Methods and systems for background color extrapolation

• US 8,014,596 B2
• Filed: 10/31/2007
• Issued: 09/06/2011
• 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.
• Primary Examiner(s): Do; Anh Hong
• Application Number:
  US11/930,486
• Publication Number:
  US 20090110319A1
• Time in Patent Office: 1,406 Days
• Field of Search: 382/164, 382/118, 382/162, 382/173, 382/232, 382/239, 382/260, 382/299, 382/302, 358/518, 358/528, 375/240.05, 375/E7.026, 104/203, 104/224
• 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 determining a background color in a digital image. A background color value for a pixel in an image may be determined by summarizing the color values in a color buffer, wherein the color values in the buffer may have been selectively added to the color buffer, from the image data, based on one, or more, criteria which may be related to edge density, image uniformity, non-local color information, a foreground color estimate and other selection criterion. The background color for the pixel maybe determined in a forward scan and updated during a backward scan.

Claims

1. A method for determining a background color at a pixel of interest in a digital image, said method comprising:

in an image-processing system, 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 image-processing system, receiving a color value for said pixel of interest;

in said image-processing system, receiving a control signal associated with said pixel of interest;

in said image-processing system, receiving a first background color estimate, wherein said first background color estimate is associated with said first scan line;

in said image-processing system, receiving a previous background color estimate, wherein said previous background color estimate is associated with a previous scan line in said digital image;

in said image-processing system, calculating a first color difference between said color value for said pixel of interest and said first background color estimate;

in said image-processing system, calculating a second color difference between said color value for said pixel of interest and said previous background color estimate; and

in said image-processing system, determining a first-scan background color estimate for said pixel of interest based on said control signal, said first color difference and said second color difference.

2. A method according to claim 1, wherein said control signal is a multi-value control signal.

3. A method according to claim 1, wherein said control signal comprises at least one of a background label for said pixel of interest, an edge label for said pixel of interest and a pictorial label for said pixel of interest.

4. A method according to claim 1 further comprising determining if said pixel of interest is a glyph pixel.

5. A method according to claim 1, wherein:

said calculating a first color difference comprises calculating a first color distance; and

said calculating a second color difference comprises calculating a second color distance.

6. A method according to claim 1 further comprising:

comparing said first color difference to said second color difference when said first color difference meets a first condition relative to a first threshold or said second color difference meets a second condition relative to a second threshold; and

when said comparing said first color difference to said second color difference produces a first result;

updating a second color buffer with said color value for said pixel of interest;

summarizing said second color buffer, thereby producing a second color buffer background color; and

assigning said second color buffer background color to said first-scan background color estimate; and

when said comparing said first color difference to said second color difference produces a second result;

updating a third color buffer with said color value for said pixel of interest;

summarizing said third color buffer, thereby producing a third color buffer background color; and

assigning said third color buffer background color to said first-scan background color estimate.

7. A method according to claim 1 further comprising, when said first color difference meets a third condition relative to a first threshold and said second color difference meets a forth condition relative to a second threshold:

receiving a text-density feature measure for a region substantially proximate to said pixel of interest; and

assigning said first scan background color estimate based on said text-density feature measure.

8. A method according to claim 1 further comprising:

associating said pixel of interest with a second scan line with an associated second scan direction in said digital image; and

determining a second-scan background color estimate based on said first-scan background color estimate.

9. A method according to claim 8 further comprising determining if said pixel of interest is a glyph pixel.

10. A method according to claim 1, wherein said control signal comprises a background label for said pixel of interest, an edge label for said pixel of interest and a pictorial label for said pixel of interest.

11. A method according to claim 10 further comprising, when said background label indicates said pixel of interest is a background pixel and said edge label indicates said pixel of interest is not an edge pixel:

updating a first color buffer with said color value for said pixel of interest;

summarizing said first color buffer, thereby producing a first color buffer background color; and

assigning said first color buffer background color to said first-scan background color estimate.

12. A method according to claim 10 further comprising assigning a pictorial color value associated with said pixel of interest to said first-scan background color estimate when, said pictorial label indicates said pixel of interest is a pictorial pixel and said background label indicates said pixel of interest is a not a background pixel, or, said pictorial label indicates said pixel of interest is a pictorial pixel and said edge label indicates said pixel of interest is an edge pixel.

13. A method according to claim 10 further comprising:

associating said pixel of interest with a second scan line with an associated second scan direction in said digital image; and

determining a second-scan background color estimate based on said first-scan background color estimate.

14. A method according to claim 13 further comprising:

receiving an updated background label for said pixel of interest;

receiving a third background color estimate, wherein said third background color estimate is associated with said second scan line;

receiving a second-scan previous background color estimate, wherein said second-scan previous background color estimate is associated with a previously scanned line in said digital image;

calculating a third color difference between said color value for said pixel of interest and said third background color estimate;

calculating a fourth color difference between said color value for said pixel of interest and said second-scan previous background color estimate; and

determining a second scan background color estimate for said pixel of interest based on said updated background label, said edge label, said pictorial label, said third color difference and said fourth color difference.

15. A system for determining a background color at a pixel of interest in a digital image, said system comprising:

a pixel-of-interest selector for selecting 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;

background-label receiver for receiving a background label for said pixel of interest;

an edge-label receiver for receiving an edge label for said pixel of interest;

a pictorial-label receiver for receiving a pictorial label for said pixel of interest;

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

a first-background-color-estimate receiver for receiving a first background color estimate associated with said first scan line;

a previous-background-color-estimate receiver for receiving a previous background color estimate associated with a previous scan line in said digital image;

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

a second color-difference calculator for calculating a second color difference between said color value for said pixel of interest and said previous background color estimate; and

a first-scan background-color determiner for determining a first-scan background color estimate for said pixel of interest based on said background label, said edge label, said pictorial label, said first color difference and said second color difference.

16. A system according to claim 15 further comprising a glyph determiner for determining if said pixel of interest is a glyph pixel.

17. A system according to claim 15, wherein

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

and

said second color-difference calculator comprises a second color-distance calculator for calculating a second color distance between said color value for said pixel of interest and said previous background color estimate.

18. A system according to claim 15 further comprising:

a first comparator for determining when said background label indicates said pixel of interest is a background pixel and said edge label indicates said pixel of interest is not an edge pixel;

a first color-buffer updater for updating a first color buffer with said color value for said pixel of interest when said first comparator determines said background label indicates said pixel of interest is a background pixel and said edge label indicates said pixel of interest is not an edge pixel;

a first color-buffer summarizer for summarizing said first color buffer, thereby producing a first color buffer background color, when said first comparator determines said background label indicates said pixel of interest is a background pixel and said edge label indicates said pixel of interest is not an edge pixel; and

a first assigner for assigning said first color buffer background color to said first-scan background color estimate when said first comparator determines said background label indicates said pixel of interest is a background pixel and said edge label indicates said pixel of interest is not an edge pixel.

19. A system according to claim 15 further comprising a pictorial-color-value assigner for assigning a pictorial color value associated with said pixel of interest to said first-scan background color estimate when, said pictorial label indicates said pixel of interest is a pictorial pixel and said background label indicates said pixel of interest is a not a background pixel, or, said pictorial label indicates said pixel of interest is a pictorial pixel and said edge label indicates said pixel of interest is an edge pixel.

20. A system according to claim 15 further comprising:

a color-difference comparer for comparing said first color difference to said second color difference when said first color difference meets a first condition relative to a first threshold or said second color difference meets a second condition relative to a second threshold;

a second-color-buffer updater for updating a second color buffer with said color value for said pixel of interest when said comparing said first color difference to said second color difference produces a first result;

a second-color-buffer summarizer for summarizing said second color buffer, thereby producing a second color buffer background color when said comparing said first color difference to said second color difference produces a first result;

a second-color-buffer assigner for assigning said second color buffer background color to said first-scan background color estimate when said comparing said first color difference to said second color difference produces a first result;

a third-color-buffer updater for updating a third color buffer with said color value for said pixel of interest when said comparing said first color difference to said second color difference produces a second result;

a third-color-buffer summarizer for summarizing said third color buffer, thereby producing a third color buffer background color when said comparing said first color difference to said second color difference produces a second result; and

a third-color-buffer assigner for assigning said third color buffer background color to said first-scan background color estimate when said comparing said first color difference to said second color difference produces a second result.

21. A system according to claim 15 further comprising:

a text-density-feature receiver for receiving a text-density feature measure for a region substantially proximate to said pixel of interest when said first color difference meets a third condition relative to a first threshold and said second color difference meets a forth condition relative to a second threshold; and

a first-scan assigner for assigning said first scan background color estimate based on said text-density feature measure when said first color difference meets a third condition relative to a first threshold and said second color difference meets a forth condition relative to a second threshold.

22. A system according to claim 15 further comprising:

a scan-line associater for associating said pixel of interest with a second scan line with an associated second scan direction in said digital image; and

a second-scan background-color determiner for determining a second-scan background color estimate based on said first-scan background color estimate.

23. A system according to claim 22 further comprising a glyph determiner for determining if said pixel of interest is a glyph pixel.

24. A system according to claim 22 further comprising:

an updated-background-label receiver for receiving an updated background label for said pixel of interest;

a third-background-color-estimate receiver for receiving a third background color estimate, wherein said third background color estimate is associated with said second scan line;

a second-scan previous-background-color-estimate receiver for receiving a second-scan previous background color estimate, wherein said second-scan previous background color estimate is associated with a previously scanned line in said digital image;

a third color difference calculator for calculating a third color difference between said color value for said pixel of interest and said third background color estimate;

a fourth color difference calculator for calculating a fourth color difference between said color value for said pixel of interest and said second-scan previous background color estimate; and

a second-scan background color estimator for determining a second-scan background color estimate for said pixel of interest based on said updated background label, said edge label, said pictorial label, said third color difference and said fourth color difference.