Browse Prior Art Database

Projection Method for Edge and Corner Location for Image Extraction

IP.com Disclosure Number: IPCOM000115051D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 76K

Publishing Venue

IBM

Related People

Eagle, BC: AUTHOR [+2]

Abstract

A method for locating a rectangle enclosing a document within an image is disclosed. If the document is skewed, the enclosing rectangle is rotated to match it.

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This is the abbreviated version, containing approximately 53% of the total text.

Projection Method for Edge and Corner Location for Image Extraction

      A method for locating a rectangle enclosing a document within
an image is disclosed.  If the document is skewed, the enclosing
rectangle is rotated to match it.

      An image of a document is made up of pixels that are part of
the document and background pixels that are located outside the
document.  Documents are assumed to be white; the backgrounds are
dark.  In the following description, the gray-scale values for white
pixels are greater than the gray-scale values for black pixels.
  1.  Establish a document gray-scale threshold value.  Any pixel
with
       a gray-scale value greater than this threshold is assumed to
be
       part of the document.
  2.  Find the top and bottom boundaries of the document by examining
       each column of pixels within the image.  For each column, find
       the locations of the first and last pixels with gray-scale
values
       exceeding the threshold.  The top and bottom boundary
locations
       form an outline of the desired image as shown in Fig. 1.
  3.  Use the top and bottom boundary locations to find the height of
       the document by subtracting the bottom locations from the
       corresponding top locations to form an array of document
heights.
       The array of heights forms the projection shown in Fig. 2.
  4.  Establish a threshold to separate the "plateau" of the height
       curve from the sloped sides as shown in Fig. 2.
  5.  Find the line that forms the top edge of the document.  The
line
       is defined by one of its points and its slope.
      o  Choose a point on the top edge with a horizontal position
          near the center of the plateau.
      o  Calculate the slope of the line using the coordinates of two
          points with horizontal positions near the ends of the
plateau.
  6.  Find the line that for...