High speed three dimensional imaging method

• US 6,147,760 A
• Filed: 08/12/1999
• Issued: 11/14/2000
• Est. Priority Date: 08/30/1994
• Status: Expired due to Term

• Current Assignee: Technest Holdings, Inc. (AccelPath, Inc.)
• Original Assignee: Genex Technologies Incorporated (AccelPath, Inc.)
• Inventors: Geng, Zheng Jason
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US09/372,980
• Time in Patent Office: 460 Days
• Field of Search: 356/3.01, 356/3.02, 356/3.03, 356/3.04, 356/3.06, 356/3.07, 356/375, 356/376
• US Class Current: 356/602
• CPC Class Codes: G01B 11/2509 Color coding
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A three-dimensional (3D) surface profile measurement method and apparatus uses projected energy with a known spatially varying wavelength distribution over the surface of objects in a scene. The varying wavelength of the light corresponds to the angle at which the light is emitted from a light source. Given this correspondence, light reflected from the scene can be identified by wavelength as to angle at which it was emitted. Triangulation can then be used to determine the distance to the point in the scene from which the detected light is reflected. When performed over a number of points on the scene, a three-dimensional profile of the scene can be generated.

Claims

1. An apparatus for determining a distance to each point in a scene so as to generate a three-dimensional profile of said scene, the apparatus comprising:

(a) a color camera for detecting and recording said scene, said camera discriminating a wavelength of light received from said scene for points of said scene;

(b) a light projector for generating light to illuminate said scene for said camera, wherein a wavelength of said light from said light projector varies spatially across said scene such that only light of a particular wavelength is emitted by said light projector at a predetermined angle with respect to a line between said camera and said light projector;

wherein said apparatus determines a distance to said points of said scene based on distance between said light projector and said camera, the wavelength of received light associated with that point by said camera and an angle corresponding to emission of that wavelength by said light projector.

2. The apparatus of claim 1, wherein said light projector comprises a variable wavelength filter for causing said spatial variation in said light from said light projector.

3. The apparatus of claim 2, wherein said variable wavelength filter comprises a substantially rectilinear transparent plate through which light from said light projector is transmitted, and wherein at least one surface of said plate is coated with a coating having a color which gradually varies over said surface of said plate.

4. The apparatus of claim 3, wherein a wavelength of said coating at any particular distance from an edge of said filter is linearly proportional to said distance from said edge of said filter thereby providing an efficient means of generating a structured light spectrum without the necessity for any moving parts.

5. The apparatus of claim 2, wherein said variable wavelength filter has a color spectrum within the visible light region and one edge of the filter corresponds to a shortest wavelength in the blue range of the visible spectrum and the opposite edge corresponds to a longest wavelength in the red range of the visible spectrum.

6. The apparatus of claim 2, wherein said light projector further comprises a cylindrical lens through which light is dispersed to shine through said filter.

7. The apparatus of claim 1, further comprising a processor for determining said distance to points of said scene based on said distance between said light projector and said camera, the wavelength of received light associated with that point by said camera and an angle corresponding to emission of that wavelength by said light projector.

8. The apparatus of claim 7, wherein said processor is integrated with said color camera.

9. The apparatus of claim 7, wherein said processor has a look-up table that lists said correspondence between wavelengths of said light and angles of light emission with respect to a line between said camera and said light projector.

10. An method for determining a distance to points in a scene so as to generate a three-dimensional profile of said scene, the apparatus comprising:

(a) generating light to illuminate said scene, wherein a wavelength of said light varies spatially across said scene such that only light of a particular wavelength illuminates said scene at a predetermined angle with respect to a line between a camera and a source of said light;

(b) detecting and recording said scene with said camera, and discriminating, with said camera, a wavelength of light received from said scene for points of said scene;

(c) determining a distance to said points of said scene based on distance between said light source and said camera, the wavelength of received light associated with that point by said camera and an angle corresponding to emission of that wavelength by said light source.

11. The method of claim 10, further comprising causing said spatial variation in said light using a variable wavelength at said light source.

12. The method of claim 10, wherein said step of determining further comprises accessing a look-up table that lists said correspondence between wavelengths of said light and angles of light emission with respect to a line between said camera and said light source.

13. The method of claim 10, further comprising compensating for ambient light conditions during said detecting and recording with said camera.

14. The method of claim 13, wherein said compensating for ambient light conditions further comprising:

imaging said scene under said ambient light conditions prior to said step of generating light; and

subtracting an image of said scene under ambient light conditions from a subsequent recording taken in said detecting and recording step to eliminate any effect of said ambient light conditions in said subsequent recording.

15. A method of color ranging to capture a full frame of 3D image data of a scene-to-be profiled at the frame rate of a color camera comprising the steps of:

illuminating said scene from a light projector which generates a fan of light, projecting said fan of light through a variable wavelength filter means whereby said scene is illuminated by projected light energy which has a known spatially varying wavelength spectrum whereby points on the scene are illuminated with predetermined radiation energy having a unique wavelength; and

detecting said spectrum of reflected light by said color camera whereby the color spectrum detected for pixels of said color camera has a one-to-one correspondence with the projection angle of the plane of light due to a predetermined geometry of the illuminating plane of light and the variable wavelength filter means whereby the detected color spectrum provides an angular measurement for said points on the scene thereby facilitating a triangulation calculation of the 3D range data.

16. The method of claim 15, wherein a visible range variable wavelength filter means is utilized and the color spectrum of each pixel of the detected image is determined by the proportion of red, green, and blue components of said detected color spectrum for each pixel.

17. An apparatus for determining a distance to each point in a scene so as to generate a three-dimensional profile of said scene, the apparatus comprising:

(a) means for imaging said scene and for discriminating a wavelength of light received from said scene for points of said scene;

(b) means for generating light to illuminate said scene, wherein a wavelength of said light varies spatially across said scene such that only light of a particular wavelength is emitted at a predetermined angle with respect to a line between said light generating means and said imaging means;

(c) means for determining a distance to said points of said scene based on distance between said light generating means and said imaging means, the wavelength of received light associated with that point by said imaging means and an angle corresponding to emission of that wavelength by said light generating means.

18. The apparatus of claim 17, wherein said light generating means comprises a variable wavelength filter means for causing said spatial variation in said light from said light generating means.

19. The apparatus of claim 18, wherein said variable wavelength filter means comprises a substantially rectilinear transparent plate through which light from said light projector is transmitted, and wherein at least one surface of said plate is coated with a color coating means having a color which gradually varies over said surface of said plate.

20. The apparatus of claim 18, wherein said light generating means further comprises a means for evenly dispersing light from a light source means to shine through said filter means.