Method for fixed pattern noise reduction in infrared imaging cameras

• US 7,880,777 B2
• Filed: 05/25/2006
• Issued: 02/01/2011
• Est. Priority Date: 05/26/2005
• Status: Active Grant

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Anderson, Shane M.
• Primary Examiner(s): Tran; Sinh
• Assistant Examiner(s): Daniels; Anthony J
• Application Number:
  US11/440,754
• Publication Number:
  US 20060279632A1
• Time in Patent Office: 1,713 Days
• Field of Search: 348241-255, 348/164
• US Class Current: 348/241
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/672 between adjacent sensors or output registers for reading a single image
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/674 based on the scene itself, e.g. defocusing
• 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

Methods and systems for correcting fixed pattern noise (FPN) in infrared (IR) imaging cameras. The methods and systems include correcting IR sensor data different strength levels of FPN data and selecting the particular strength level that produces corrected data with the least amount of FPN. The correction may occur over several frames of IR sensor data in order to find an optimal strength level for correction.

Claims

1. A method of correcting fixed pattern noise (FPN) in an infrared (IR) imaging camera, comprising:

receiving at least a portion of a frame of data produced by an array of IR sensors in the camera to produce IR sensor data;

correcting the IR sensor data using multiple strength levels of predetermined FPN data to produce corrected IR sensor data for each strength level, each strength level being a uniform adjustment of the predetermined FPN data;

calculating the relative level of FPN in the corrected IR sensor data for each strength level; and

selecting the strength level that produces reduced levels of FPN remaining in the corrected IR sensor data as the selected strength level to correct IR sensor data.

2. The method of claim 1, further including selecting the corrected IR sensor data at the selected strength level.

3. The method of claim 1, wherein calculating the relative level of FPN includes calculating an objective function for each strength level based on the corrected IR sensor data, each objective function value indicating the relative level of FPN remaining in the corresponding corrected IR sensor data, and selecting the strength level of the predetermined FPN data that produces the lowest objective function level as the selected strength level to correct IR sensor data.

4. The method of claim 3, further including determining spatial averages of the corrected IR sensor for each strength level, the objective function for each strength level being based on the corresponding one of the spatial averages.

5. The method of claim 1, wherein the portion of the frame of data is limited to a portion known to be susceptible to FPN.

6. The method of claim 1, wherein the portion of the frame of data is produced by a row or a column of IR sensors in the array.

7. The method of claim 1, further including performing two-point correction of the IR sensor data.

8. The method of claim 1, further including outputting corrected IR sensor data corrected at the selected strength level towards a display unit or storage unit of the camera.

9. The method of claim 1, wherein the selected strength level of the predetermined FPN data is used to correct the IR sensor data of a subsequent frame of data produced by the array of IR sensors.

10. A method of correcting fixed pattern noise (FPN) in an infrared (IR) imaging camera, comprising:

receiving at least a portion of a frame of data produced by an array of IR sensors in the camera to produce IR sensor data;

correcting the IR sensor data using multiple strength levels of predetermined FPN data to produce corrected IR sensor data for each strength level, each strength level being a uniform adjustment of the predetermined FPN data;

determining spatial averages of the corrected IR sensor data for each strength level;

calculating an objective function value for each strength level based on the corrected IR sensor data and the spatial average data, each objective function value indicating the relative level of FPN remaining in the corrected IR sensor data; and

selecting the strength level of the predetermined FPN data that produces the lowest objective function level as the selected strength level to correct IR sensor data.

11. The method of claim 10, wherein the method is repeated using subsequent frames of data produced by the array of IR sensors, each subsequent frame of data producing IR sensor data, corrected IR sensor data at multiple strength levels, objective function values for each strength level, and a selected strength level that produces the lowest objective function value.

12. The method of claim 11, wherein the multiple strength levels used in each subsequent frame includes the selected strength level from the immediately previous frame.

13. The method of claim 12, wherein the selected strength level produced by subsequent frames of data trends towards an optimal strength level.

14. The method of claim 10, wherein the correction of the IR sensor data includes adding a corresponding one of the multiple strength levels of predetermined FPN data to the IR sensor data for each strength level.

15. The method of claim 10, wherein the spatial average calculation includes subjecting the corrected IR sensor data to a smoothing function.

16. The method of claim 10, wherein the spatial average calculation includes calculating average signal levels produced by groups of adjacent IR sensors in the array.

17. The method of claim 16, wherein the groups of adjacent IR sensors include a portion of a row, a portion of a column, or a block of IR sensors.

18. The method of claim 10, wherein the selected strength level of the predetermined FPN data is used to correct the IR sensor data from the portion of the frame of data.

19. The method of claim 10, wherein the selected strength level of the predetermined FPN data is used to correct the IR sensor data from a second portion of the frame of data produced by the array of IR sensors.

20. The method of claim 10, further including performing two-point correction of the IR sensor data.

21. A method of correcting fixed pattern noise (FPN) in an infrared (IR) imaging camera, comprising:

receiving at least a portion of a first frame of data produced by an array of IR sensors in the camera to produce IR sensor data;

correcting the IR sensor data using at least three strength levels of predetermined FPN data to produce corrected IR sensor data for each strength level, each strength level being a uniform adjustment of the predetermined FPN data;

calculating an objective function value for each strength level based on the corrected IR sensor data, each objective function value indicating the relative level of FPN remaining in the corrected IR sensor data; and

selecting the strength level of the predetermined FPN data that produces the lowest objective function level as the selected strength level to correct IR sensor data; and

using the selected strength level as the intermediate level of the three strength levels for FPN correction of a second frame of data received subsequent to receiving the first frame of data.

22. The method of claim 21, further comprising determining spatial averages of the corrected IR sensor data for each strength level.

23. The method of claim 22, wherein the objective function calculation for each strength level is based on the corresponding spatial average data.

24. The method of claim 23, wherein the objective function calculation includes subtraction of corrected IR sensor data from the spatial average for each strength level to produce difference data.

25. The method of claim 24, wherein the objective function calculation includes calculation of the absolute value of the difference data to produce absolute value data for each strength level.

26. The method of claim 25, wherein the objective function calculation includes clipping the absolute value data at a predetermined maximum value to produce clipped data for each strength level.

27. The method of claim 26, wherein the objective function calculation includes summing the clipped data corresponding to each strength level to total the objective function value for each strength level.

28. A method of correcting fixed pattern noise (FPN) in an infrared (IR) imaging camera, comprising:

receiving at least a portion of sequentially produced frames of data from an array of IR sensors in the camera to produce IR sensor data for each frame;

correcting the IR sensor data within each frame using multiple strength levels of predetermined FPN data to produce corrected IR sensor data for each strength level, each strength level being a uniform adjustment of the predetermined FPN data;

calculating an objective function value for each strength level within each frame based on the corrected IR sensor data, each objective function value indicating the relative level of FPN remaining in the corrected IR sensor data; and

selecting the strength level for each frame that produces the lowest objective function level as the selected strength level to correct IR sensor data, one of the multiple strength levels of each frame being the selected strength level from a previous frame.

29. The method of claim 28, wherein the array of sensors includes a focal plane array of microbolometers.

30. The method of claim 28, wherein the strength levels correspond to different multiples of predetermined FPN coefficients.