Image demosaicing taking account of chromatic aberration
A method of chromatically-corrected image demosaicing for a sensor with a colour filter array (CFA) such as a Bayer filter array. The demosaicing makes use of local chromatic aberration correction data to determine chromatically-corrected pixel positions for spatial interpolation. In implementations a chromatically-corrected quadratic adjustment is also applied.
1. A method of chromatically-corrected image demosaicing, the method comprising:
inputting, to a processor by an image sensor comprised of light sensitive pixels, image data comprised of pixel values for the pixels;
determining, by the processor when demosaicing the image data, the pixels neighbouring a targeted one of the pixels;
compensating, by the processor when determining the pixels neighbouring the targeted one of the pixels, chromatic aberration of an image processing system comprised of the image sensor and the processor;
obtaining, by the processor when spatially interpolating between the pixel values for the pixels neighbouring the targeted one of the pixels, a colour value for the targeted one of the pixels; and
adjusting, when demosaicing the image data, the colour value dependent upon an image brightness variation in a region around the targeted one of the pixels,
wherein adjusting the colour value comprises:
determining an adjustment to the colour value and scaling the adjustment dependent upon a distance between the targeted one of the pixels and one or more of the neighbouring pixels compensated for chromatic aberration.
2. The method of claim 1 , wherein the region around the targeted one of the pixels comprises a local region of the colour filter array.
3. The method of claim 1 , wherein the image brightness variation is defined by a set of colour values for a set of the pixels in the region each covered by a filter of a filter colour.
4. The method of claim 1 , wherein the adjustment is dependent upon or substantially equal to a linear combination of one or more functions of the chromatic position correction,
the method further comprising:
determining one or more coefficients of the linear combination from the colour values.
5. The method of claim 4 , wherein the one or more functions of the or each chromatic position correction are quadratic functions of the or each chromatic position correction.
6. The method of claim 4 , wherein the one or more coefficients comprise linear combinations of the colour values.
7. The method of claim 1 , wherein adjusting the colour value dependent upon an image brightness variation in a region around the targeted one of the pixels comprises:
performing a convolution over pixel values in the region around the targeted one of the pixels.
8. The method of claim 1 ,
wherein the colour filter array is a 2D array defining a 2D pattern of colour filters, wherein the neighbouring set of pixels comprises a set of pixels in two dimensions, and
wherein determining the adjustment comprises:
determining first and second partial adjustments representing the image brightness variation in each of two orthogonal directions in the array, and
combining the first and second partial adjustments to determine the adjustment.
9. The method of claim 1 wherein the colour value is green.
10. The method of claim 3 ,
wherein the colour filter array comprises a Bayer filter, and
wherein the filter colour is green.
11. The method of claim 1 ,
wherein the neighbouring set of pixels comprises a set of four pixels, and
wherein the spatial interpolating comprises bilinear interpolation.
12. A method of chromatically-corrected image demosaicing, the method comprising:
inputting, to a processor by an image sensor comprised of light sensitive pixels, image data comprised of pixel values for the pixels;
determining, by the processor when demosaicing the image data, the pixels neighbouring a targeted one of the pixels;
compensating, by the processor when determining the pixels neighbouring the targeted one of the pixels, chromatic aberration of an image processing system comprised of the image sensor and the processor;
obtaining, by the processor when spatially interpolating between the pixel values for the pixels neighbouring the targeted one of the pixels, a colour value for the targeted one of the pixels; and
adjusting, when demosaicing the image data, the colour value dependent upon an image brightness variation in a region around the targeted one of the pixels,
wherein adjusting the colour value dependent upon the image brightness variation in the region around the targeted one of the pixels comprises:
adjusting the colour value dependent upon an estimated second or higher partial derivative, with respect to position, of a set of colour values for a set of the pixels in the region each covered by a filter of a filter colour.
13. A method of chromatically-corrected image demosaicing, the method comprising:
inputting, to a processor by an image sensor comprised of light sensitive pixels, image data comprised of pixel values for the pixels;
determining, by the processor when demosaicing the image data, the pixels neighbouring a targeted one of the pixels;
compensating, by the processor when determining the pixels neighbouring the targeted one of the pixels, chromatic aberration of an image processing system comprised of the image sensor and the processor;
obtaining, by the processor when spatially interpolating between the pixel values for the pixels neighbouring the targeted one of the pixels, a colour value for the targeted one of the pixels; and
adjusting, when demosaicing the image data, the colour value dependent upon an image brightness variation in a region around the targeted one of the pixels,
wherein adjusting the colour value dependent upon the image brightness variation in the region around the targeted one of the pixels comprises:
adjusting the colour value dependent upon a linear combination of quadratic functions of two spatial coordinates, with coefficients given by estimated second partial derivatives of the colour values with respect to the spatial coordinates.
14. A non-transitory data carrier carrying processor control code to implement the method of claim 1 .
15. The method of claim 1 , wherein compensating the chromatic aberration comprises:
determining a chromatically-corrected position of the targeted one of the pixels.
16. The method of claim 15 ,
wherein determining the chromatically-corrected position of the targeted one of the pixels comprises:
adjusting a position for each of the pixels in the region by a chromatic position correction dependent upon the chromatic aberration, and
wherein the adjusting comprises:
determining an adjustment from the filter colour,
modifying the adjustment using the chromatic position correction for each chromatically-corrected pixel position to determine a modified adjustment, and
applying the modified adjustment to the colour value.
17. The method of claim 15 , wherein determining the chromatically-corrected position of the targeted one of the pixels comprises:
applying x- and y-offset values to a position of the pixel.
18. The method of claim 1 , wherein compensating the chromatic aberration comprises:
ascertaining, when determining the pixels neighbouring the targeted one of the pixels, chromatically-corrected positions for each of the pixels neighbouring the targeted one of the pixels.