Method utilizing intensity interpolation for measuring edge locations in a high precision machine vision inspection system

• US 20070183666A1
• Filed: 02/08/2006
• Published: 08/09/2007
• Est. Priority Date: 02/08/2006
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Ding, Yuhua
• Granted Patent: US 7,567,713 B2
• Time in Patent Office: Days
• US Class Current: 382/199
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/30164 Workpiece; Machine component
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/12 Edge-based segmentation
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 10/421 by analysing segments intersecting the pattern
• CPC Class Codes: G06V 10/44 Local feature extraction by analysis of parts of the pattern, e.g. by detecting edges, contours, loops, corners, strokes or intersections; Connectivity analysis, e.g. of connected components

Abstract

A method for operating a video tool to perform precision edge detection in an image. The method includes determining estimated image intensity values corresponding to positions along a straight line aligned with a defined scan line orientation. The location of an edge point along the straight line is determined based on the estimated intensity values and their positions along the straight line. The method reduces sub-pixel orientation-dependent variations that may otherwise be present in edge measurements. Intensity values may be estimated by interpolating between nearest neighbor image pixel intensity values. When positions along the straight line are chosen to coincide with a pixel row or column, the interpolating may be linear interpolation between the intensities of just two adjacent pixels.

Claims

1. A method for determining the location of an edge feature in an inspection image of a workpiece acquired by a machine vision inspection system, the method comprising:

a) identifying an edge feature included in the image;

b) defining a scan line orientation to be used for determining the location of at least one edge point of the edge feature;

c) determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation; and

d) determining the location of the edge point along the straight line based on the plurality of estimated image intensity values and their corresponding positions along the straight line.

2. The method of claim 1, wherein determining the plurality of estimated image intensity values comprises estimating the image intensity values using bilinear interpolation.

3. The method of claim 2, wherein for each of the positions along the straight line, the bilinear interpolation is performed utilizing the image intensity values of the four nearest neighbor pixels to the position.

4. The method of claim 1, wherein at least one of the positions along the straight line is determined such that it nominally coincides with either a pixel row or a pixel column.

5. The method of claim 4, wherein when one of the positions along the straight line is determined such that it nominally coincides with a pixel row, then estimating the image intensity value corresponding to that position comprises linear interpolation between the image intensity values of the two nearest neighbor pixels in the same pixel row.

6. The method of claim 4, wherein when one of the positions along the straight line is determined such that it nominally coincides with a pixel column, then estimating the image intensity value corresponding to that position comprises linear interpolation between the image intensity values of the two nearest neighbor pixels in the same pixel column.

7. The method of claim 1, wherein steps a) and b) are performed by configuring a video tool displayed on a display of the image, and steps c) and d) are performed by an edge point locating routine of the video tool, the routine comprising:

instructions that control the machine vision inspection system to perform operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation and that estimate the image intensity values by interpolating between the image intensity values of image pixels that are nearest neighbors for each of the positions along the straight scan line; and

instructions that control the machine vision inspection system to perform operations for determining the location of the edge point along the straight line based on the plurality of estimated image intensity values and their corresponding positions along the straight line.

8. The method of claim 7, wherein identifying an edge feature included in the image comprises positioning an edge-identifying element of a graphical user interface of the video tool on a display of the image.

9. The method of claim 8, wherein the video tool is one of a point tool and a box tool, and defining a scan line orientation to be used for determining the location of at least one edge point of the edge feature comprises orienting a scan line orientation indicating element of a graphical user interface of the video tool on a display of the image.

10. The method of claim 8, wherein:

the video tool is a circle tool;

the edge point locating routine comprises scan line determining instructions that control the machine vision inspection system to perform operations that define the respective orientations of each of a plurality of radially oriented straight scan lines that are distributed at a plurality of angles around the region of interest;

defining a scan line orientation to be used for determining the location of at least one edge point of the edge feature comprises executing the scan line determining instructions; and

the operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation comprise operations that determine a plurality of estimated image intensity values corresponding to positions along each of the plurality of radially oriented straight scan lines.

11. A video tool for determining the location of an edge feature in an inspection image of a workpiece acquired by a machine vision inspection system, the video tool comprising:

a graphical user interface edge-identifying element positionable on a display of the image to identify an edge feature included in the image;

means for defining a scan line orientation to be used for determining the location of at least one edge point of the edge feature; and

an edge point locating routine that comprises;

instructions that control the machine vision inspection system to perform operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation; and

instructions that control the machine vision inspection system to perform operations for determining the location of the edge point along the straight line based on the plurality of estimated image intensity values and their corresponding positions along the straight line.

12. The method of claim 11, wherein the operations for determining the plurality of estimated image intensity values corresponding to positions along a straight line comprise operations that estimate the image intensity values using bilinear interpolation.

13. The method of claim 11, wherein the operations for determining the plurality of estimated image intensity values corresponding to positions along a straight line comprise:

operations that determine at least one of the positions along the straight line such that it nominally coincides with a pixel row; and

value estimating operations such that when one of the positions along the straight line coincides with a pixel row, the value estimating operations estimate the image intensity value corresponding to that position using linear interpolation between the image intensity values of the two nearest neighbor pixels in the same pixel row.

14. The method of claim 11, wherein the operations for determining the plurality of estimated image intensity values corresponding to positions along a straight line comprise:

operations that determine at least one of the positions along the straight line such that it nominally coincides with a pixel column; and

value estimating operations such that when one of the positions along the straight line coincides with a pixel column, the value estimating operations estimate the image intensity value corresponding to that position using linear interpolation between the image intensity values of the two nearest neighbor pixels in the same pixel column.

15. The method of claim 11, wherein:

the video tool is a point tool;

the edge-identifying element comprises at least one of a point tool body and an edge selector;

the means for defining the scan line orientation comprises the point tool body as oriented on the display of the image; and

the operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation comprise operations that determine the straight line such that it is collinear with the point tool body and that estimate the image intensity values by interpolating between the image intensity values of image pixels that are nearest neighbors for each of the positions along the straight line.

16. The method of claim 11, wherein:

the video tool is a box tool;

the edge-identifying element comprises at least one of a region of interest indicator and an edge selector;

the means for defining the scan line orientation comprises at least one of the region of interest indicator as oriented on the display of the image, a box tool orientation indicator as oriented on the display of the image, and a scan line indicator on the display of the image; and

the operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation comprise;

operations that determine a plurality of straight scan lines that are aligned parallel to the defined scan line orientation and distributed within the region of interest; and

operations that determine a plurality of estimated image intensity values corresponding to positions along each of the plurality of straight scan lines and that estimate the image intensity values by interpolating between the image intensity values of image pixels that are nearest neighbors for each of the positions along each straight scan line.

17. The method of claim 11, wherein:

the video tool is a circle tool;

the edge-identifying element comprises at least one of a region of interest indicator and an edge selector;

the means for defining the scan line orientation comprises instructions included in the edge point locating routine that control the machine vision inspection system to perform operations that define the respective orientations of each of a plurality of radially oriented straight scan lines that are distributed at a plurality of angles around the region of interest; and

the operations for determining a plurality of estimated image intensity values corresponding to positions along a straight line that is aligned with the defined scan line orientation comprise operations that determine a plurality of estimated image intensity values corresponding to positions along each of the plurality of radially oriented straight scan lines and that estimate the image intensity values by interpolating between the image intensity values of image pixels that are nearest neighbors for each of the positions along each straight scan line.