Non-uniformity error correction with a bilateral filter

• US 8,428,385 B2
• Filed: 06/24/2009
• Issued: 04/23/2013
• Est. Priority Date: 06/24/2009
• Status: Active Grant

• Current Assignee: Teledyne FLIR LLC (Teledyne Technologies Incorporated)
• Original Assignee: FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Inventors: Whiteside, Randel S., Archer, Cynthia I.
• Primary Examiner(s): STREGE, JOHN B
• Application Number:
  US12/491,165
• Publication Number:
  US 20100329583A1
• Time in Patent Office: 1,399 Days
• Field of Search: 382/254, 382/255, 382/274, 382/275, 382/260, 356/446
• US Class Current: 382/260
• CPC Class Codes: G06T 2207/10004 Still image; Photographic image
• CPC Class Codes: G06T 2207/20028 Bilateral filtering
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• 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

Correction of spatial nonuniformities among detectors in a focal plane array. Incoming image data is incident on the array, and the resulting image signals are corrected with a bilateral filter. The bilateral filter accounts for edge effects by filtering based both on spatial separation between image points and photometric separation between image points.

Claims

1. A non-uniformity error correction system, comprising:

a plurality of detectors disposed substantially within a planar array, the detectors configured to receive changing image data and to produce sequential image signals in response, each image signal corresponding to one respective pixel in an overall image; and

a processor configured to receive the image signals produced by the detectors and to apply a bilateral filter to the signals, the bilateral filter being a function of both a spatial separation and a photometric separation between each pixel and each one of an associated neighborhood of pixels;

wherein the bilateral filter is configured to at least partially correct the image signals for non-uniformity errors among the detectors; and

wherein the associated neighborhood of pixels excludes pixels having a photometric separation greater than a threshold value.

2. The system of claim 1, wherein the photometric separation between pixels is a function of a difference in intensity between the pixels.

3. The system of claim 1, wherein the photometric separation between pixels is a function of a difference in color between the pixels.

4. The system of claim 1, wherein the bilateral filter is defined using the product of a first weight factor that depends on spatial separation between pixels and a second weight factor that depends on photometric separation between the pixels.

5. The system of claim 4, wherein the first weight factor is a Gaussian function of spatial separation characterized by a first width parameter, and the second weight factor is a Gaussian function of photometric separation characterized by a second width parameter.

6. The system of claim 5, wherein the second weight factor is a Gaussian function of intensity difference.

7. The system of claim 1, further comprising a dithering mechanism configured to spatially translate incoming image data such that detector non-uniformity error frequency is lower than scene information frequency and temporal noise frequency;

wherein the processor is further configured to remove the lower frequency detector non-uniformity errors from the signals and to iteratively update detector offset correction data based on non-uniformity errors removed by processor.

8. The system of claim 7, wherein the incoming image data substantially changes more than once per second, and the dithering mechanism is further configured to spatially translate the incoming image data with a frequency of less than one cycle per second.

9. The system of claim 1, wherein the processor is further configured to detect scene motion and to iteratively update detector offset correction data based on non-uniformity errors removed by the bilateral filter when sufficient scene motion is detected.

19. The system of claim 1, wherein the processor is configured to automatically adapt the threshold value in response to a change in image conditions over time.

20. The system of claim 19, wherein the processor is configured to adapt the threshold value in response to a change in a non-uniformity correction metric, the non-uniformity correction metric corresponding to an amount of non-uniformity error correction by the system.

21. The system of claim 19, wherein adapting the threshold includes lowering the threshold value in response to an increase in an amount of non-uniformity error correction.

22. The system of claim 1, wherein the threshold value is a first threshold value, and the associated neighborhood of pixels further excludes pixels having a spatial separation greater than a second threshold value.

23. The system of claim 22, wherein the processor is configured to automatically adapt the second threshold value by raising the second threshold value in response to an increase in an amount of non-uniformity error correction.

10. A method of correcting focal plane array non-uniformity errors, comprising:

receiving changing image data at a substantially planar array of detectors;

producing image signals with the array of detectors in response to the received image data, each image signal corresponding to one respective pixel in an overall image;

applying a bilateral filter to the image signals produced by the detectors to at least partially correct the signals for non-uniformity errors among the detectors, the bilateral filter being a function of both a spatial separation and a photometric separation between each pixel and each one of an associated neighborhood of pixels; and

excluding from the associated neighborhood of pixels those pixels having a photometric separation greater than a threshold value.

11. The method of claim 10, wherein the bilateral filter is defined using the product of a first weight factor that depends on spatial separation between pixels and a second weight factor that depends on photometric separation between the pixels.

12. The method of claim 11, wherein the first weight factor is a Gaussian function of spatial separation characterized by a first width parameter, and the second weight factor is a Gaussian function of photometric separation characterized by a second width parameter.

13. The method of claim 12, wherein the second weight factor is a Gaussian function of intensity difference.

14. The method of claim 10, further comprising iteratively updating detector offset correction data based on non-uniformity errors corrected by the bilateral filter.

15. The method of claim 14, further comprising spatially translating the data prior to receiving the image data at the array of detectors.

16. The method of claim 15, wherein spatially translating the data occurs at a first frequency less than one cycle per second, and the image data changes at a second frequency greater than one cycle per second.

17. The method of claim 14, further comprising detecting scene motion by comparing a captured image frame with a reference frame, and iteratively updating the detector offset correction data only if scene motion exceeds a predetermined amount.

24. The method of claim 10, further including adapting the threshold value in response to a change in image conditions over time.

25. The method of claim 24, wherein adapting the threshold value includes lowering the threshold value in response to an increase in an amount of non-uniformity error correction.

26. The method of claim 10, wherein the threshold value is a first threshold value, and the method further includes:

excluding from the associated neighborhood of pixels those pixels having a spatial separation greater than a second threshold value; and

automatically adapting the second threshold value by raising the second threshold value in response to an increase in an amount of non-uniformity error correction.

18. A non-uniformity error correction system, comprising:

a dithering mechanism configured to spatially translate image data on a focal plane array of infrared radiation detectors; and

a processor configured to receive image signals produced by the array of detectors, to at least partially correct the image signals for non-uniformity errors among the detectors by applying a bilateral filter to the signals, and to remove translation effects of the dithering mechanism from the signals;

wherein the bilateral filter is defined using the mathematical product of a function of spatial separation between the image signals and a function of photometric separation between the image signals, and wherein the bilateral filter does not consider image signals having a photometric separation greater than a threshold value.