Scene-based non-uniformity offset correction for staring arrays

• US 20030198400A1
• Filed: 04/19/2002
• Published: 10/23/2003
• Est. Priority Date: 04/19/2002
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Alderson, Timothy, Tener, Gene
• Granted Patent: US 7,016,550 B2
• Time in Patent Office: Days
• US Class Current: 382/274
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/683 by defect estimation performed on the scene signal, e.g. real time or on the fly detection
• 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

An approach for processing image data is described. The method comprises correcting a frame of image data received from a detector using existing correction coefficients that comprise a plurality of offset coefficients corresponding to a plurality of detector elements. The method also comprises calculating an update parameter for each detector element using pixel data generated from the correction. The update parameter for a given detector element is calculated from multiple difference values determined from a given pixel value of the pixel data and multiple adjacent pixel values. The given pixel value corresponds to the given detector element. Each difference value is determined by subtracting one of the multiple adjacent pixel values from the given pixel value. The method comprises identifying offset coefficients whose existing values are to remain unchanged based upon the update parameters and changing existing values of offset coefficients other than those identified to remain unchanged.

Claims

1. A method of processing image data received from a detector having a plurality of detector elements arranged in a two-dimensional array, the method comprising the steps of:

correcting a frame of image data received from the detector using existing values of a set of correction coefficients, the set of correction coefficients comprising a plurality of offset coefficients corresponding to the plurality of detector elements;

calculating an update parameter for each detector element using pixel data generated from said step of correcting, wherein the update parameter for a given detector element is calculated based upon multiple difference values determined from a given pixel value of the pixel data and multiple adjacent pixel values of the pixel data, the given pixel value corresponding to the given detector element, each difference value being determined by subtracting one of the multiple adjacent pixel values from the given pixel value;

identifying offset coefficients whose existing values are to remain unchanged based upon the update parameters; and

changing existing values of offset coefficients other than those identified to remain unchanged.

2. The method of claim 1, wherein the steps of correcting a frame of image data, calculating an update parameter for each detector element, identifying offset coefficients whose existing values are to remain unchanged, and changing existing values of offset coefficients other than those identified to remain unchanged are repeated iteratively using successive frames of image data from the detector such that updated values of the offset coefficients converge to respective stable values.

3. The method of claim 1, wherein the update parameter (PAR) for a given detector element is calculated according to an expression given by

4. The method of claim 3, wherein the step of identifying comprises:

designating offset coefficients whose existing values are to remain unchanged as those whose corresponding update parameter (PAR) does not satisfy TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are third and fourth threshold values, respectively.

5. The method of claim 4, comprising applying frame integration after the step of correcting, wherein applying frame integration comprises:

multiplying each pixel of corrected image data produced from said correcting by a first fractional number to provide first integration data;

multiplying each pixel of a stored frame of recursively processed image data by a second fractional number to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the step of calculating an update parameter is carried out using the frame-integrated data.

6. The method of claim 5, wherein the step of identifying comprises:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

7. The method of claim 6, wherein the step of changing comprises an action conditionally selected from:

decrementing an existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is positive; and

incrementing the existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is negative.

8. The method of claim 7, wherein said incrementing and decrementing comprise incrementing and decrementing by a predetermined amount.

9. The method of claim 7, wherein N=8 and wherein the multiple adjacent pixel values comprise eight pixels immediately adjacent to the given pixel such that the given pixel and the multiple adjacent pixels form a 3×

3 set of pixels.

10. The method of claim 3, wherein TH1 is approximately equal to a temporal noise level of the detector.

11. The method of claim 10, wherein TH2 is in the range of 2 times the temporal noise level to 2.5 times the temporal noise level.

12. The method of claim 3, wherein TH1 is approximately 1 count.

13. The method of claim 12, wherein TH2 is in the range of 2 to 2.5 counts.

14. The method of claim 1, wherein the step of identifying comprises:

determining whether the update parameter (PAR) for the given detector element satisfies a condition given by TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are two threshold values, respectively; and

when PAR does not satisfy the condition TH3≦

|PAR|≦

TH4, designating the corresponding offset coefficient to remain unchanged.

15. The method of claim 14, wherein the step of identifying comprises:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

16. The method of claim 14, wherein

the update parameter (PAR) for a given detector element is evaluated over a 3×

3 pixel region of the pixel data centered about the given pixel;

the update parameter (PAR) can range between −

8 and +8;

TH3 is selected from the range of 3 to 5; and

TH4 is selected from the range of 6 to 7.

17. The method claim 16, wherein TH3 is 5 and TH4 is 7.

18. The method of claim 1, comprising applying frame integration after the step of correcting, wherein applying frame integration comprises:

multiplying each pixel value of corrected image data produced from said correcting by a first fractional number (f1) to provide first integration data;

multiplying each pixel value of an existing frame of recursively processed image data by a second fractional number (f2) to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the step of calculating an update parameter is carried out using the frame-integrated data.

19. The method of claim 18, wherein f2+f1 =1.

20. The method of claim 19, wherein f2 is selected from the range of 0.90 to 0.99.

21. The method of claim 18, wherein the existing frame of recursively processed image data is generated by successive iterations of processing successive frames of image data from the detector, and wherein the existing frame of recursively processed image data is generated by averaging successive frames of pixel data generated from the step of correcting during the iterations such that each successive stored frame of recursively processed image data is corrected using updated offset coefficients from an immediately preceding iteration.

22. An image processing system for processing image data received from a detector having a plurality of detector elements arranged in a two-dimensional array, comprising:

a memory; and

a processing unit coupled to the memory, wherein the processing unit is programmed to carry out steps of

correcting a frame of image data received from the detector using existing values of a set of correction coefficients, the set of correction coefficients comprising a plurality of offset coefficients corresponding to the plurality of detector elements,

calculating an update parameter for each detector element using pixel data generated from said step of correcting, wherein the update parameter for a given detector element is calculated based upon multiple difference values determined from a given pixel value of the pixel data and multiple adjacent pixel values of the pixel data, the given pixel value corresponding to the given detector element, each difference value being determined by subtracting one of the multiple adjacent pixel values from the given pixel value,

identifying offset coefficients whose existing values are to remain unchanged based upon the update parameters, and

changing existing values of offset coefficients other than those identified to remain unchanged.

23. The image processing system of claim 22, wherein the processing unit iteratively repeats the steps of correcting a frame of image data, calculating an update parameter for each detector element, identifying offset coefficients whose existing values are to remain unchanged, and changing existing values of offset coefficients other than those identified to remain unchanged using successive frames of image data from the detector such that updated values of the offset coefficients converge to respective stable values.

24. The image processing system of claim 22, wherein the update parameter (PAR) for a given detector element is calculated according to an expression given by

25. The image processing system of claim 24, wherein the processing unit carries out the step of identifying by:

designating offset coefficients whose existing values are to remain unchanged as those whose corresponding update parameter (PAR) does not satisfy TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are third and fourth threshold values, respectively.

26. The image processing system of claim 25, wherein the processing unit applies frame integration after the step of correcting by:

multiplying each pixel of corrected image data produced from said correcting by a first fractional number to provide first integration data;

multiplying each pixel of a stored frame of recursively processed image data by a second fractional number to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the processing unit calculates the update parameter using the frame-integrated data.

27. The image processing system of claim 26, wherein the processing unit carries out the step of identifying by:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

28. The image processing system of claim 27, wherein the processing unit carries out the step of changing by executing an action conditionally selected from:

decrementing an existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is positive; and

incrementing the existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is negative.

29. The image processing system of claim 28, wherein said incrementing and decrementing comprise incrementing and decrementing by a predetermined amount.

30. The image processing system of claim 28, wherein N=8 and wherein the multiple adjacent pixel values comprise eight pixels immediately adjacent to the given pixel such that the given pixel and the multiple adjacent pixels form a 3×

3 set of pixels.

31. The image processing system of claim 24, wherein TH1 is approximately equal to a temporal noise level of the detector.

32. The image processing system of claim 31, wherein TH2 is in the range of 2 times the temporal noise level to 2.5 times the temporal noise level.

33. The image processing system of claim 24, wherein TH1 is approximately 1 count.

34. The image processing system of claim 33, wherein TH2 is in the range of 2 to 2.5 counts.

35. The image processing system of claim 22, wherein the processing unit carries out the step of identifying by:

determining whether the update parameter (PAR) for the given detector element satisfies a condition given by TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are two threshold values, respectively; and

when PAR does not satisfy the condition TH3≦

|PAR|≦

TH4, designating the corresponding offset coefficient to remain unchanged.

36. The image processing system of claim 35, wherein the processing unit carries out the step of identifying by:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

37. The image processing system of claim 35, wherein

the update parameter (PAR) for a given detector element is evaluated over a 3×

3 pixel region of the pixel data centered about the given pixel;

the update parameter (PAR) can range between −

8 and +8;

TH3 is selected from the range of 3 to 5; and

TH4 is selected from the range of 6 to 7.

38. The image processing system claim 37, wherein TH3 is 5 and TH4 is 7.

39. The image processing system of claim 22, wherein the processing unit applies frame integration after the step of correcting by:

multiplying each pixel value of corrected image data produced from said correcting by a first fractional number (f1) to provide first integration data;

multiplying each pixel value of an existing frame of recursively processed image data by a second fractional number (f2) to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the processing unit calculates the update parameter using the frame-integrated data.

40. The image processing system of claim 39, wherein f2+f1=1.

41. The image processing system of claim 40, wherein f2 is selected from the range of 0.90 to 0.99.

42. The image processing system of claim 39, wherein the processing unit generates the existing frame of recursively processed image data from successive iterations of processing successive frames of image data from the detector, wherein the existing frame of recursively processed image data is generated by averaging successive frames of pixel data generated from the step of correcting during the iterations such that each successive stored frame of recursively processed image data is corrected using updated offset coefficients from an immediately preceding iteration.

43. A computer-readable carrier containing a computer program adapted to cause a computer to execute steps of:

correcting a frame of image data received from a detector having a plurality of detector elements using existing values of a set of correction coefficients, the set of correction coefficients comprising a plurality of offset coefficients corresponding to the plurality of detector elements;

calculating an update parameter for each detector element using pixel data generated from said step of correcting, wherein the update parameter for a given detector element is calculated based upon multiple difference values determined from a given pixel value of the pixel data and multiple adjacent pixel values of the pixel data, the given pixel value corresponding to the given detector element, each difference value being determined by subtracting one of the multiple adjacent pixel values from the given pixel value;

identifying offset coefficients whose existing values are to remain unchanged based upon the update parameters; and

changing existing values of offset coefficients other than those identified to remain unchanged.

44. The computer-readable carrier of claim 43, wherein the computer-readable carrier is adapted cause the computer to iteratively repeat the steps of correcting a frame of image data, calculating an update parameter for each detector element, identifying offset coefficients whose existing values are to remain unchanged, and changing existing values of offset coefficients other than those identified to remain unchanged using successive frames of image data from the detector such that updated values of the offset coefficients converge to respective stable values.

45. The computer-readable carrier of claim 43, wherein the update parameter (PAR) for a given detector element is calculated according to an expression given by

46. The computer-readable carrier of claim 45, wherein the computer-readable carrier is adapted cause the computer to execute the step of identifying by:

designating offset coefficients whose existing values are to remain unchanged as those whose corresponding update parameter (PAR) does not satisfy TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are third and fourth threshold values, respectively.

47. The computer-readable carrier of claim 46, wherein the computer-readable carrier is adapted cause the computer to apply frame integration after the step of correcting by:

multiplying each pixel of corrected image data produced from said correcting by a first fractional number to provide first integration data;

multiplying each pixel of a stored frame of recursively processed image data by a second fractional number to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the computer-readable carrier is adapted cause the computer to calculate the update parameter using the frame-integrated data.

48. The computer-readable carrier of claim 47, wherein the computer-readable carrier is adapted cause the computer to execute the step of identifying by:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

49. The computer-readable carrier of claim 48, wherein the computer-readable carrier is adapted cause the computer to carry out the step of changing by executing an action conditionally selected from:

decrementing an existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is positive; and

incrementing the existing value of an offset coefficient to be changed when the corresponding update parameter (PAR) is negative.

50. The computer-readable carrier of claim 49, wherein said incrementing and decrementing comprise incrementing and decrementing by a predetermined amount.

51. The computer-readable carrier of claim 49, wherein N=8 and wherein the multiple adjacent pixel values comprise eight pixels immediately adjacent to the given pixel such that the given pixel and the multiple adjacent pixels form a 3×

3 set of pixels.

52. The computer-readable carrier of claim 45, wherein TH1 is approximately equal to a temporal noise level of the detector.

53. The computer-readable carrier of claim 52, wherein TH2 is in the range of 2 times the temporal noise level to 2.5 times the temporal noise level.

54. The computer-readable carrier of claim 45, wherein TH1 is approximately 1 count.

55. The computer-readable carrier of claim 54, wherein TH2 is in the range of 2 to 2.5 counts.

56. The computer-readable carrier of claim 43, wherein the computer-readable carrier is adapted cause the computer to execute the step of identifying by:

determining whether the update parameter (PAR) for the given detector element satisfies a condition given by TH3≦

|PAR|≦

TH4, wherein TH3 and TH4 are two threshold values, respectively; and

when PAR does not satisfy the condition TH3≦

|PAR|≦

TH4, designating the corresponding offset coefficient to remain unchanged.

57. The computer-readable carrier of claim 56, wherein the computer-readable carrier is adapted cause the computer to execute the step of identifying by:

identifying bordering detector elements that border detector elements whose offset coefficients are already designated to remain unchanged; and

designating offset coefficients of the bordering detector elements to remain unchanged.

58. The computer-readable carrier of claim 56, wherein

the update parameter (PAR) for a given detector element is evaluated over a 3×

3 pixel region of the pixel data centered about the given pixel;

the update parameter (PAR) can range between −

8 and +8;

TH3 is selected from the range of 3 to 5; and

TH4 is selected from the range of 6 to 7.

59. The computer-readable carrier claim 58, wherein TH3 is 5 and TH4 is 7.

60. The computer-readable carrier of claim 43, wherein the computer-readable carrier is adapted cause the computer to apply frame integration after the step of correcting by:

multiplying each pixel value of corrected image data produced from said correcting by a first fractional number (f1) to provide first integration data;

multiplying each pixel value of an existing frame of recursively processed image data by a second fractional number (f2) to provide second integration data; and

adding the first integration data and the second integration data to provide frame-integrated data,

wherein the computer-readable carrier is adapted cause the computer to calculate the update parameter using the frame-integrated data.

61. The computer-readable carrier of claim 60, wherein f2+f1=1.

62. The computer-readable carrier of claim 61, wherein f2 is selected from the range of 0.90 to 0.99.

63. The computer-readable carrier of claim 60, wherein the computer-readable carrier is adapted cause the computer to generate the existing frame of recursively processed image data by successive iterations of processing successive frames of image data from the detector, wherein the existing frame of recursively processed image data is generated by averaging successive frames of pixel data generated from the step of correcting during the iterations such that each successive stored frame of recursively processed image data is corrected using updated offset coefficients from an immediately preceding iteration.