises a clustered dot screen having non-orthogonal dots and two defined screen angles;

and

wherein the antialiasing filter comprises a four lobed structure formed by two ellipses superimposed, each of the two ellipses of the four lobed structure being oriented substantially in the direction perpendicular to one of the defined screen angles.

5. The method of claim 1, wherein the antialiasing filter further comprises a small effect to compensate for high addressability in one direction.

6. The method of claim 1, wherein the antialiasing filter further comprises a small second order effect to compensate for directionality effects in the horizontal and vertical directions.

7. A system for processing digital document images having reduced aliasing in digital images;

comprising;

an image source for providing a digital image;

a controller for selecting a halftone screen for halftoning the digital image, wherein the halftone screen has a directional component associated with it;

an antialiasing filter for filtering the digital image prior to halftoning, the antialiasing filter having been designed to have a directional frequency response that is optimized for the directional component of the selected halftone screen; and

a halftone module for halftoning the filtered digital image.

8. The system of claim 7, wherein the halftone screen comprises a line screen having a defined screen angle;

and

wherein the antialiasing filter comprises an elliptical filter oriented substantially in the direction perpendicular to the defined screen angle.

9. The system of claim 7, wherein the halftone screen comprises a clustered dot screen having orthogonal dots and a defined screen angle;

and

wherein the antialiasing filter comprises a four lobed structure formed by two ellipses superimposed and rotated ninety degrees apart, one of the ellipses of the four lobed structure being oriented substantially in the direction of the defined screen angle.

10. The system of claim 7, wherein the halftone screen comprises a clustered dot screen having non-orthogonal dots and two defined screen angles;

and

wherein the antialiasing filter comprises a four lobed structure formed by two ellipses superimposed, each of the two ellipses of the four lobed structure being oriented substantially in the direction perpendicular to one of the defined screen angles.

11. The system of claim 7, wherein the antialiasing filter further comprises a small effect to compensate for high addressability in one direction.

12. The system of claim 7, wherein the antialiasing filter further comprises a small second order effect to compensate for directionality effects in the horizontal and vertical directions.