Stray light compensation techniques for an infrared camera

Patent metadata

Field	Value
Publication number	US-9979903-B2
Application number	US-201715425913-A
Country	US
Kind code	B2
Filing date	Feb 6, 2017
Priority date	Sep 22, 2011
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

Various techniques are provided for a stray light compensation method for an infrared (IR) camera. For example, a stray light compensation method includes: capturing an IR image of a scene by an IR camera, generating a fixed pattern noise estimate FPNest t0 for time t0 using the captured IR image and a stray light model associated with the IR camera, and performing a fixed pattern noise (FPN) compensation of the captured IR image based on said FPNest t0 to obtain a stray light compensated IR image. The fixed pattern noise estimate may be generated through operations in a frequency domain representation of the captured IR image and the stray light model according to one or more embodiments.

First claim

What is claimed is:

1. A method comprising:
capturing an infrared (IR) image of a scene;
determining a first IR image frequency pattern associated with the captured IR image, wherein the first IR image frequency pattern comprises first frequency components and associated first frequency component amplitudes;
generating a second IR image frequency pattern based at least on the first IR image frequency pattern and a frequency pattern associated with a stray light model, wherein the frequency pattern associated with the stray light model comprises second frequency components and associated second frequency component amplitudes, wherein the second frequency components comprises a set of principal components and a set of non-principal components, and wherein the generating the second IR image frequency pattern comprises adjusting the first frequency component amplitudes of the first IR image frequency pattern corresponding to the set of non-principal components to obtain the second IR image frequency pattern;
generating a fixed pattern noise (FPN) estimate FPNest t0 for time t 0 based at least on the second IR image frequency pattern; and
performing an FPN compensation of the captured IR image based on said FPNest t0 to obtain a stray light compensated IR image.

2. A method comprising:
capturing an infrared (IR) image of a scene;
generating a fixed pattern noise (FPN) estimate FPNest t0 for time t 0 using the captured IR image and a stray light model, wherein the generating the fixed pattern noise estimate-comprises:
performing a transform on said captured IR image to a frequency domain thereby obtaining an IR image frequency pattern, wherein the IR image frequency pattern comprises frequency components with associated frequency component amplitudes and a center frequency, and wherein the stray light model and the transformed IR image have frequency patterns with the same number of and corresponding frequency components;
generating a truncated IR image frequency pattern by setting the frequency component amplitudes of the IR image frequency pattern corresponding to non-principal components of the stray light model to zero;
performing an inverse frequency transform on the truncated IR image frequency pattern to obtain a fixed pattern noise estimate FPNest t0 _ delta for time t 0 ; and
determining the fixed pattern noise estimate FPNest t0 for time t 0 based on said fixed pattern noise estimate FPNest t0 _ delta for time t 0 ; and

performing an FPN compensation of the captured IR image based on said FPNest t0 to obtain a stray light compensated IR image.

3. The method of claim 2 , further comprising:
determining whether the frequency components of the IR image frequency pattern fulfill a first condition based on the stray light model, wherein the first condition is that a correlation measure based on the frequency pattern of the transformed IR image and the stray light model exceeds a predetermined correlation threshold value,
wherein the generating the truncated IR image frequency pattern, the performing the inverse frequency transform, and the determining the fixed pattern noise estimate are performed upon determination that the first condition is fulfilled.

4. The method of claim 1 , further comprising:
generating an adjusted version of the fixed pattern noise estimate FPNest t0 , by adjusting the fixed pattern noise estimate FPNest t0 iteratively until a condition is fulfilled,
wherein the performing the FPN compensation of the captured IR image is based on said adjusted version of the FPNest t0 .

5. The method of claim 2 , wherein determining the fixed pattern noise estimate FPNest t0 for time t 0 is further based on previously determined fixed pattern noise estimate deltas FPNest t-M , . . . , FPNest t-2 , FPNest t-1 .

6. The method of claim 1 , wherein the first IR image frequency pattern and the frequency pattern of the stray light model have the same number of and corresponding frequency components.

7. The method of claim 1 , wherein the determining the first IR image frequency pattern comprises determining a frequency domain representation of the captured IR image to obtain the first IR image frequency pattern.

8. The method of claim 7 , wherein the determining the frequency domain representation comprises performing a transform on the captured IR image to a frequency domain to obtain the frequency domain representation.

9. The method of claim 1 , wherein the adjusting comprises setting the first frequency component amplitudes of the first IR image frequency pattern corresponding to the set of non-principal components associated with the stray light model to zero to obtain the second IR image frequency pattern.

10. The method of claim 1 , wherein each second frequency component of the stray light model is a principal component in the set of principal components or a non-principal component in the set of non-principal components based at least on the corresponding second frequency component amplitude of the second frequency component and one or more threshold values.

11. The method of claim 1 , further comprising:
determining a fixed pattern noise estimate FPNest t0 _ delta for time t 0 based at least on the second IR image frequency pattern, wherein the fixed pattern noise estimate FPNest t0 is based at least on the fixed pattern noise estimate FPNest t0 _ delta for time t 0 .

12. The method of claim 11 , wherein the determining the fixed pattern noise estimate FPNest t0 _ delta for time t 0 is based at least on an inverse frequency transform of the second IR image frequency pattern.

13. The method of claim 11 , wherein the fixed pattern noise estimate FPNest t0 for time t 0 is further based on previously determined fixed pattern noise estimate deltas FPNest t-M , . . . , FPNest t-2 , FPNest t-1 .

14. The method of claim 1 , further comprising:
determining whether the first frequency components of the first IR image frequency pattern fulfill a first condition based on the stray light model, wherein the first condition is that a correlation measure based on the first IR image frequency pattern associated with the captured IR image and the frequency pattern associated with the stray light model exceeds a correlation threshold value, and
wherein the generating the second IR image frequency pattern is performed upon determination that the first condition is fulfilled.

15. A system configured to perform the method of claim 1 , the system comprising:
at least one processor configured to perform the determining the first IR image frequency pattern, the generating the second IR image frequency pattern, the generating the FPN estimate FPNest t0 for time t 0 , and the performing the FPN compensation;
an IR camera configured to perform the capturing the IR image of the scene; and
a memory circuit configured to store the stray light model.

16. The system of claim 15 , wherein the IR camera comprises a housing enclosing the at least one processor and the memory.

17. A system configured to perform the method of claim 2 , the system comprising:
at least one processor configured to perform the generating the FPNest t0 for time t 0 and the performing the FPN compensation;
an IR camera configured to perform the capturing the IR image of the scene; and
a memory circuit configured to store the stray light model.

18. The system of claim 17 , wherein the IR camera comprises a housing enclosing the at least one processor and the memory.

Assignees

• Flir Systems Ab

Inventors

• Johansson Emanuel
• Larson Odd
• Olsson Stefan

Classifications

• G06T7/0002 Primary

  Inspection of images, e.g. flaw detection · CPC title

• H04N23/72

  Combination of two or more compensation controls · CPC title

• G06T2207/20048

  Transform domain processing · CPC title

• H04N25/671 Primary

  for non-uniformity detection or correction · CPC title

• H04N5/33 Primary

  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) · CPC title