Methods and systems for glyph-pixel selection

• US 8,121,403 B2
• Filed: 10/31/2007
• Issued: 02/21/2012
• Est. Priority Date: 10/30/2007
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Campbell, Richard J., Speigle, Jon M., Ferman, Ahmet Mufit
• Primary Examiner(s): CHANG, JON CARLTON
• Application Number:
  US11/930,500
• Publication Number:
  US 20090110320A1
• Time in Patent Office: 1,574 Days
• Field of Search: 382/173, 382/176, 382/180, 382/164, 382/181, 358/464
• US Class Current: 382/164
• CPC Class Codes: H04N 1/40062 Discrimination between different image types, e.g. two-tone, continuous tone

Abstract

Aspects of the present invention are related to methods and systems for detecting glyph pixels in a digital image.

Claims

1. A method for glyph detection in a digital image, said method comprising:

determining a pixel of interest in a digital image, wherein said pixel of interest is part of a first scan line with an associated first scan direction in said digital image;

receiving a first background color estimate for said pixel of interest;

receiving a pixel-of-interest color value for said pixel of interest;

receiving a color value for each pixel in a first plurality of pixels in a region proximate to said pixel of interest, thereby producing a first plurality of color values;

calculating a first color difference between said pixel-of-interest color value and said first background color estimate;

calculating a color difference between said first background color estimate and each color value in said first plurality of color values, thereby producing a first plurality of color differences;

determining a dynamic threshold based on said first plurality of color differences;

comparing said dynamic threshold with said first color difference;

labeling said pixel of interest as a glyph pixel when said comparing meets a first condition; and

labeling said pixel of interest as a non-glyph pixel when said comparing meets a second condition.

2. A method according to claim 1, wherein:

said calculating a first color difference comprises calculating a first color distance between said pixel-of-interest color value and said first background color estimate; and

said calculating a color difference between said first background color estimate and each color value in said first plurality of color values comprises calculating a color distance between said first background color estimate and each color value in said first plurality of color values.

3. A method according to claim 1, wherein said determining a dynamic threshold comprises:

determining a range of said first plurality of color differences; and

computing an average of said first plurality of color differences.

4. A method according to claim 3 further comprising:

receiving a page background color value estimate; and

computing a page-value color difference between said page background color value estimate and said pixel-of-interest color value.

5. A method according to claim 4, wherein said determining a dynamic threshold further comprises setting said dynamic threshold to a rejection value when said average and a first threshold meet a third condition and said page-value color difference and a second threshold meet a fourth condition, thereby meeting a fifth condition.

6. A method according to claim 5, wherein said pixel-of-interest color value comprises a plurality of color channels and said rejection value is the summation of the maximum of each of said plurality of color channels.

7. A method according to claim 5, wherein said determining a dynamic threshold further comprises setting said dynamic threshold to an acceptance value when said fifth condition is not met and said range and a third threshold meet a sixth condition and said average and a fourth threshold meet a seventh condition.

8. A method according to claim 7, wherein said acceptance value is said minimum of said first plurality of color differences.

9. A system for glyph detection in a digital image, said system comprising:

in a computing device, a pixel-of-interest selector for determining a pixel of interest in a digital image, wherein said pixel of interest is part of a first scan line with an associated first scan direction in said digital image;

in said computing device, a first background-color receiver for receiving a first background color estimate for said pixel of interest;

in said computing device, a pixel-of-interest color value receiver for receiving a pixel-of-interest color value for said pixel of interest;

in said computing device, a color value receiver for receiving a color value for each pixel in a first plurality of pixels in a region proximate to said pixel of interest, thereby producing a first plurality of color values;

in said computing device, a first difference calculator for calculating a first color difference between said pixel-of-interest color value and said first background color estimate;

in said computing device, a color difference calculator for calculating a color difference between said first background color estimate and each color value in said first plurality of color values, thereby producing a first plurality of color differences;

in said computing device, a dynamic threshold determiner for determining a dynamic threshold based on said first plurality of color differences;

in said computing device, a threshold comparator for comparing said dynamic threshold with said first color difference; and

in said computing device, a classifier for labeling said pixel of interest as a glyph pixel when said comparing meets a first condition and for labeling said pixel of interest as a non-glyph pixel when said comparing meets a second condition.

10. A system according to claim 9, wherein:

said first difference calculator comprises a first distance calculator for calculating a first color distance between said pixel-of-interest color value and said first background color estimate; and

said color difference calculator comprises a color distance calculator for calculating a color distance between said first background color estimate and each color value in said first plurality of color values.

11. A system according to claim 9, wherein said dynamic threshold determiner comprises:

a range determiner for determining a range of said first plurality of color differences; and

an averager for computing an average of said first plurality of color differences.

12. A system according to claim 11 further comprising:

a page-background-color receiver for receiving a page background color value estimate; and

a page-background difference calculator for computing a page-value color difference between said page background color value estimate and said pixel-of-interest color value.

13. A system according to claim 12, wherein said dynamic threshold determiner sets said dynamic threshold to a rejection value when said average and a first threshold meet a third condition and said page-value color difference and a second threshold meet a fourth condition, thereby meeting a fifth condition.

14. A system according to claim 13, wherein said pixel-of-interest color value comprises a plurality of color channels and said rejection value is the summation of the maximum of each of said plurality of color channels.

15. A system according to claim 13, wherein said dynamic threshold determiner sets said dynamic threshold to an acceptance value when said fifth condition is not met and said range and a third threshold meet a sixth condition and said average and a fourth threshold meet a seventh condition.

16. A system according to claim 15, wherein said acceptance value is said minimum of said first plurality of color differences.

17. A method for glyph detection in a digital image, said method comprising:

determining a pixel of interest in a digital image;

receiving a label value associated with said pixel of interest;

receiving a first-scan background color estimate for said pixel of interest;

receiving a second-scan background color estimate for said pixel of interest;

calculating a background-color difference between said first-scan background color estimate and said second-scan background color estimate; and

changing said label value from said label value to a second label value when said background-color difference meets a first condition.

18. A method according to claim 17 further comprising updating a first color buffer with a color value associated with said pixel of interest when said background-color difference meets a first condition.

19. A method according to claim 18 further comprising associating a glyph pixel color with said pixel of interest, wherein said glyph pixel color is based on the contents of said first color buffer.

20. A method according to claim 17, wherein said calculating said background-color difference comprises calculating a color distance between said first-scan background color estimate and said second-scan background color estimate.

21. A method according to claim 17, wherein said first-scan background color estimate corresponds to a first scan direction and said second-scan background color estimate corresponds to a second scan direction.

22. A method according to claim 21, wherein said first-scan direction is a forward-scan direction and said second-scan direction is a backward-scan direction.