Method and apparatus for identifying the rotation angle and bounding rectangle of a digitized form
First Claim
1. A method of processing an image represented by a plurality of pixel values, each pixel value corresponding to a pixel element, the method comprising:
- operating a processor in a computer system to generate for each of a plurality of first bands of pixel values in said image, a first set of first histogram values, said first bands extending in a first direction, each first histogram value corresponding to a set of pixel values extending in a second direction perpendicular to said first direction; and
analyzing at least some of the first set of histogram values to determine for each analyzed first set of histogram values a location of a first image edge and a first confidence value corresponding to the determined first image edge location.
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Abstract
Methods and apparatus for determining the skew angle of a digitized form scanned at an angle to the original page are described. The method determines a rotation angle and a boundary rectangle of best fit. Sections of the digital image in the form of thin strips are examined for the boundary between the page and the region of the scanned image beyond the original page. The Hough transform is employed to determined candidate edge line segments for the page from the sets of perimeter points. These line segments are then combined to select the best rectangle enclosing the page, from which the skew angle is determined. The algorithm also determines a rotated bounding box enclosing the page. An innovation of the invention is the use of fuzzy logic, whereby several candidates for perimeter points, candidate edges, and bounding rectangles are determined in each step of the computation with associated confidence values and the final skew angle is selected by choosing the bounding rectangle with the highest confidence values.
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Citations
31 Claims
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1. A method of processing an image represented by a plurality of pixel values, each pixel value corresponding to a pixel element, the method comprising:
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operating a processor in a computer system to generate for each of a plurality of first bands of pixel values in said image, a first set of first histogram values, said first bands extending in a first direction, each first histogram value corresponding to a set of pixel values extending in a second direction perpendicular to said first direction; and analyzing at least some of the first set of histogram values to determine for each analyzed first set of histogram values a location of a first image edge and a first confidence value corresponding to the determined first image edge location. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method of processing image data, method comprising:
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operating a processor in a computer system to select, from a set of possible edge lines including at least said set of eight possible edge lines, a set of four possible edges lines as a function of which combination of edge lines in said set of possible edge lines is determined to most probably correspond to the shape of a scanned image; and performing one of;
i) outputting information indicating the selected set of four edge lines, ii) storing information indicating the selected set of four edge lines and iii) using the selected set of four edge lines in an image processing operation. - View Dependent Claims (25, 26, 27, 28, 29)
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30. An apparatus for processing an image represented by a plurality of pixel values, each pixel value corresponding to a pixel element, the apparatus comprising:
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a processor; and a memory including; means for controlling the processor to generate, for each of a plurality of first bands of pixel values in said image, a first set of first histogram values, said first bands extending in a first direction, each first histogram value corresponding to a set of pixel values extending in a second direction perpendicular to said first direction; and means for controlling the processor to analyze at least some of the first set of histogram values to determine for each analyzed first set of histogram values a location of a first image edge and a first confidence value corresponding to the determined first image edge location.
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31. A non-transitory machine readable medium including machine executable instructions which, when executed control a processor to implement a method of processing an image represented by a plurality of pixel values, each pixel value corresponding to a pixel element, the method comprising the steps of:
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generating for each of a plurality of first bands of pixel values in said image, a first set of first histogram values, said first bands extending in a first direction, each first histogram value corresponding to a set of pixel values extending in a second direction perpendicular to said first direction; and analyzing at least some of the first set of histogram values to determine for each analyzed first set of histogram values a location of a first image edge and a first confidence value corresponding to the determined first image edge location.
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Specification