Hyperspectral Resolution Using Three-Color Camera

• US 20160132748A1
• Filed: 11/07/2014
• Published: 05/12/2016
• Est. Priority Date: 11/07/2014
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Tillotson, Brian J.
• Granted Patent: US 9,576,216 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B64U 2101/31 for surveillance
• CPC Class Codes: G01J 2003/1213 Filters in general, e.g. dichroic, band
• CPC Class Codes: G01J 2003/1226 Interference filters
• CPC Class Codes: G01J 3/00 Spectrometry; Spectrophotometry; Monochromators; Measuring colours
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G02B 5/201 in the form of arrays
• CPC Class Codes: G02B 5/28 Interference filters
• CPC Class Codes: G06V 20/194 using hyperspectral data, i.e. more or other wavelengths than RGB
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/12 with one sensor only
• CPC Class Codes: H04N 23/80 Camera processing pipelines; Components thereof

Abstract

A method for capturing hyperspectral images using a regular color camera. In the method, the camera takes multiple images of a scene, with the camera oriented differently for each image. For a camera carried by an aircraft or spacecraft, this allows hyperspectral imaging without the cost or weight of a hyperspectral camera.

Claims

1. A method for measuring the spectrum of at least one point in a scene, comprising:

characterizing a camera which comprises a multi-color filter array and an array of photosensors;

locating the camera at a position with a first orientation so that a scene is within a field of view of the camera;

capturing a first image of the scene while the camera is at said position with said first orientation;

locating the camera at said position with a second orientation so that the scene is within the field of view of the camera;

capturing a second image of the scene while the camera is at said position with said second orientation;

transferring the first and second images from the camera to a computer; and

computing the spectrum of a point in the scene based on at least said first and second images, said computing being performed by the computer system.

2. The method as recited in claim 1, wherein characterizing the camera comprises measuring a transmittance as a function of wavelength and of incidence angle.

3. The method as recited in claim 1, wherein the point in the scene is imaged in the first image at a first distance from the optical axis of the camera, and the point in the scene is imaged in the second image at a second distance from the optical axis of the camera, the second distance being different than the first distance.

4. The method as recited in claim 1, wherein the first image comprises a first pixel corresponding to the point in the scene, and the second image comprises a second pixel corresponding to the point in the scene, the first and second pixels respectively comprising first and second RGB triplets of intensity values.

5. The method as recited in claim 4, further comprising:

computing a first set of transmittance values for a multiplicity of synthetic spectral bands at a first angle of incidence of a light ray from the point in the scene to a first photosensor corresponding to the first pixel;

computing a second set of transmittance values for the multiplicity of synthetic spectral bands at a second angle of incidence of a light ray from the point in the scene to a second photosensor corresponding to the second pixel; and

forming a matrix of transmittance values that includes the first and second sets of transmittance values,

wherein computing the spectrum comprises respectively multiplying the intensity values of the first and second RGB triplets by elements of a matrix which is an inverse of the matrix of transmittance values.

6. The method as recited in claim 1, wherein the camera is attached to a vehicle or a robot.

7. The method as recited in claim 6 wherein locating the camera comprises maneuvering the vehicle or robot.

8. The method as recited in claim 6, wherein the vehicle is one of the following group:

an aircraft, a spacecraft, a ground vehicle, a boat, or a submersible.

9. The method as recited in claim 1, wherein the computed spectrum comprises intensity values for each of a multiplicity of synthetic spectral bands.

10. The method as recited in claim 9, wherein at least one synthetic spectral band is chosen after capture of the first image.

11. A method for measuring the spectrum of at least one point in a scene, comprising:

characterizing a camera which comprises a multi-color filter array and an array of photosensors;

mounting the camera on an unmanned aerial vehicle;

flying the unmanned aerial, vehicle along a first flight path, the unmanned aerial vehicle being oriented such that the camera has a first orientation, a scene is within a field of view of the camera, and light from a point in the scene impinges on a first photosensor of the camera;

capturing a first image of the scene while light from the point in the scene is impinging on the first photosensor;

flying the unmanned aerial vehicle along a second flight path, the unmanned aerial vehicle being oriented such that the camera has a second orientation different than the first orientation, the scene is within the field of view of the camera, and light from the point in the scene impinges on a second photosensor of the camera;

capturing a second image of the scene while light from the point in the scene is impinging on the second photosensor;

transferring the first and second images from the camera to a computer; and

computing the spectrum of the point in the scene based on at least the first and second images, said computing being performed by the computer system.

12. The method as recited in claim 11, wherein characterizing the camera comprises measuring a transmittance as a function of wavelength and of incidence angle.

13. The method as recited in claim 11, wherein the first image comprises a first pixel corresponding to the point in the scene, and the second image comprises a second pixel corresponding to the point in the scene, the first and second pixels respectively comprising first and second RGB triplets of intensity values.

14. The method as recited in claim 13, further comprising:

computing a first set of transmittance values for a multiplicity of synthetic spectral bands at a first angle of incidence of a light ray from the point in the scene to the first photosensor;

computing a second set of transmittance values for the multiplicity of synthetic spectral bands at a second angle of incidence of a light ray from the point in the scene to the second photosensor; and

forming a matrix of transmittance values that includes the first and second sets of transmittance values,

wherein computing the spectrum comprises respectively multiplying the intensity values of the first and second RGB triplets by elements of a matrix which is an inverse of the matrix of transmittance values.

15. The method as recited in claim 11, wherein the computed spectrum comprises intensity values for each of a multiplicity of synthetic spectral bands.

16. A system for measuring the spectrum of at least one point in a scene, comprising:

a color camera comprising a multi-color filter array and an array of photosensors covered by said multi-color filter array; and

a computer system for receiving images from said color camera, said computer system comprising memory for storing a characterization of said color camera and being programmed to perform the following operations;

computing the spectrum of a point in the scene based on multi-color intensity values of light from the point in the scene which impinges on respective photosensors during capture of respective images of the scene by said color camera.

17. The system as recited in claim 16, wherein said characterization of the camera comprises transmittance values which are a function of wavelength and of incidence angle.

18. The system as recited in claim 16, wherein said computer system is further programmed to perform the following operations:

computing a first set of transmittance values for a multiplicity of synthetic spectral bands at a first angle of incidence of a light ray from the point in the scene to a first photosensor;

computing a second set of transmittance values for the multiplicity of synthetic spectral bands at a second angle of incidence of a light ray from the point in the scene to a second photosensor; and

forming a matrix of transmittance values that includes the first and second sets of transmittance values,

wherein computing the spectrum comprises multiplying the multi-color intensity values by elements of a matrix which is an inverse of the matrix of transmittance values.

19. The system as recited in claim 16, further comprising a vehicle or a robot, said color camera being attached to said vehicle or said robot.

20. The system as recited in claim 16, wherein the computed spectrum comprises intensity values for each of a multiplicity of synthetic spectral bands.