Edge contrast adjustment filter

• US 8,971,658 B2
• Filed: 04/23/2007
• Issued: 03/03/2015
• Est. Priority Date: 04/23/2007
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Lin, Guo-Yau, McElvain, Jon
• Primary Examiner(s): TSAI, TSUNG YIN
• Application Number:
  US11/789,051
• Publication Number:
  US 20080260284A1
• Time in Patent Office: 2,871 Days
• Field of Search: None
• US Class Current: 382/266
• CPC Class Codes: G06T 2207/10008 from scanner, fax or copier
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 2207/30176 Document
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/15 Cutting or merging image elements, e.g. region growing, watershed or clustering-based techniques
• CPC Class Codes: H04N 1/58 Edge or detail enhancement; Noise or error suppression, e.g. colour misregistration correction H04N1/62 takes precedence

Abstract

Disclosed herein is a method that includes a classifier that distinguishes objects based on their color shades. A moving window based operator looks at the color class of the adjacent objects and determines if an adjustment is necessary. If at least one of the objects is the type of interest and the color classes of the objects meet the criteria, then the boundary between the objects is subject to be adjusted. Two adjustment modes are discussed: “adjust-tagging” mode and “adjust-color” mode. In the adjust-tagging mode, a specific tag is sent down to the print engine to force the use of high addressability halftones for the boundary pixels in the darker object. In the adjust-color mode, a color lighter (usually white) than that of the lighter object is assigned to the boundary pixels in the lighter object. The width of the modified pixels along the boundary is configurable.

Claims

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

scanning with a scanner a digital image having a plurality of objects to obtain scanline data;

applying by an image processor an edge enhancement filter to the scanline data, including;

classifying each object into a set of shade classes,

adding objects tagged as being associated with a first shade class to an event list, and

adjusting a parameter if the added object is adjacent to an object classified in a second shade class;

generating an output format that includes contone and tag/hint planes; and

compressing the output format and sending the compressed output format to a printing system.

2. The method of claim 1, wherein the parameter to be adjusted is color.

3. The method of claim 1, wherein the parameter to be adjusted is a tag.

4. The method of claim 1, wherein the parameters to be adjusted are color and a tag.

5. The method of claim 1, wherein the shade classes for each separation comprise WHITE, HIGHLIGHT, MIDTONE_AND_ABOVE, and OTHER.

6. The method of claim 5, wherein for each separation the shade class may be defined as:

if 0≦

digital count≦

white threshold, this separation is said to be WHITE;

if white threshold<

digital count≦

highlight threshold, this separation is said to be HIGHLIGHT;

if highlight threshold<

digital count≦

midtone threshold, this separation is said to be OTHER;

if midtone threshold<

digital count≦

255, this separation is said to be MIDTONE_AND_ABOVE.

7. The method of claim 1, wherein the shade classes to be added in the event list are a subset of all possible shade classes.

8. The method of claim 7, wherein the shade class of a multi-channel color space is determined by the shade class types of its separations:

if the darkest separation is HIGHLIGHT and at least one separation is HIGHLIGHT, the color is said to be HIGHLIGHT;

else if at least one separation is MIDTONE, the color is said to be MIDTONE;

else if all separations are WHITE, the color is said to be WHITE;

else the color is said to be OTHER.

9. The method of claim 8, wherein the multi-channel color space is CMYK or RGB.

10. The method of claim 9, further comprising a mechanism to ignore the edges that have transition between HIGHLIGHT and MIDTONE_AND_ABOVE for a lighter color separation.

11. The method of claim 10, wherein the lighter color separation is a Yellow.

12. The method of claim 8, wherein the multi-channel color space is N-channel, where N is greater than or equal to zero.

13. An edge enhancement filtering method comprising:

applying by an image processor an edge enhancement filter to scanline data of a digital image, including;

classifying each object into a set of shade classes;

identifying edge pixels associated with adjacent objects that transition between a first shade class and a second shade class;

determining whether the edge pixels need adjustment between the transitions;

tagging the edge pixels to include at least one pixel width of a different color at an interface of an object portion of the transitions;

generating an output format that includes contone and tag/hint planes; and

, compressing the output format and sending the compressed output format to a printing system.

14. The method of claim 13, wherein the two different shade classes are HIGHLIGHT and MIDTONE.

15. The method of claim 13, the modification occurs at the edge pixels with a configurable radius in the lighter object.

16. The method of claim 15, wherein the newly modified color is even lighter than that of the lighter object.

17. The method of claim 16, wherein the lighter color is WHITE.

18. The method of claim 13, wherein the modification occurs at the edge pixels in the darker object.

19. An edge enhancement filtering method for a printing system with a rendering tagging mechanism comprising:

applying by an image processor an edge enhancement filter to the scanline data, including;

classifying each object into a set of shade classes,

adding objects tagged as being associated with a first shade class to an event list, and

adjusting a parameter if the added object is adjacent to an object classified in a second shade class, wherein the adjustment includes modifying a tag plane to force a high addressability screen;

generating an output format that includes contone and tag/hint planes; and

compressing the output format and sending the compressed output format to a printing system.

20. The method of claim 19, wherein the modification occurs at the edge pixels in the darker object.

21. The method of claim 20, a newly modified tag utilizes the high addressable halftones.

22. An image processing method for producing objects with enhanced halftone edges, the method comprising:

scanning a digital image having a plurality of objects to obtain scanline data;

applying an edge enhancement filter to the scanline data, including;

classifying each object into a set of shade classes,

modifying an edge pixel or contone value between two objects of different shade classes,

identifying and tagging edges associated with certain shade types,

adding edges associated with a first shade,

examining whether the edge needs adjustment between highlight-midtone transitions,

adjusting the parameter at the boundary pixel if a select mode is enabled, and

placing at least one pixel width of white frame at an interface of a highlight portion;

generating an output format that includes contone and tag/hint planes; and

,

compressing the output format and sending the compressed output format to a printing system.