EP0431962A2
Expired / Lapsed
EP
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Method and apparatus for identification of document skew
Assignee: Xerox Corp
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Filing: 1990-12-07
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Granted: —
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Expires: 2010-12-07
Abstract
Abstract A method and apparatus for identifying and correcting for document skew. Lines of a bitmap are scanned and a variance in the number of ON (or OFF) pixels as a function of angle of rotation is calculated (4, 6, 8). Skew of the original document occurs when the variance is a maximum (10).
Inventors
- 👤 Dan S. Bloomberg
- 👤 Gary E. Kopec
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-30 23:26
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/387; H04N1/3877; H04N1/3878; G; G06; G06T; G06T7/00; G06T7/70; G06V; G06V30/00; G06V30/10; G06V30/14; G06V30/146; G06V30/1475; G06V30/1478
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
65 words
A method of determining skew of an image in a digital processing means comprising the steps of determining (4,6,8) a variance either in a number of ON pixels or in a number of OFF pixels in at least one scanline of said image as a function of document rotation angle, and locating (10) the document rotation angle at which said variance is substantially a maximum.
Claim 2
Dependent Claim
16 words
A method as claimed in claim 1, preceded by the step (2) of reducing said image.
Claim 3
Dependent Claim
56 words
A method as claimed in claim 1 or claim 2, wherein said variance is calculated by an equation of the form: N where: N is a number of lines; p is a real number greater than 1; n is the number of the said pixels in a line; and i is a counter for the lines.
Claim 4
Dependent Claim
12 words
A method as claimed in claim 3, wherein p is about 2.
Claim 5
Independent Claim
27 words
A method as claimed in any one of the preceding claims, wherein substantially all of the scanlines in a document are included the determination of said variance.
Claim 6
Independent Claim
24 words
A method as claimed in any one of the preceding claims, wherein document rotation angles are simulated by a vertical shear of said image.
Claim 7
Independent Claim
34 words
A method as claimed in any one of the preceding claims, and further comprising the step (12) of rotating said image by the said located angle so as to produce a deskewed document image.
Claim 8
Dependent Claim
20 words
A digital image processing device programmed to carry out a method as claimed in any one of the preceding claims.
Claim 9
Dependent Claim
103 words
An optical character recognition system comprising: a) input means for inputting an image of a document; b) deskewing means comprising: i) means for simulating rotation of said image from at least a first skew angle to a second skew angle; ii) means for calculating variance of a number of ON pixels in a scanline of said image at each of said skew angles; and iii) means for rotating said image to about an angle which substantially maximizes said variance to produce a deskewed image; c) means for identifying characters in said deskewed image; and d) means for outputting said characters in said image.
Claim 10
Dependent Claim
97 words
Apparatus for copying a document comprising: a) input means for inputting an image of a document; b) deskewing means comprising: i) means for simulating rotation of said image from at least a first skew angle to a second skew angle; ii) means for calculating variance of a number of ON pixels in a scanline of said image at each of said skew angles; and iii) means for rotating said image to about an angle which substantially maximizes said variance to produce a deskewed image of said document; c) means for outputting said deskewed image of said document.
References Cited (Backward Citations)
No citation records indexed.
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