Method and apparatus for color non-uniformity correction in a digital camera

1. A method of correcting color-dependent vignetting in a digital camera, the method comprising:

providing, for each color that said camera can image, a raw array of data corresponding to an image of a desired scene;

providing a plurality of candidate first sets of polynomial coefficients,

each first set representing calibration polynomials that describe second sets of color-specific arrays of calibration coefficients, respectively, the calibration coefficients being appropriate to at least one combination of parameter values to which the camera could have been set when the respective raw arrays were captured;

determining values of operating parameters to which parameters of the camera were adjusted when the respective raw arrays were captured;

selecting a first set from among the plurality of candidates based upon the determined values; and

changing the raw arrays according to the selected first set such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays.

2. The method of claim 1 , wherein said changing produces changed arrays, the method further comprising:

storing each changed array as the respective data array corresponding to said desired image.

3. The method of claim 2 , wherein said storing overwrites locations of said raw arrays in memory with corresponding values of the changed arrays, respectively.

4. The method of claim 1 , wherein said changing is performed entirely by processing circuitry within said camera or entirely by a processor external to said camera.

5. The method of claim 1 , wherein said providing provides a red array, a green array and a blue array for each desired scene.

6. The method of claim 1 , wherein said providing includes: capturing, via said camera, said raw array of data for each color.

7. The method of claim 1 , wherein:

the first sets correspond to a plurality of combinations of values for camera operating parameters, respectively.

8. The method of claim 7 , wherein:

for the raw array corresponding to each color, said changing includes processing each raw array of color data using the corresponding calibration polynomial so as, for each pixel, to do at least the following,

determine a calibration coefficient for the pixel based upon the corresponding calibration polynomial equation, and

scale the pixel by the corresponding calibration coefficient.

9. The method of claim 8 , wherein:

a total number of possible combinations of parameter values to which said camera parameters could be set is greater than the number of said first sets; and

the step of selecting a first set includes at least the following,

selecting from among the first sets based upon a predetermined mapping between the total number of parameter-value combinations and said first sets.

10. The method of claim 9 ,

wherein said mapping maps from said total number of parameter-value combinations to said first sets are based upon zoom setting and aperture, said mapping treating other ones of said parameters as don't-care conditions.

11. The method of claim 10 ,

wherein said zoom setting can include the values wide, medium and telephoto, and said aperture can include the values A and B; and

wherein said first sets include sets corresponding to the following pairings of zoom setting and aperture: wide zoom and aperture A; medium zoom and aperture A; telephoto zoom and aperture A; wide zoom and aperture B; medium zoom and aperture B; and telephoto zoom and aperture B.

12. The method of claim 10 , wherein said mapping is look-up table mapping.

13. A system of correcting color-dependent vignetting in a digital camera, the system comprising:

an imager to provide for each color that said camera can image, a raw array of data corresponding to an image of a desired scene;

a memory to store a plurality of candidate first sets of polynomial coefficients,

each first set representing calibration polynomials that describe second sets of color-specific arrays of calibration coefficients, respectively, the calibration coefficients being appropriate to at least one combination of parameter values to which the camera could have been set when the respective raw arrays were captured; and

processing circuitry to do at least the following,

determine values of operating parameters to which parameters of the camera were adjusted when the respective raw arrays were captured,

select a first set from among the plurality of candidates based upon the determined values, and

change the raw arrays according to the selected first set such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays.

14. The system of claim 13 , wherein said processing circuitry also is operable at least to produce changed arrays, the system further comprising:

at least one memory to store the changed arrays as the respective data arrays corresponding to said desired image.

15. The system of claim 13 , wherein said processing circuitry also is operable at least to overwrite locations of said raw arrays in memory with corresponding values of the changed arrays, respectively.

16. The system of claim 13 , wherein said processing circuitry is one of processing circuitry within said camera or processing circuitry external to said camera.

17. The system of claim 13 , wherein said imager is operable to image a red array, a green array and a blue array for each desired scene.

18. The system of claim 13 , wherein said imager is operable to capture, via said camera, said raw array of data for each color.

19. The system of claim 13 , wherein:

the first sets correspond to a plurality of combinations of values for camera operating parameters, respectively.

20. The system of claim 19 , wherein:

for the raw array corresponding to each color, said processing circuitry is operable to process each raw array of color data using the corresponding calibration polynomial so as, for each pixel, to do at least the following:

determine a calibration coefficient for the pixel based upon the corresponding calibration polynomial equation; and

scale the pixel by the corresponding calibration coefficient.

21. The system of claim 20 , wherein:

a total number of possible combinations of parameter values to which said camera parameters could be set is greater than the number of said first plurality of coefficient sets; and

said processing circuitry also is operable at least to select from among the first sets based upon a predetermined mapping between the total number of parameter-value combinations and said first sets.

22. The system of claim 21 , further comprising a look-up table wherein said mapping is stored.

23. The system of claim 21 ,

wherein said mapping is from said total number of parameter-value combinations to said first sets based upon zoom setting and aperture.

24. The system of claim 23 ,

wherein said zoom setting can include the values wide, medium and telephoto, and said aperture can include the values A and B; and

wherein said first sets includes sets corresponding to the following pairings of zoom setting and aperture: wide zoom and aperture A; medium zoom and aperture A; telephoto zoom and aperture A; wide zoom and aperture B; medium zoom and aperture B; and telephoto zoom and aperture B.

25. A system of correcting color-dependent vignetting in a digital camera, the system comprising:

imaging means for providing, for each color that said camera can image, a raw array of data corresponding to an image of a desired scene;

a memory to store a plurality of candidate first sets of polynomial coefficients,

each first set representing calibration polynomials that describe second sets of color-specific arrays of calibration coefficients, respectively, the calibration coefficients being appropriate to at least one combination of parameter values to which the camera could have been set when the respective raw arrays were captured;

means for determining values of operating parameters to which parameters of the camera were adjusted when the respective raw arrays were captured;

means for selecting a first set from among the plurality of candidates based upon the determined values; and

means for changing the raw arrays according to the selected first set such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays.

26. The system of claim 25 , wherein:

the first sets correspond to a plurality of combinations of values for camera operating parameters, respectively.

27. A computer-readable medium having code portions embodied thereon that, when read by a processor, cause said processor to perform the method of claim 1 .

28. A method of correcting color-dependent vignetting in a digital camera, the method comprising:

providing, for each color that said camera can image, a raw array of data corresponding to an image of a desired scene; and

changing the raw arrays such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays;

wherein the step of changing includes reducing an amount of color-dependent vignetting without necessarily having to reduce an amount of non-color-dependent vignetting.

29. A system of correcting color-dependent vignetting in a digital camera, the system comprising:

an imager to provide for each color that said camera can image, a raw array of data corresponding to an image of a desired scene; and

processing circuitry to change the raw arrays such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays;

wherein the processing circuitry is operable to change the raw arrays by being further operable to reduce an amount of color-dependent vignetting without necessarily having to reduce an amount of non-color-dependent vignetting.

30. A system of correcting color-dependent vignetting in a digital camera, the system comprising:

imaging means for providing, for each color that said camera can image, a raw array of data corresponding to an image of a desired scene; and

camera means for changing the raw arrays such that the array for each color exhibits substantially the same amount of vignetting so as to reduce color-dependent vignetting in a composite image based upon each of the changed arrays;

wherein the camera means for changing the raw arrays is further for reducing an amount of color-dependent vignetting without necessarily having to reduce an amount of non-color-dependent vignetting.