Video measurement system with automatic calibration and distortion correction

• US 5,070,401 A
• Filed: 04/09/1990
• Issued: 12/03/1991
• Est. Priority Date: 04/09/1990
• Status: Expired due to Term

• Current Assignee: GE Inspection Technologies LP (General Electric Company)
• Original Assignee: Welch Allyn Incorporated
• Inventors: Salvati, Jon R., Lia, Raymond A.
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US07/506,175
• Time in Patent Office: 603 Days
• Field of Search: 358/98, 358/107, 364/560, 364/561, 364/562, 364/563
• US Class Current: 348/141
• CPC Class Codes: G01B 11/024 by means of diode-array scanning
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10068 Endoscopic image
• CPC Class Codes: G06T 7/60 Analysis of geometric attributes
• CPC Class Codes: H04N 23/555 for picking-up images in sites, inaccessible due to their dimensions or hazardous conditions, e.g. endoscopes or borescopes

Abstract

An electronic video measurement system for measuring three dimensional parameters of objects viewed by a two dimensional video image pickup. A borescope is provided in which the measurements are corrected for calibration, distortion, lens magnification, and system architecture. Programs and algorithms are provided for calculating various parameters of an object being viewed, including slant lengths and depths without the need for a scale positioned next to the object being measured.

Claims

1. In a borescope having an elongated insertion tube for viewing inaccessible objects and a video image pickup in the distal end thereof for producing a video image for viewing on a video display the method of measuring the size of the object being viewed by determining the location of a known supplementary image relative to said object being viewed, including the steps of:

projecting a known supplementary images into the object to be measured;

detecting said supplementary and object images;

displaying said detected supplementary and object images on a video display;

electronically counting the number of pixels in the video display screen between an initial point and the supplementary image location to determine object distance;

electronically counting the number of pixels in the video display between a first and second location on the object to be measured;

applying pixel by pixel calibration and distortion correction factors to the pixel counting steps;

calculating and displaying on a video display the actual dimension represented by the number of pixels counted in the counting steps corrected for calibration, distortion and object distance.

2. In a system for viewing objects having a video image pick-up and display, the method of measuring characteristics of the object being viewed which comprises the steps of:

projecting an image with at least one known characteristic on the object to be viewed;

causing said known characteristic to vary in proportion to the distance the object to be viewed is from the video image pick-up;

detecting the object image and the known characteristic image;

displaying the detected images on a video display;

measuring the variation of the known characteristic of the created image to determine object distance;

measuring a desired characteristic of the object being viewed;

creating a table of calibration and correction factors for the video pick-up and display;

calculating a corrected measurement of the desired characteristic of the object being viewed using said table of calibration and correcting factors and the created image variation measurement; and

displaying the calculated result to indicate the measurement of the characteristic of the object being viewed.

3. The method of claim 2 further defined by electronically measuring the variation in the known characteristics of the created image to determine object distance;

electronically applying a bit by bit mapped overlay to the video display corrected for calibration and distortion errors;

electronically measuring the desired characteristic of the object being viewed; and

electronically calculating a corrected characteristic measurement of the object being measured.

4. In a system for measuring dimensions of an object being viewed with a video borescope having a video image pick-up and display, the method of electronically determining the actual physical dimensions of the object which is being viewed including the steps of:

a.) creating a pixel by pixel set of calibration and distortion correction factors for a video image pick-up video display system;

b.) creating a bit mapped information overlay on a one for one pixel basis for the video display to display various information on the display;

c.) creating a known object distance image in the borescope illumination system and projecting it into the field of view thereof so as to fall on the object to be measured;

d.) counting pixels to determine the location of said object distance image on the object being viewed to determine the video image pickup system magnification for the object being viewed;

e.) counting the number of pixels between first and second locations on the object being viewed;

f.) combining the data obtained in the foregoing steps with the video information from the borescope;

g.) calculating the corrected distance between said first and second locations on the object being viewed for the magnification, calibration and distortion factors determined in steps a) through d) for the first and second locations on the object being viewed.

5. The method of claim 4 further defined by counting the pixels in X and Y coordinate directions for said first and second locations;

determining the magnification for each of said first and second locations on the objects being viewed; and

calculating the true distance between said first and second locations from the projected X-Y distance and the X-Y depth.

6. In a system for viewing objects with a video image pickup and displaying them on a video display, the method of measuring three dimensional characteristic of an object being viewed comprising the steps of:

illuminating the object to be viewed;

creating a shadow in said illumination that is displaced across one dimension of the video display in proportion to the object distance from the video image pickup;

positioning the object to be measured and the video image pickup so that the object lies within said shadow;

measuring the object distance of two spaced apart points on the object to be measured while positioned within said shadow by measuring the displacement of said shadow at the respective two points;

measuring the apparent distance between the two spaced apart points as shown on the video display; and

calculating the actual distance between the two points on the object by the difference in object distance obtained from the shadow measurement, the measured apparent distance and the geometry of the video image pickup device.

7. The method of claim 6 further defined by correcting the measurements of the two spaced apart for distortion due to the video image pickup system and the video display to provide a true distance measurement.

8. In a system for viewing objects with a video image pickup and displaying them on a video display according to claim 6 further comprising:

measuring the X and Y coordinates of two spaced apart points on the object to be measured;

measuring the Z coordinate of the two spaced apart points on the object to be measured by determining the object distance of the two points from the displacement of the shadow image; and

calculating the straight line distance between the two points from the measured x y z coordinates of the points.

9. The method of claim 6 further defined by making the measurements of the two spaced apart points by counting the number of pixels on the video display between a zero index point and said two spaced apart points.

10. The method of claim 9 further defined by mapping the configuration of the object being measured by measuring the object distance of a plurality of points on the object to be measured located within said shadow.

11. In a system for viewing objects having a video image pick-up and display, the method of measuring characteristics of the object being viewed which comprises the steps of;

creating first and second images on the object to be viewed, each image having at least one known characteristic

causing a first known characteristic of said first image to vary in proportion to the distance the object to be viewed is from the video image pick-up;

causing a second known characteristic of said first image to vary in proportion to a first angle of the plane of the image to the optical axis;

causing a first known characteristic of said second image to vary in proportion to a second angle of the plane of the image to the optical axis;

detecting the object image and the known characteristic image;

displaying the detected images on a video display;

measuring the variation of the known characteristics of the created images to determine object distance and plane angles;

calculating the measurement of a desired characteristic of the object being viewed using the created image variation measurements; and

displaying the calculated result to indicate the measurement of the characteristic of the object being viewed.

12. In a system for viewing objects having a video image pick-up and display, the method of measuring characteristics of the object being viewed which comprises the steps of:

illuminating the object to be viewed;

creating an image on the object to be viewed with at least two known characteristics;

causing said first known characteristic to vary in proportion to the distance the object to be viewed is from the video image pick-up;

causing said second known characteristic to vary in proportion to the angle of the plane, in which the object being viewed lies, to the optical axis of the system;

detecting the object image and the known characteristics images;

displaying the detected images on a video display;

measuring the variation of the known characteristics of the created images to determine object distance and plane angle;

measuring a desired characteristic of the object being viewed;

calculating a corrected measurement of the desired characteristic of the object being viewed using the determined object distance and plane angle

whereby an accurate measurement can be made of an object lying in planes other than at right angles to the optical axis of the system.

13. The method of claim 12 further defined by creating a primary and secondary shadow line image on the object to be viewed, and varying the displacement of the primary shadow in proportion to the object distance and varying the displacement of the secondary shadow relative to the primary shadow in proportion to one axis angle of the object plane and varying the angle of the shadow lines in proportion to a second axis angle of the object plane.

14. An apparatus for measuring the dimensions of an object being viewed on a video display of a video image pickup system which comprises:

a video system having an illumination source for illuminating the object to be viewed, and a video image sensor operatively associated therewith to detect an image of the object illuminated;

means for creating an image of known characteristics in the illumination source;

means for measuring at least one of the characteristics of said known image when projected on said object to be viewed;

data storage means for storing calibration and distortion correction information for the video image sensor;

video display means operatively connected to said video image sensor;

video display overlay generator means operatively connected to said video display means;

computer CPU means operatively connected to said data storage means and said video overlay generator means for counting pixels on the video display and for calculating corrected pixel dimensional information for said counted pixel information and displaying same on the video display whereby dimensional information about the object being viewed can be determined and displayed.

15. Apparatus as described in claim 14 wherein said video system is a video borescope having an insertion tube with the illumination source and video image sensor positioned in the distal end thereof.

16. In a system for viewing objects having a video image sensor and video display, apparatus for measuring characteristics of the object being viewed which comprises:

means for creating two images with at least one known characteristic each on the object to be viewed;

said image creating means causing at least one of said known characteristics to vary in proportion to the distance the object to be viewed is from the video image pick-up;

video sensor means for detecting the object image and the known characteristic image;

a video display for viewing the detected images;

means for measuring the variation of the known characteristics of the created images to determine object plane;

means for measuring a desired characteristic of the object being viewed;

computer means for calculating a corrected measurement of the desired characteristic of the object being viewed in accordance with the measured variation of the known characteristics.

17. Apparatus as described in claim 16 wherein said means for measuring the object characteristics includes means for counting pixels on the video display between selected points on the object.

18. Apparatus as described in claim 16 wherein said means for creating an image includes means for illuminating the object to be viewed and a pair of spaced apart shadow bars mounted in said illuminating means to project a pair of shadow lines on the object to be viewed.

19. Apparatus as described in claim 18 wherein said shadow bars are mounted off center from the optical axis of said illumination means whereby the shadows created will be displaced in one direction in proportion to the object distance and the spacing between the bars will vary relative to a first angle of the plane of the object to the optical axis.

20. Apparatus as described in claim 19 wherein the shadow bars are mounted so that the angle of the shadow lines created on the object to be viewed will vary in the video display in proportion to a second angle of the plane of the object being viewed relative to the optical axis.