Flat field correction for infrared cameras

• US 8,373,757 B1
• Filed: 02/23/2009
• Issued: 02/12/2013
• Est. Priority Date: 02/23/2009
• Status: Active Grant

• Current Assignee: Teledyne FLIR LLC (Teledyne Technologies Incorporated)
• Original Assignee: FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Inventors: Nguyen, Vu L.
• Primary Examiner(s): Dastouri, Mehrdad
• Assistant Examiner(s): SOSANYA, OBAFEMI OLUDAYO
• Application Number:
  US12/391,156
• Time in Patent Office: 1,450 Days
• Field of Search: 348/164, 348/345, 250/252.1, 250/339.04, 250/347
• US Class Current: 348/164
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

Various techniques are provided to perform flat field correction for infrared cameras. In one example, a method of calibrating an infrared camera includes calibrating a focal plane array (FPA) of the infrared camera to an external scene to determine a set of flat field correction values associated with a first optical path from the external scene to the FPA. The method also includes calibrating the FPA to a shutter of the infrared camera to determine a set of flat field correction values associated with a second optical path from the shutter to the FPA. The method also includes using the flat field correction values associated with the first and second optical paths to calculate a set of supplemental flat field correction values to apply to thermal image data obtained with the infrared camera. The method also includes storing the supplemental flat field correction values.

Claims

1. A method of calibrating an infrared camera, the method comprising:

calibrating a focal plane array (FPA) of the infrared camera to an external scene to determine a first set of flat field correction values associated with a first optical path from the external scene to the FPA;

calibrating the FPA to a shutter of the infrared camera to determine a second set of flat field correction values associated with a second optical path from the shutter to the FPA, wherein the second set of flat field correction values are different than the first set of flat field correction values;

using the first and second set of flat field correction values to calculate a set of supplemental flat field correction values to apply to thermal image data obtained with the infrared camera; and

storing the supplemental flat field correction values to apply to thermal image data of the infrared camera to adjust for non-uniformities associated with the first optical path.

2. The method of claim 1, comprising:

capturing the thermal image data using the FPA; and

applying the supplemental flat field correction values to the thermal image data to adjust for non-uniformities associated with the first optical path.

3. The method of claim 2, wherein the capturing the thermal image data comprises applying the second set of flat field correction values associated with the second optical path to infrared detectors of the FPA to adjust for non-uniformities associated with the second optical path.

4. The method of claim 1, wherein the supplemental flat field correction values are configured to adjust for non-uniformities associated with an optics block of the infrared camera in the first optical path.

5. The method of claim 1, comprising maintaining a plurality of sets of supplemental flat field correction values to adjust for non-uniformities associated with different lenses which may be selectively inserted into the first optical path.

6. The method of claim 1, comprising:

determining a rate of temperature change; and

scaling the supplemental flat field correction values in response to the rate of temperature change before applying the supplemental flat field correction values to the thermal image data.

7. The method of claim 1, comprising inserting the shutter into the first optical path before calibrating the FPA to the shutter.

8. The method of claim 1, wherein the shutter provides a thermal black body internal to the infrared camera, and wherein the shutter is disposed between the FPA and a lens of the infrared camera.

9. The method of claim 1, wherein the external scene comprises a thermal black body external to the infrared camera.

10. A non-transitory machine readable medium on which are stored non-transitory machine readable instructions for performing the method of claim 1.

11. An infrared camera, comprising:

a focal plane array (FPA) adapted to capture thermal image data in response to infrared radiation received by the FPA;

a shutter;

a memory adapted to store a set of supplemental flat field correction values based on a first set of flat field correction values corresponding to a first optical path from an external scene to the FPA and based on a second set of flat field correction values corresponding to a second optical path from the shutter to the FPA; and

a processor adapted to;

calibrate the FPA to the shutter to determine the second set of flat field correction values associated with the second optical path from the shutter to the FPA;

use the first and second set of flat field correction values to calculate the supplemental flat field correction values; and

apply the supplemental flat field correction values to the thermal image data to adjust for non-uniformities associated with the first optical path.

12. The infrared camera of claim 11, wherein the processor is adapted to:

calibrate the FPA to an external scene to determine the first set of flat field correction values associated with the first optical path from the external scene to the FPA;

use the first and second set of flat field correction values associated with the first and second optical paths to calculate a second set of supplemental flat field correction values; and

store the supplemental flat field correction values and the second set of supplemental flat field correction values in the memory.

13. The infrared camera of claim 11, wherein the FPA is adapted to apply the second set of flat field correction values associated with the second optical path to infrared detectors of the FPA to adjust for non-uniformities associated with the second optical path.

14. The infrared camera of claim 11, comprising an optics block in the first optical path, wherein the supplemental flat field correction values are configured to adjust for non-uniformities associated with the optics block.

15. The infrared camera of claim 11, wherein the memory is adapted to store a plurality of sets of supplemental flat field correction values to adjust for non-uniformities associated with different lenses which may be selectively inserted into the first optical path.

16. The infrared camera of claim 11, comprising a temperature sensor, wherein the processor is adapted to:

determine a rate of temperature change in response to the temperature sensor; and

scale the supplemental flat field correction values in response to the rate of temperature change before the supplemental flat field correction values are applied to the thermal image data.

17. The infrared camera of claim 11, wherein the shutter is adapted to be inserted into the first optical path before the FPA is calibrated to the shutter.

18. The infrared camera of claim 11, wherein the shutter provides a thermal black body internal to the infrared camera, and wherein the shutter is located between the FPA and a lens of the infrared camera.

19. The infrared camera of claim 11, wherein the external scene comprises a thermal black body external to the infrared camera.

20. A method of processing thermal image data captured by an infrared camera, the method comprising:

calibrating a focal plane array (FPA) of the infrared camera to determine a first set of flat field correction values associated with an external scene;

calibrating the FPA to determine a second set of flat field correction values associated with a shutter of the infrared camera;

calculating supplemental flat field correction values based on the first and second set of flat field correction values;

storing the supplemental flat field correction values;

capturing thermal image data with the FPA of the infrared camera; and

applying the supplemental flat field correction values to the thermal image data to adjust for non-uniformities associated with the infrared camera, wherein the supplemental flat field correction values are based on differences between the first set of flat field correction values obtained from the calibration of the FPA to the external scene and the second set of flat field correction values obtained from the calibration of the FPA to the shutter of the infrared camera.

21. The method of claim 20, wherein the capturing thermal image data comprises applying the second set of flat field correction values associated with the shutter to infrared detectors of the FPA to adjust for non-uniformities associated with the shutter.

22. The method of claim 20, wherein the supplemental flat field correction values are configured to adjust for non-uniformities associated with an optics block of the infrared camera.

23. The method of claim 20, comprising maintaining a plurality of sets of supplemental flat field correction values to adjust for non-uniformities associated with different lenses which may be selectively provided to the infrared camera.

24. The method of claim 20, comprising:

determining a rate of temperature change; and

scaling the supplemental flat field correction values in response to the rate of temperature change before applying the supplemental flat field correction values to the thermal image data.

25. The method of claim 20, wherein the shutter provides a thermal black body internal to the infrared camera, and wherein the shutter is disposed between the FPA and a lens of the infrared camera.

26. The method of claim 20, wherein the external scene comprises a thermal black body external to the infrared camera.

27. A non-transitory machine readable medium on which are stored non-transitory machine readable instructions for performing the method of claim 20.