Object imaging device and method using line striping

• US 5,753,931 A
• Filed: 07/13/1995
• Issued: 05/19/1998
• Est. Priority Date: 07/13/1995
• Status: Expired due to Term

• Current Assignee: Nike, Inc., Nike International Ltd. (Nike, Inc.), Prosthetics Research Study, Inc.
• Original Assignee: Nike, Inc.
• Inventors: Birdwell, Kenneth, Boone, David A., Kilgore, Bruce J., Borchers, Robert E., Rosenthal, Eric D.
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US08/501,869
• Time in Patent Office: 1,041 Days
• Field of Search: 250/208.1, 250/559.05, 250/559.06, 250/559.07, 250/559.08, 250/559.19, 250/559.22, 250/559.24, 250/559.26, 250/216, 250/234, 250/235 , 250/236, 356/376, 33/3 R, 33/6, 33/511, 33/512, 33/515, 128/779, 382/255, 382/266, 382/286, 382/321, 382/128, 382/111
• US Class Current: 250/559.22
• CPC Class Codes: A43D 1/025 comprising optical means, e.g. mirrors, photo-electric cells, for measuring or inspecting feet
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A device and method is provided for quickly and accurately obtaining surface contour information from an object without the need for precisely aligning and calibrating mechanical structures or optics elements, and without moving parts. In various embodiments, the invention includes steps of projecting a plurality of parallel planes of laser light through a transparent plate onto a surface of the object, receiving a reflection from the object in a digital camera, and performing image processing on the reflected image to reconstruct the three-dimensional surface of the object therefrom. The image processing includes steps of subtracting an image of the object in its non-illuminated state from an image of the object illuminated by the plurality of parallel planes of light, performing a thresholding operation on the subtracted image, and generating a line array containing lines having curvature deformations due to surface deviations on the object. The line array is transformed into a three-dimensional image by applying a transformation matrix previously obtained by processing an image of a calibration gauge placed on the transparent plate. Both single-image and multiple-image projection systems may be implemented.

Claims

1. Apparatus for measuring the surface geometry of an object, comprising:

a housing having a transparent plate;

light projection means, disposed in the housing, for generating and simultaneously projecting a plurality of parallel lines of light onto the object through the transparent plate;

image capture means, disposed to receive a reflection of the projected plurality of parallel lines from the object, for capturing the reflection and storing a digital representation thereof into a computer memory; and

means for controlling the light projection means and the image capture means to separately capture first and second images, the first image comprising an image of the object with the light projection means activated to produce the plurality of parallel lines of light, the second image comprising an image of the object with the light projection means deactivated so that the object is illuminated only with ambient light.

2. The apparatus of claim 1, further comprising image processing and reconstruction means, coupled to the image capture means, for generating a three-dimensional representation of a surface of the object by transforming the digital representation using data generated from a calibration gauge.

3. The apparatus of claim 2, wherein the image processing and reconstruction means comprises:

means for producing a subtracted image by subtracting the first and second images; and

means for performing a sub-pixel interpolation operation on the subtracted image in order to locate center points of each of a plurality of image lines in the subtracted image, and producing thereby a line array comprising the center points.

4. The apparatus of claim 2, wherein the image processing and reconstruction means comprises:

means for producing a line array from the digital representation, the line array comprising a plurality of image lines each corresponding to one of the parallel lines of light; and

means for generating the three-dimensional representation by applying 2-D to 3-D transformation data to the line array.

5. The apparatus according to claim 2, further comprising means for rendering the three-dimensional representation on a computer display.

6. The apparatus of claim 2, wherein the image processing and reconstruction means comprises:

means for producing a subtracted image by subtracting the first and second images;

means for performing a thresholding operation on the subtracted image and producing a thresholded image; and

means for generating a line array of pixels corresponding to lines reflected off the object from the thresholded image.

7. The apparatus of claim 6, wherein the image processing and reconstruction means comprises means for transforming the line array of pixels into the three-dimensional image by applying a transformation matrix created by capturing an image of a calibration gauge placed on the transparent plate.

8. The apparatus of claim 7, further comprising means for resampling the three-dimensional image according to a user-specified frequency and storing the result thereof into a data structure.

9. The apparatus of claim 1, wherein the housing comprises a step for allowing a person to climb atop the housing, wherein the transparent plate is disposed in the top of the housing and is of a size selected to encompass a human foot, and wherein the light projection means projects approximately 66 parallel lines of light through the transparent plate.

10. The apparatus of claim 1, wherein the light projection means comprises:

a laser for generating a beam of coherent light;

beamsplitting means, disposed in an optical path of the laser, for splitting the beam of coherent light into the plurality of parallel lines of light;

a lens, disposed in an optical path of the beamsplitting means, for focusing the plurality of parallel lines of light; and

a mirror, disposed in an optical path of the lens, for reflecting the focused plurality of parallel lines of light toward the transparent plate.

11. The apparatus of claim 1,

wherein the light projection means comprises a first light source for generating a first portion of the plurality of parallel lines of light and a second light source for generating a second portion of the plurality of parallel lines of light;

and

wherein the image capture means comprises a first camera for capturing a first portion of the reflection and a second camera for capturing a second portion of the reflection.

12. The apparatus of claim 1, further comprising a fan coupled to the housing and disposed to blow a stream of air across the transparent plate to prevent condensation from forming thereon.

13. The apparatus of claim 1, further comprising a calibration gauge, having a shape adapted to be placed on the transparent plate, wherein the image capture means captures and stores a digital representation of a reflection of the calibration gauge.

14. A method of measuring the surface geometry of an object, comprising the steps of:

(1) placing the object onto a transparent plate;

(2) generating and simultaneously projecting a plurality of parallel lines of light onto the object through the transparent plate;

(3) capturing an image corresponding to a reflection of the projected plurality of parallel lines from the object; and

(4) storing a digital representation of the captured image into a computer memory by separately capturing first and second images, the first image comprising an image of the object while illuminated by the plurality of parallel planes of light, the second image comprising an image of the object illuminated with only ambient light.

15. The method of claim 14, further comprising the step of blowing a stream of air across the transparent plate to prevent condensation from forming thereon.

16. The method of claim 15, further comprising the step of:

(5) generating a three-dimensional representation of a surface of the object by transforming the digital representation using data generated from a calibration gauge.

17. The method of claim 16, wherein step (5) comprises the steps of:

(a) producing a subtracted image by subtracting the first and second images; and

(b) performing a sub-pixel interpolation operation on the subtracted image in order to locate center points of each of a plurality of image lines in the subtracted image, and producing thereby a line array comprising the center points.

18. The method of claim 16, wherein step (5) comprises the steps of:

(a) producing a line array from the digital representation, the line array comprising a plurality of image lines each corresponding to one of the parallel lines of light; and

(b) generating the three-dimensional representation by applying 2-D to 3-D transformation data to the line array.

19. The method of claim 16, further comprising the step of rendering the three-dimensional representation on a computer display.

20. The method of claim 16, wherein step (5) comprises the steps of:

(a) producing a subtracted image by subtracting the first and second images;

(b) performing a thresholding operation on the subtracted image and producing a thresholded image; and

(c) generating a line array of pixels corresponding to lines reflected off the object from the thresholded image.

21. The method of claim 20, further comprising the step of:

(d) transforming the line array of pixels into the three-dimensional image by applying a transformation matrix created by capturing an image of a calibration gauge placed on the transparent plate.

22. The method of claim 21, further comprising the step of resampling the three-dimensional image according to a user-specified frequency and storing the result thereof into a data structure.

23. The method of claim 21, further comprising the step of exporting the three-dimensional image in a CAD/CAM format.

24. The method of claim 21, further comprising the step of modifying the three-dimensional image in accordance with shoe insole parameters.

25. The method of claim 14, further comprising the step of providing a housing having a step for allowing a person to climb atop the housing, and

wherein step (1) comprises the step of using a transparent plate disposed in the top of the housing of a size adapted to encompass a human foot, and

wherein step (2) comprises the step of projecting approximately 66 parallel lines of light through the transparent plate.

26. The method of claim 14 wherein step (2) comprises the steps of:

(a) using a laser to generate a beam of coherent light;

(b) using a beamsplitter, disposed in an optical path of the laser, for splitting the beam of coherent light into the plurality of parallel lines of light;

(c) using a lens, disposed in an optical path of the beamsplitter, for focusing the plurality of parallel lines of light; and

(d) using a mirror, disposed in an optical path of the lens, for reflecting the focused plurality of parallel lines of light toward the transparent plate.

27. The method of claim 14,

wherein step (2) comprises the step of using a first light source for generating a first portion of the plurality of parallel lines of light and a second light source for generating a second portion of the plurality of parallel lines of light;

and

wherein step (3) comprises the step of using a first camera for capturing a first portion of the reflection and a second camera for capturing a second portion of the reflection.

28. The method of claim 14, further comprising the steps of, prior to step (1):

(a) placing a calibration gauge onto the transparent plate;

(b) capturing an image of the calibration gauge while illuminated by a plurality of parallel lines of light; and

(c) processing the captured image of the calibration gauge to produce a transformation matrix used for converting the digital representation stored in step (4) into a three-dimensional representation of a surface of the object.

29. The method of claim 14, wherein step (1) comprises the step of placing a human foot onto the transparent plate.

30. Apparatus for measuring the surface geometry of an object, comprising:

a housing having a transparent plate;

a light source which generates a beam of light;

a beamsplitter, disposed between the light source and the transparent plate, which splits the beam of light into a plurality of parallel lines of light which are transmitted through the transparent plate and reflected onto the surface of an object placed on the transparent plate;

a camera positioned to receive a reflection of the surface of the object including the parallel lines of light as reflected from the surface of the object;

a light control circuit coupled to the light source which alternately energizes and de-energizes the light source to alternately illuminate and darken the object, and creating thereby a first illuminated image of the object including the reflected parallel lines of light and a second non-illuminated image of the object; and

a computer, coupled to the camera, which receives and stores the first illuminated image and the second non-illuminated image of the object from the camera, generates a subtracted image comprising a difference between the first illuminated image and the second non-illuminated image, and converts the subtracted image into a data structure representing height information.

31. The apparatus of claim 30, wherein the computer converts the subtracted image into the data structure by segregating portions of the subtracted image into contiguous line segments and reconstructing height information from the contiguous line segments by applying a transformation matrix which incorporates calibration data previously generated through the use of a three dimensional calibration gauge.

32. The apparatus of claim 30, wherein the computer performs a sub-pixel interpolation operation on the subtracted image and generates therefrom a line array comprising center points for a plurality of image lines, each image line corresponding to one of the plurality of parallel lines projected onto the surface of the object.

33. The apparatus of claim 30, wherein the light source comprises a laser;

and wherein the beamsplitter comprises a diffraction grating.

34. The apparatus of claim 30, wherein the light control circuit is coupled to the computer, wherein the computer controls the light control circuit to alternately energize and de-energize the light source in synchronization with successive frames of data captured by the camera.