Edge contour tracking from a first edge point

• US 5,943,441 A
• Filed: 06/17/1998
• Issued: 08/24/1999
• Est. Priority Date: 12/06/1995
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Michael, David
• Primary Examiner(s): Tran, Phuoc
• Application Number:
  US09/098,801
• Time in Patent Office: 433 Days
• Field of Search: 382/199, 382/205
• US Class Current: 382/199
• CPC Class Codes: G06T 7/13 Edge detection
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation

Abstract

A method and apparatus for finding an edge contour in an image of an object is provided that is robust against object/background misclassification due to non-uniform illumination across an image, while also being computationally efficient, and avoiding the need to select a classification threshold. The invention can be used to partition an image of a scene into object regions and background regions, or foreground regions and background regions, using edge contours found in the image. The invention is particularly useful for analysis of images of back-lit objects. The edge contour is progressively formed by finding a sequence of one-dimensional edge positions, each one-dimensional edge position being determined by processing a set of pixels arranged along at least one imaginary line.

Claims

1. A method for finding a boundary in an image of an object and a background, the method comprising;

progressively forming an edge contour by finding a contiguous sequence of sequentially neighboring interpolated maxima of a first difference taken across the edge contour, each first difference being taken by processing a set of pixels only one pixel wide, and shorter than both the length in pixels and width in pixels of the image.

2. A method for finding an edge contour in an image, the edge contour including a sequence of contour points, the method comprising;

determining the position of a contour point including locating the position of an edge in a one-dimensional gray value signal taken along a first line of a pixel set across the edge contour;

advancing to a next contour point based on each preceding edge so-located; and

returning to determining the position of a contour point.

3. The method of claim 2, wherein locating the position of an edge in a one-dimensional gray value signal includes:

finding an interpolated edge peak.

4. The method of claim 2, wherein said first line of the pixel set across the edge contour is a line parallel to a coordinate axis of the image.

5. The method of claim 2, wherein determining the position of a contour point further includes:

locating the position of an edge in a one-dimensional gray value signal taken along a second line of a second pixel set across the edge contour.

6. The method of claim 5, wherein said second line of the second pixel set is perpendicular to said first line.

7. A method for finding a boundary in an image of an object and a background, the method comprising:

progressively forming an edge contour by finding a contiguous sequence of sequentially neighboring interpolated maxima of an edge signal taken across the edge contour, each edge signal being taken by processing a set of pixels along a line across the edge contour, the set of pixels being of a length that is less than both the width and the length of the image.