Methods and apparatuses for measuring an extent of a group of objects within an image

• US 6,571,006 B1
• Filed: 11/30/1998
• Issued: 05/27/2003
• Est. Priority Date: 11/30/1998
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Montillo, Albert A., Marrion, Cyril C. Jr., Bachelder, Ivan A.
• Primary Examiner(s): Johnson, Timothy M.
• Assistant Examiner(s): CHAWAN, SHEELA C
• Application Number:
  US09/201,412
• Time in Patent Office: 1,639 Days
• Field of Search: 382/146, 382/147, 382/150, 382/168, 382/173, 382/199, 382/218, 382/151, 356/237.1, 356/237.5, 356/601, 378/58
• US Class Current: 382/147
• CPC Class Codes: G06F 18/211 Selection of the most significant subset of features

Abstract

Methods are disclosed that measure the extent of a group of objects within a digital image by comparing signature, representative of the relationship of the objects to one another, against instances of a measured signature at varying positions within the image. The position(s) where the signature(s) vary by a predetermined comparison criterion indicates the extent of the group of objects. It is disclosed that the comparison to a reference signature allows proper identification of measured signatures despite noise in the digital image. A preferred embodiment uses the CALIPER TOOL to generate signatures of edges, where the window of the CALIPER TOOL has a projection axis substantially parallel to the extent being measured. A preferred application is desired wherein the method measure the length of leads in a lead set.

Claims

1. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least one arrangement of the objects relative to one another comprising;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects at the reference position;

detecting edges by projecting the part of the image within the window along the projection axis; and

measuring a reference signature using the edges;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature at a plurality of positions of the window along a direction of the extent by projecting the part of the image within the window along the projection axis;

comparing the reference signature to the measured signature at each of the plurality of positions;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating the extent of the group of objects using the at least one window position.

2. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least one arrangement of the objects relative to one another by placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects at the reference position and measuring a reference signature by projecting the part of the image within the window along the projection axis;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature at a plurality of positions of the window along a direction of the extent by projecting the part of the image within the window along the projection axis;

comparing the reference signature to the measured signature at each of the plurality of positions;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating the difference between the reference window position of the reference signature and the at least one window position of the measured signature to provide the extent of the group of objects.

8. The method of claim 2, wherein the objects are leads on a leaded device.

3. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least one arrangement of the objects relative to one another;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature of the window at a plurality of positions in opposite directions, both the opposite directions being along a direction of the extent, by projecting the part of the image within the window along the projection axis;

comparing the reference signature to the measured signature at each of the plurality of positions;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating the extent of the group of objects using the at least one window position.

4. The method of claim 3, wherein calculating the extent of the group of objects using the at least one window position involves,

calculating the extent as the difference between the at least one window positions of each direction.

5. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least one arrangement of the objects relative to one another, the reference signature having slots;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature at a plurality of positions of the window along a direction of the extent by projecting the part of the image within the window along the projection axis, the measured signature having edges;

comparing the reference signature to the measured signature at each of the plurality of positions by matching a portion of the slots of the reference signature with similarly arranged edges of the measured signature, and disregarding any not similarly arranged edges in the measured signature;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature;

calculating the extent of the group of objects using the at least one window position.

6. The method of claim 5, wherein a number of edges in the measured signature exceeds a number of sides of the group of objects.

7. The method of claim 5, wherein the edges of the measured signature have contrast values and position.

9. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least a number of the objects in the digital image, the reference signature having slots;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature at a plurality of positions of the window along a direction of the extent by projecting the part of the image within the window along the projection axis, the measured signature having edges;

comparing the reference signature to the measured signature at each of the plurality of positions comprising matching a portion of the slots of the reference signature with similarly arranged edges of the measured signature and disregarding any not similarly arranged edges in the measured signature;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating the extent of the group of objects using the at least one window position.

10. A method for measuring an extent of a group of objects within a digital image, the method comprising:

providing a reference signature of the group of objects representative of at least a number of the objects in the digital image;

placing a window extending across at least a portion of the group of objects and having a projection axis substantially parallel to the extent of the group of objects;

measuring a measured signature at a plurality of positions of the window along a direction of the extent by projecting the part of the image within the window along the projection axis;

comparing the reference signature to the measured signature at each of the plurality of positions;

recording at least one window position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating the extent of the group of objects using the at least one window position by returning the extent of the group of objects as the difference between two window positions at which the measured signature differs by a predetermined comparison criteria from the reference signature.

11. An apparatus for measuring an extent of a group of objects within a digital image, the apparatus comprising:

a reference signature of the group of objects representative of the arrangement of the objects relative to one another in the image, the reference signature having slots;

window means having a projection axis positioned substantially parallel to the extent of the group of objects and extending across at least a portion of the group of objects;

measuring means for measuring a measured signature at a plurality of positions of the window means along the direction of the extent by projecting the part of the image within the window means along the projection axis, the measured signature having edges;

comparing means for comparing the reference signature to the measured signature at each of the plurality of positions, the comparing means comprising a matching means for matching a portion of the slots of the reference signature with similarly arranged edges of the measured signature and for disregarding any not similarly positioned edges in the measured signature;

recording at least one window means position at which the measured signature differs by a predetermined comparison criteria from the reference signature; and

calculating means for calculating the extent of the group of objects using the at least one window means position.