Method, apparatus and system providing green-green imbalance compensation

• US 7,830,428 B2
• Filed: 04/12/2007
• Issued: 11/09/2010
• Est. Priority Date: 04/12/2007
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Ovsiannikov, Ilia, Jerdev, Dmitri
• Primary Examiner(s): Ometz; David L
• Assistant Examiner(s): Bemben; Richard
• Application Number:
  US11/783,865
• Publication Number:
  US 20080252759A1
• Time in Patent Office: 1,307 Days
• Field of Search: 382/272, 382162-167, 348/222.1, 348/241, 348/251, 348/207.99, 348266-283, 348294-324, 358518-523
• US Class Current: 348/273
• CPC Class Codes: H04N 2209/045 using mosaic colour filter
• CPC Class Codes: H04N 2209/046 Colour interpolation to calculate the missing colour values
• CPC Class Codes: H04N 23/84 for processing colour signals
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements

Abstract

Method, apparatus and system for determining a value for green-green imbalance and applying the value to green pixels to correct the imbalance are described. Average pixel values of green pixels within a kernel are calculated and an imbalance value is determined based on the averages. The imbalance value is added to or subtracted from all green pixel response values in the kernel to correct the imbalance.

Claims

1. A method of compensating for green-green imbalance in an image captured by a pixel array, comprising:

obtaining a pixel output signal for each green pixel in a kernel of pixels of the image captured by the pixel array;

calculating a green-green imbalance value from each green pixel output signal value associated with the kernel;

adjusting a pixel output value for each green pixel within the kernel by applying the green-green imbalance value; and

outputting the adjusted pixel output value for each green pixel within the kernel.

2. The method of claim 1, wherein applying the green-green imbalance value comprises subtracting the imbalance value from the output values of pixels within a first set of green pixels and adding the imbalance value to output values of pixels within a second set of green pixels.

3. The method of claim 2, wherein the imbalance value is based on a difference between average pixel output values of green pixels within the first set and analogous values for green pixels within the second set.

4. The method of claim 3, wherein the imbalance value is equal to one half of said difference.

5. The method of claim 3, wherein the green pixels within the first set are green pixels in rows alternating green and red pixels.

6. The method of claim 3, wherein the green pixels within the second set are green pixels in rows alternating green and blue pixels.

7. The method of claim 1, wherein the kernel is a 5.times.5 pixel kernel.

8. The method of claim 2, wherein the number of pixels in the first set is equal to the number of pixels in the second set.

9. The method of claim 2, wherein the number of pixels in the first set is not equal to the number of pixels in the second set.

10. The method of claim 1, wherein the imbalance value is selectively applied based on a comparison of average green pixel output values in a first set of pixels within the kernel to average green pixel output values in a second set of pixels within the kernel.

11. The method of claim 1, further comprising:

storing a calculated imbalance value for a kernel of pixels in a temporary imbalance value variable;

calculating a current imbalance value for a next kernel of pixels;

calculating a new imbalance value as equal to;

(α

*temporary imbalance value variable)+(β

*current imbalance value), where α and

β

are predetermined values;

determining a final pixel output value for each green pixel in the next kernel by subtracting the new imbalance value from the output values of pixels within a first set of green pixels within the kernel and adding the new imbalance value to output values of pixels within a second set of green pixels within the kernel; and

storing a new temporary imbalance value variable equal to the new imbalance value.

12. The method of claim 11, wherein .alpha. and .beta. are selected such that α

+β

=1.

13. The method of claim 11, further comprising processing all green pixels outputs in the captured image by repeating the steps for subsequent new kernels at different locations of the image.

14. The method of claim 1 further comprising processing all green pixel output in the captured image by repeating the steps for subsequent new kernels at different locations of the image.

15. The method of claim 11, wherein the temporary imbalance value is stored from kernel to kernel, and is updated in the step of storing a new temporary imbalance value.

16. The method of claim 15, further comprising comparing the new imbalance value to a threshold prior to determining a final pixel output value for each green pixel in the determining step and proceeding to the next kernel if the new imbalance value is greater than the threshold.

17. A method of compensating for green-green imbalance in an image captured by a pixel array, comprising:

obtaining a pixel output signal for each green pixel in a kernel of pixels of the captured image;

calculating a green-green imbalance value from each green pixel output signal value associated with the kernel of pixels of the captured image;

adjusting each green pixel output value within the kernel by applying the green-green imbalance value to the pixel output signal value when the imbalance value is greater than a threshold value; and

outputting the adjusted green pixel output value for each green pixel within the kernel.

18. The method of claim 17, wherein applying the green-green imbalance value comprises subtracting the imbalance value from the output values of pixels within a first set of green pixels and adding the imbalance value to output values of pixels within a second set of green pixels.

19. The method of claim 18, wherein the imbalance value is based on a difference between average pixel output values of green pixels within the first set and green pixels within the second set.

20. The method of claim 19, wherein the imbalance value is equal to one half of said difference.

21. The method of claim 17, wherein the kernel is a 5×

5 pixel kernel.

22. A method of compensating for green-green imbalance in a image captured by a pixel array, comprising:

determining a first average pixel output value of a first set of green pixels in a kernel of pixels of an image captured by the array;

determining a second average pixel output value of a second set of green pixels in the kernel;

comparing the first average pixel output value with the second average pixel output value to determine a higher average pixel output value and a lower average pixel output value;

determining an imbalance value based on the difference between the higher average pixel output value and the lower average pixel output value;

setting the imbalance value equal to zero when the imbalance value is greater than a threshold value;

determining a final output value of pixels in the set of green pixels having the lower average output value by adding the imbalance value to the corresponding pixel output value; and

determining a final output value of pixels in the set of green pixels having the higher average output value by subtracting the imbalance value from the corresponding pixel output value.

23. The method of claim 22, wherein the imbalance value is equal to one half of the difference between the higher average pixel output value and the lower average pixel output value.

24. The method of claim 23, wherein the green pixels in the first set are in rows of pixels having alternating green and red pixels.

25. The method of claim 23, wherein the green pixels in the first set are in rows of pixels having alternating green and blue pixels.

26. The method of claim 23, wherein the number of pixels in the first set is equal to the number of pixels in the second set.

27. The method of claim 23, wherein the number of pixels in the first set is not equal to the number of pixels in the second set.

28. The method of claim 23, wherein the first and second sets of green pixels are selected from within an A×

B pixel kernel, wherein A=5 and B=5.

29. A method of compensating for green-green imbalance in an image captured by a pixel array, comprising:

obtaining a pixel output signal for a plurality of green pixels within a kernel of pixels in the captured image;

storing a calculated imbalance value for the kernel of pixels of the image in a temporary imbalance value variable;

calculating a current imbalance value for a next kernel of pixels;

calculating a new imbalance value as equal to;

(α

*temporary imbalance value variable)+(β

*current imbalance value), where α and

β

are predetermined values;

determining a final pixel output value for each green pixel in the next kernel by subtracting the new imbalance value from the output values of pixels within a first set of green pixels within the kernel and adding the new imbalance value to output values of pixels within a second set of green pixels within the kernel;

storing a new temporary imbalance value variable equal to the new imbalance value; and

outputting the final pixel output value for each green pixel in the next kernel.

30. The method of claim 29, wherein α

and β

are selected such that α

+β

=1.

31. The method of claim 29, further comprising processing all pixels outputs in the captured image by repeating the steps for subsequent new kernels.

32. The method of claim 29, wherein the temporary imbalance value is stored from kernel to kernel, and is updated in the step of storing a new temporary imbalance value.

33. The method of claim 32, further comprising comparing the new imbalance value to a threshold prior to determining a final pixel output value for each green pixel in the determining step and proceeding to a subsequent kernel without correcting imbalance in the current kernel if the new imbalance value is greater than the threshold.

34. The method of claim 31, wherein the current imbalance value is calculated as equal to one half of the difference in average pixel output values between two exclusive sets of green pixels within the respective kernels.

35. An imaging device, comprising:

a color pixel array;

a processor for processing captured image pixel output signals received from the pixel array, the processor being configured to;

calculate a green-green imbalance value based on a difference in average pixel output signal values between two exclusive sets of green pixels associated with a kernel of the captured image, where a first set has a higher average pixel output value and a second set has a lower average pixel output value; and

adjust the pixel output value for each green pixel in the kernel by applying the imbalance value.

36. The imaging device of claim 35, wherein applying the imbalance value comprises subtracting the imbalance value from the output values of pixels within the first set and adding the imbalance value to output values of pixels within the second set.

37. The imaging device of claim 35, wherein the imbalance value is equal to one half of the difference between the average pixel value of pixels within the first set and the average pixel value of pixels within the second set.

38. The imaging device of claim 35, wherein the green pixels in the first set are from rows of pixels having alternating green and red pixels.

39. The imaging device of claim 35, wherein the green pixels in the second set are from rows of pixels having alternating green and blue pixels.

40. An imaging device, comprising:

a pixel array;

a processor for processing captured image pixel output signals received from the pixel array, the processor being configured to;

store a calculated imbalance value for a kernel of pixels in a temporary imbalance value variable;

calculate a current imbalance value for a next kernel of pixels;

calculate a new imbalance value as equal to;

(α

*temporary imbalance value variable)+(β

*current imbalance value), where α and

β

are predetermined values;

determine a final pixel output value for each green pixel in the next kernel by subtracting the new imbalance value from the output values of pixels within a first set of green pixels within the kernel and adding the new imbalance value to output values of pixels within a second set of green pixels within the kernel; and

store a new temporary imbalance value variable equal to the new imbalance value.

41. The imaging device of claim 40, wherein α

and β

are selected such that α

+β

=1.

42. The imaging device of claim 40, further comprising processing all pixels outputs in the captured image by repeating the steps for subsequent new kernels.

43. The imaging device of claim 40, wherein the temporary imbalance value is stored from kernel to kernel, and is updated in the step of storing a new temporary imbalance value.

44. The imaging device of claim 43, further comprising comparing the new imbalance value to a threshold prior to determining a final pixel output value for each green pixel in the determining step and proceeding to a subsequent kernel without subtracting or adding the imbalance value to the pixel output values of the current kernel if the new imbalance value is greater than the threshold.

45. The imaging device of claim 42, wherein the current imbalance value is calculated as equal to one half of the difference in average pixel output values between two exclusive sets of green pixels within the respective kernels.

46. A digital camera system, comprising:

a pixel array for capturing an image received through a lens;

a processor circuit for processing pixel signals received from the pixel array, the processor circuit being configured to;

calculate an imbalance value based on a difference in average pixel output values between two exclusive sets of green pixels associated with a kernel, where a first set has a higher average pixel output value and a second set has a lower average pixel output value; and

adjust pixel output for each green pixel in the kernel by applying the imbalance value to each pixel output value.

47. The digital camera system of claim 46, wherein the application of the imbalance value comprises subtracting the imbalance value from the output values of pixels within the first set and adding the imbalance value to output values of pixels within the second set.

48. The digital camera system of claim 46, wherein the imbalance value is equal to one half of the difference between the average pixel value of pixels within the first set and the average pixel value of pixels within the second set.

49. The digital camera system of claim 46, wherein the green pixels selected in the first set are in rows of alternating green and red pixels.

50. The digital camera system of claim 46, wherein the green pixels in the second set are in rows of alternating green and blue pixels.

51. A storage medium containing a program for a processor, said program when executed by said processor performing the acts of:

determining a first average pixel output value representing a first set of green pixels in a kernel of a captured image;

determining a second average output value representing a second set of green pixels in the kernel;

comparing the first average output value with the second average output value to determine a higher average output value and a lower average output value;

determining an imbalance value based on the difference between the higher average output value and the lower average output value;

setting the imbalance value equal to zero when the imbalance value is greater than a threshold value;

determining final output values representing pixels in the set of green pixels having the lower average output value by adding the imbalance value to the corresponding output values; and

determining final output values representing pixels in the set of green pixels having the higher average output value by subtracting the imbalance value from the corresponding output values.

52. The storage medium of claim 51, wherein the imbalance value is equal to one half of the difference between the higher average output value and the lower average output value.

53. A storage medium containing a program for execution by a processor, said program when executed by the processor causing the processor to perform the acts of:

storing a calculated imbalance value for a kernel of pixels in a temporary imbalance value variable;

calculating a current imbalance value for a next kernel of pixels;

calculating a new imbalance value as equal to;

(α

*temporary imbalance value variable)+(β

*current imbalance value), where α and

β

are predetermined values;

determining a final pixel output value for each green pixel in the next kernel by subtracting the new imbalance value from the output values of pixels within a first set of green pixels within the kernel and adding the new imbalance value to output values of pixels within a second set of green pixels within the kernel; and

storing a new temporary imbalance value variable equal to the new imbalance value.

54. The storage medium of claim 53, wherein α

and β

are selected such that a +β

=1.

55. The storage medium of claim 53, further comprising processing all pixels outputs in the captured image by repeating the steps for subsequent new kernels.

56. The storage medium of claim 55, wherein the temporary imbalance value is stored from kernel, and is updated in the determining step.