Chromatic Aberration

The term chromatic aberration covers a number of different optical phenomena, all of which manifest as unwanted colored fringes round picture elements, particularly noticeable around high-contrast transitions in relatively neutral picture areas.

Lateral chromatic aberration is produced when optical distortion results in object points coming to a focus at different points in the image field, depending on the wavelength (= color) of the light. The result is a focused image spot that is displaced between the three (Red, Green, Blue) color channels. With ever-higher sensor resolution, lateral chromatic aberration is becomes increasingly visible, in turn making it more and more important to precisely address distortion for each color plane.

Longitudinal chromatic aberration occurs when the lens brings light from the object to a focus in different image planes according to its wavelength. The result is an image spot that is less sharp (= larger) from one color channel to another; to further complicate matters, there may also be differential astigmatism!

Both of these produce unwanted color fringes that are lens and setting dependent.


Lateral chromatic aberration	DxO Optics Pro Correction

(Sony F828)

So-called ‘purple fringing’ is a phenomenon caused by image sensor characteristics, which cause highlight areas to ‘spill over’ into adjacent pixels; the way color matrixing is performed means that this tends to produce a greater spill in the red and blue channels, leading to colored fringes in highlight areas that are predominantly purple in hue.


"Purple fringing"	Corrected by DxO Optics Pro

"Coma" describes the phenomenon where highlight areas produce a ‘halo’ effect that may be different between the three color channels.

Other causes of unwanted color artifacts may include, among other things, the particular demosaicing algorithm used in certain equipment.

DxO Optics Pro applies chromatic aberration in two ways:

a calibrated, lens-specific correction for chromatic aberration based on DxO’s unique modeling techniques (which works for supported lenses only)
and a non-equipment-specific correction for color fringes that may be caused by lateral chromatic aberration, purple fringing, demosaicing errors, etc.

The first correction takes place as part of DxO’s distortion and sharpening algorithms, where the calibrated corrections are applied to the three color channels independently, which is a good solution for the equipment-dependent errors, where camera/lens support is available.

A second level of correction, which is available for all images (irrespective of having the appropriate DxO Correction Module), makes it possible to also correct for those phenomena that are picture-content dependent. This works basically by suppressing differences between the color channels where these are associated with large luminance transitions in the image.

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