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Enhanced Two-Dimensional, Deskewing Algorithm for Document Scanners with Linear CCDs

IP.com Disclosure Number: IPCOM000110791D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Prakash, R: AUTHOR [+3]

Abstract

The misalignment of a document and the lack of orthogonality of a linear CCD with respect to the document transport direction causes skewness and geometric distortion, respectively, in the scanned image. While the conventional techniques help eliminate the skewness due to the former cause, the effects of the latter cause remain uncorrected.

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Enhanced Two-Dimensional, Deskewing Algorithm for Document Scanners
with Linear CCDs

      The misalignment of a document and the lack of orthogonality of
a linear CCD with respect to the document transport direction causes
skewness and geometric distortion, respectively, in the scanned
image.  While the conventional techniques help eliminate the skewness
due to the former cause, the effects of the latter cause remain
uncorrected.

      Both of these errors are corrected by exercising the algorithms
during image extraction, from the stored uncorrected image.

      The first error (document skew) is accomodated for by measuring
the document skew with respect to the x-axis (Figure) and then
extracting the image from the rasterized image buffer.  It is shown
as dots along the document edge.

      The process continues, as each of the rasterized image lines
(parallel to X-axis) is extracted.  The same skew angle is used for
correcting errors along the Y-axis.

      The second error, leading to geometric distortion of the image,
is fixed for a given set of hardware.  While deskewing the image, as
illustrated above, the skew angle along the Y-axis is modified by
this error, i.e., the skew angle is modified by the measure of
misorthognality (fixed for a system ).

The resulting image is free of skew and distortion.