Multi spectral imaging system

• US 5,900,942 A
• Filed: 09/26/1997
• Issued: 05/04/1999
• Est. Priority Date: 09/26/1997
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Spiering, Bruce A.
• Primary Examiner(s): Hantis, K. P.
• Application Number:
  US08/938,300
• Time in Patent Office: 585 Days
• Field of Search: 356/399-401, 356/435, 348/188, 348/263, 348/189-192, 348/94-95, 348/92, 348/133.1, 348/176, 348/33, 382/294-297, 359/618, 359/754
• US Class Current: 356/400
• CPC Class Codes: G01J 3/2823 Imaging spectrometer

Abstract

An optical imaging system provides automatic co-registration of a plurality of multi spectral images of an object which are generated by a plurality of video cameras or other optical detectors. The imaging system includes a modular assembly of beam splitters, lens tubes, camera lenses and wavelength selective filters which facilitate easy reconfiguration and adjustment of the system for various applications. A primary lens assembly generates a real image of an object to be imaged on a reticle which is positioned at a fixed length from a beam splitter assembly. The beam splitter assembly separates a collimated image beam received from the reticle into multiple image beams, each of which is projected onto a corresponding one of a plurality of video cameras. The lens tubes which connect the beam splitter assembly to the cameras are adjustable in length to provide automatic co-registration of the images generated by each camera.

Claims

1. An imaging system for generating automatically co-registered images of an object comprising:

a) a lens assembly for forming a real image of an object at a focal point;

b) a collimating lens for receiving said real image from said focal point, and generating a collimated image beam;

c) a beam splitter assembly positioned to receive said collimated image beam, and split said collimated image beam into at least first and second image beams;

d) first and second tubes having first ends attached to said beam splitter assembly, and having second ends;

e) first and second optical imaging devices attached, one each, to said second ends of said first and second tubes, respectively, for receiving said first and second image beams, respectively; and

f) means for adjusting the lengths of said first and second tubes so that the images received by said first and second optical imaging devices are co-registered with one another.

2. The system of claim 1, further comprising a first wavelength selective filter disposed in a path of said first image beam and a second wavelength selective filter disposed in a path of said second image beam, for selectively filtering the images received by said first and second optical imaging devices, respectively.

3. The system of claim 1, wherein said beam splitter assembly further comprises:

1) a first beam splitter positioned to receive said collimated image beam, and split said collimated image beam into a transmitted image beam, and a reflected image beam; and

2) a fold mirror positioned to receive said reflected image beam, and form a twice reflected image beam;

wherein, said transmitted image beam and said twice reflected image beam are projected through said first and second tubes, respectively, and comprise said first and second image beams, respectively.

4. The system of claim 3, wherein said beam splitter assembly comprises a modular assembly of a plurality of cubes which are connected to one another by at least one coupling, with said first beam splitter being disposed in a first of said cubes, and said fold mirror being disposed in a second of said cubes.

5. The system of claim 4, wherein said first beam splitter and said fold mirror are adjustably mounted in said first and second cubes, respectively.

6. The system of claim 3, wherein said beam splitter assembly further comprises:

3) a second beam splitter for receiving said reflected image beam, and generating a second, transmitted image beam which is directed to said fold mirror, and a second, twice reflected image beam; and

,

said system further comprises a third tube having a first end attached to said second beam splitter and a second end attached to a third optical imaging device for receiving said second, twice reflected image beam from said second beam splitter.

7. The system of claim 3, wherein said first beam splitter is formed from a dichroic mirror having wavelength selective filtering characteristics.

8. The system of claim 1, wherein said first and second optical imaging devices further comprise first and second CCD cameras.

9. The system of claim 1, wherein said lens assembly further comprises:

1) a reticle positioned at said focal point; and

2) a focusing lens for focusing said real image on said reticle.

10. The system of claim 1, wherein said first and second optical imaging devices are rotatably adjustable relative to said beam splitter assembly to facilitate rotational registration adjustment of the images received by said first and second cameras.

11. A method for generating multiple co-registered optical images comprising the steps of:

a) focusing a real image of an object to be imaged on a focal point;

b) projecting said real image from said focal point through a collimating lens to form a collimated image beam;

c) directing said collimated image beam through a beam splitter, and thereby splitting said collimated image beam into a first, transmitted image beam, and a second, reflected image beam;

d) directing said second, reflected image beam to a fold mirror for generating a third, reflected image beam;

e) directing said first, transmitted image beam through a first lens tube to a first optical imaging device for receiving a first image of said object;

f) directing said third, reflected image beam from said fold mirror through a second lens tube to a second optical imaging device for receiving a second image of said object; and

g) co-registering said first and second images of said object by adjusting the lengths of said first and second lens tubes.

12. The method of claim 11, wherein said step of directing said collimated image beam further comprises directing said collimated image beam through a wavelength selective dichroic mirror beam splitter to form a first, transmitted image beam containing only radiation wavelengths in a first range, and a second, reflected image beam containing only radiation wavelengths in a second range.

13. The method of claim 11, further including the step of rotationally adjusting said first and second optical imaging devices relative to said first and second image beams until said first and second images are co-registered with one another.

14. The method of claim 11, further comprising the step of wavelength filtering said first and third image beams before they are received by said first and second optical imaging devices, respectively.

15. The method of claim 14, wherein said step of filtering is carried out by placing first and second wavelength selective filters in image beam paths of said first and third image beams, respectively.

16. The method of claim 11, wherein said step of focusing a real image comprises directing an image of an object through a focusing lens and onto a reticle positioned at said focal point.