Methods and Systems for Glyph-Pixel Selection

• US 20090110320A1
• Filed: 10/31/2007
• Published: 04/30/2009
• Est. Priority Date: 10/30/2007
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Speigle, Jon M., Ferman, Ahmet Mufit, Campbell, Richard J.
• Granted Patent: US 8,121,403 B2
• Time in Patent Office: Days
• US Class Current: 382/260
• 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:

a. 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;

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

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

d. 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;

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

f. 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;

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

h. comparing said dynamic threshold with said first color difference;

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

j. 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:

a. 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

b. 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:

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

b. computing an average of said first plurality of color differences.

4. A method according to claim 3 further comprising:

a. receiving a page background color value estimate; and

b. 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 first condition and said page-value color difference and a second threshold meet a second condition, thereby meeting a third 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 third condition is not met and said range and a third threshold meet a fourth condition and said average and a fourth threshold meet a fifth 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:

a. 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;

b. a first background-color receiver for receiving a first background color estimate for said pixel of interest;

c. a pixel-of-interest color value receiver for receiving a pixel-of-interest color value for said pixel of interest;

d. 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;

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

f. 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;

g. a dynamic threshold determiner for determining a dynamic threshold based on said first plurality of color differences;

h. a threshold comparator for comparing said dynamic threshold with said first color difference; and

i. 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:

a. 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

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

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

12. A system according to claim 11 further comprising:

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

b. 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 further comprises setting said dynamic threshold to a rejection value when said average and a first threshold meet a first condition and said page-value color difference and a second threshold meet a second condition, thereby meeting a third 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 further comprises setting said dynamic threshold to an acceptance value when said third condition is not met and said range and a third threshold meet a fourth condition and said average and a fourth threshold meet a fifth 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:

a. determining a pixel of interest in a digital image;

b. receiving a label value associated with said pixel of interest;

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

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

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

f. 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.