Methods and systems for detecting character content in a digital image
First Claim
Patent Images
1. A method for classifying a pixel in a digital image, said method comprising:
- a) determining a pixel of interest in a digital image;
b) evaluating a large-text-character condition for said pixel of interest and a first region substantially proximate to said pixel of interest, said first region comprising a first plurality of pixels and an associated first local background color estimate;
c) classifying said pixel of interest as a first-category pixel when said large-text-character condition is satisfied;
d) computing a dynamic threshold when said large-text-character condition is not satisfied, wherein said dynamic threshold is based on the color values in a second region substantially proximate to said pixel of interest, said second region comprising a second plurality of pixels and an associated second local background color estimate;
e) calculating a first similarity measure between said second local background color estimate and the color of said pixel of interest;
f) classifying said pixel of interest as a first-category pixel when said first similarity measure is greater than said dynamic threshold; and
g) classifying said pixel of interest as a second-category pixel when said first similarity measure is not greater than said dynamic threshold.
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Abstract
Embodiments of the present invention comprise systems and methods for detecting glyph pixels in a rasterized image.
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Citations
21 Claims
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1. A method for classifying a pixel in a digital image, said method comprising:
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a) determining a pixel of interest in a digital image; b) evaluating a large-text-character condition for said pixel of interest and a first region substantially proximate to said pixel of interest, said first region comprising a first plurality of pixels and an associated first local background color estimate; c) classifying said pixel of interest as a first-category pixel when said large-text-character condition is satisfied; d) computing a dynamic threshold when said large-text-character condition is not satisfied, wherein said dynamic threshold is based on the color values in a second region substantially proximate to said pixel of interest, said second region comprising a second plurality of pixels and an associated second local background color estimate; e) calculating a first similarity measure between said second local background color estimate and the color of said pixel of interest; f) classifying said pixel of interest as a first-category pixel when said first similarity measure is greater than said dynamic threshold; and g) classifying said pixel of interest as a second-category pixel when said first similarity measure is not greater than said dynamic threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A system for classifying a pixel in a digital image, said system comprising:
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a) in an image processing device, a pixel selector for determining a pixel of interest in a digital image; b) in said image processing device, a large-text evaluator for evaluating a large-text-character condition for said pixel of interest and a first region substantially proximate to said pixel of interest, said first region comprising a first plurality of pixels and an associated first local background color estimate; c) in said image processing device, a first classifier for classifying said pixel of interest as a first-category pixel when said large-text-character condition is satisfied; d) in said image processing device, a dynamic threshold calculator for computing a dynamic threshold when said large-text-character condition is not satisfied, wherein said dynamic threshold is based on the color values in a second region substantially proximate to said pixel of interest, said second region comprising a second plurality of pixels and an associated second local background color estimate; e) in said image processing device, a first similarity measure calculator for calculating a first similarity measure between said second local background color estimate and the color of said pixel of interest; f) in said image processing device, a second classifier for classifying said pixel of interest as a first-category pixel when said first similarity measure is greater than said dynamic threshold; and g) in said image processing device, a third classifier for classifying said pixel of interest as a second-category pixel when said first similarity measure is not greater than said dynamic threshold. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for classifying a pixel in a digital image, said method comprising:
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a) determining a pixel of interest in a digital image; b) receiving a local background color estimate for a region substantially proximate to said pixel of interest, wherein said region comprises a plurality of pixels; c) receiving a page background color estimate for said digital image; d) calculating a similarity measure between said local background color estimate and the color of said pixel of interest, wherein said similarity measure comprising calculating the distance between the color of said local background color estimate and the color of said pixel of interest; e) classifying said pixel of interest as a first-category pixel when said similarity measure is not greater than a similarity threshold and said local background color estimate is not equivalent to said page background color estimate; f) calculating a contrast measure between a plurality of pixels in said region and said local background color when said similarity measure is greater than said similarity threshold or said local background color estimate is equivalent to said page background color estimate; g) classifying said pixel of interest as a first-category pixel when said contrast measure is less than a contrast threshold and said local background color estimate is not equivalent to said page background color estimate; h) evaluating a large-text-character condition for said pixel of interest when said contrast measure is not less than said contrast threshold or said local background color estimate is equivalent to said page background color estimate; i) classifying said pixel of interest as a second-category pixel when said large-text-character condition is satisfied; j) computing a dynamic threshold when said large-text-character condition is not satisfied, wherein computing said dynamic threshold comprises; i) calculating a distance between the color of each of said plurality of pixels in said region and said local background color estimate, thereby producing a plurality of color distances; ii) determining the range of said plurality of color distances; iii) adjusting said range by a constant, thereby producing an adjusted range; iv) determining the minimum-value color distance of said plurality of color distances; and v) adding said adjusted range and said minimum-value color distance, thereby producing said dynamic threshold; k) classifying said pixel of interest as a second-category pixel when said similarity measure is greater than said dynamic threshold; and l) classifying said pixel of interest as a first-category pixel when said similarity measure is not greater than said dynamic threshold.
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Specification