Dynamic color shading correction

1. A method in an electronic device for correcting color shading artifacts in a captured image, the method comprising: receiving image data comprising the captured image and scene statistics, the scene statistics comprising a downsampled version of the captured image; accessing a reference table, wherein the reference table comprises shading correction data calibrated under a typical illumination; correcting color shading in the scene statistics using the reference table; estimating color shading in the corrected scene statistics; updating the reference table based on the estimated color shading; and correcting color shading in the captured image using the updated reference table.

2. The method of claim 1 , wherein estimating color shading comprises separating a first color shading component from an intrinsic color component, wherein the intrinsic color component represents the true hue content of the captured image.

3. The method of claim 2 , wherein estimating color shading further comprises transforming the scene statistics into at least one hue channel and estimating the first color shading component from the at least one hue channel.

4. The method of claim 2 , further comprising separating a second color shading component from the intrinsic color component.

5. The method of claim 4 , wherein the first color shading component is estimated from a R/G hue channel and wherein the second color shading component is estimated from a B/G hue channel.

6. The method of claim 1 , wherein estimating color shading is performed using an iterative color shading estimation process.

7. The method of claim 6 , wherein the iterative color shading estimation process alternately solves for a value of a color shading component using a fixed intrinsic color component value, wherein the intrinsic color component represents the true hue content of the captured image, and for a value of the intrinsic color component using a fixed color shading component value until the value of the color shading component and the value of the intrinsic color component converge.

8. The method of claim 7 , wherein alternately solving for the value of the color shading component and the value of the intrinsic color component comprises using an augmented Lagrangian function.

9. The method of claim 7 , further comprising solving for a plurality of partial gradients.

10. The method of claim 1 , wherein estimating color shading is performed using an aggressive color shading estimation process.

11. The method of claim 10 , wherein the aggressive color shading estimation process comprises detecting a plurality of partial gradients of a color shading component directly from at least one hue component of the scene statistics.

12. The method of claim 11 , wherein the aggressive color shading estimation process further comprises reconstructing the color shading component from the plurality of partial gradients.

13. The method of claim 1 , wherein the image data comprises a video sequence comprising a plurality of image frames.

14. The method of claim 13 , further comprising: estimating color shading in each of the plurality of image frames; generating an updated reference table for each of the plurality of image frames; and correcting color shading in each of the plurality of image frames.

15. The method of claim 14 , wherein the color shading artifacts in the plurality of image frames in the video sequence are corrected in real time.

16. The method of claim 1 , wherein the reference table comprises a plurality of sub-tables, wherein each of the plurality of sub-tables is associated with one of a plurality of Bayer channels.

17. A dynamic color shading correction apparatus, comprising: a correction table data repository configured to store a reference table, wherein the reference table comprises shading correction data calibrated on a reference module under a typical illumination; and a processor configured to receive image data comprising a captured image and scene statistics, the scene statistics comprising a downsampled version of the captured image, and to perform preliminary color shading correction on the scene statistics using the reference table; estimate color shading in the scene statistics; generate an updated table from the reference table and the estimated color shading; and correct color shading artifacts in the image data using the updated table.

18. The dynamic color shading correction apparatus of claim 17 , wherein the correction table data repository is further configured to store a plurality of sub-tables of the reference table, wherein each of the plurality of sub-tables is associated with one of a plurality of Bayer channels.

19. The dynamic color shading correction apparatus of claim 18 , wherein the processor is further configured to estimate color shading in at least one of the plurality of Bayer channels in the scene statistics.

20. The dynamic color shading correction apparatus of claim 19 , wherein processor is configured to update the plurality of sub-tables using a corresponding estimated color shading in the at least one of the plurality of Bayer channels.

21. The dynamic color shading correction apparatus of claim 17 , wherein the processor is further configured to perform an iterative color shading estimation process.

22. The dynamic color shading correction apparatus of claim 17 , wherein the color shading estimation module is configured to perform an aggressive color shading estimation process.

23. The dynamic color shading correction apparatus of claim 17 , further comprising an image sensor associated with a filter.

24. The dynamic color shading correction apparatus of claim 23 , wherein the filter is a reflective infrared cut-off filter.

25. The dynamic color shading correction apparatus of claim 24 , wherein the image sensor comprises a center region and a plurality of edge regions, and different spectra of incident light passing through the infrared cut-off filter to the image sensor are transmitted to the center region and the plurality of edge regions.

26. An iterative color shading estimation process comprising: obtaining a plurality of hue components from scene statistics of a captured image, wherein the scene statistics represent a downsampled version of the captured image; initializing an iterative problem of solving for a color shading component value and an intrinsic color component value, the color shading component representing a gradient of variation in color response across the captured image, the intrinsic color component representing a hue content of a scene represented by the captured image; performing a first iteration of the iterative problem; determining whether the color shading component value and the intrinsic color component value have converged; and if the color shading component value and the intrinsic color component value have not converged, performing an additional iteration of the iterative problem, and, if the color shading component value and the intrinsic color component value have converged, outputting the color shading component.

27. The iterative color shading estimation process of claim 26 , wherein performing a first iteration of the iterative problem comprises solving for the color shading component value using a fixed intrinsic color component value.

28. The iterative color shading estimation process of claim 27 , wherein performing a first iteration of the iterative problem further comprises solving for the intrinsic color component value using a fixed color shading component value.

29. The iterative color shading estimation process of claim 27 , wherein performing a first iteration of the iterative problem further comprises solving for a plurality of partial gradient values using the fixed intrinsic color component value.