Removing chromatic aberrations
Chromatic aberration occurs when the camera records incorrect colors within the image. In conventional film cameras, chromatic aberration is usually caused by a lens defect. In digital cameras, several factors can contribute to chromatic aberration, including the following:
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The inherent lens aberration in the camera may cause fuzziness at image edges. Photos taken with telephoto and zoom lenses are more prone to contain chromatic aberrations because of the way in which digital cameras capture light rays far from the optical axis.
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The auto-exposure feature of the camera, which estimates the correct exposure setting, may cause sensor blooming.
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Different colors may be caught by different camera sensor elements, and they may combine to make one pixel. This process is called demosaicing.
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Activities such as artifact removal, noise removal, and sharpening may occur inside the camera after processing.
In your own digital photos, you may notice chromatic aberrations in photos with the following content:
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the sky seen through tree branches or leaves
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the edges of interior doors or windows through which bright light enters
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fireworks or city lights
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fluorescent light fixtures or bare lightbulbs
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sun or light reflections on water
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the edges of backlit objects
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sunlit white shirts against a dark background
After identifying these types of color defects, you can reduce or eliminate them.
To remove chromatic aberrations from a photo
1
Choose
Adjust 
Chromatic Aberration Removal.
The Chromatic Aberration Correction dialog box appears.
2
Ensure that the Before and After panes are visible at the top of the dialog box.
3
Set the zoom control in the dialog box to at least 200%.
The zoom control is located below the Before and After panes. Zooming to 200% helps target the problem areas in the photo.
4
Click the
Pan button
, and pan the image to set a viewable image area in the Before pane.
5
In the Before pane, drag to define the area needing correction.
Note: The area needing correction is called the sample box. You can create up to 10 sample boxes. Each sample box is represented as "Sample
n" (where
n is a number from 1 to 10) in the
List of Samples area in the center of the dialog box. Each sample listing has a color swatch to the left, indicating a color average for the sampled area.
6
Choose a sample entry from the
List of Samples area.
7
Type or set a value in the
Range control to determine the color range of the active sample, which affects the pixel range to be corrected.
The range you specify is represented in the color box directly above the
Range control.
8
Type or set a value in the
Radius control to determine the size of the sample’s aberration.
Note: The default value is 10. Values from 4 to 20 usually produce the most acceptable results. Values greater than 10 are useful on sampling areas that enclose sensor blooming aberrations. Values less than 10 are useful when you are removing 1- or 2-pixel aberrations caused by demosaicing, as well as when you are working on images of less than one megapixel. Set the
Radius control to the smallest setting that effectively removes the aberration.
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Drag a sample box handle. |
Delete a sample box button in the dialog box |
Click a sample box, and click Remove. |
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Drag a corner onto its diagonally opposite corner, and stop dragging when the corners meet. |
Display the affected image areas |
Mark the Show Differences check box. The affected areas appear in the After pane as white areas on black. Brighter areas represent greater degrees of correction. |
Preview the results on the image |
Mark the Show Differences check box, and make sure the Preview on Image check box is marked. |
To create more than 10 sample boxes, you can apply the corrections and then restart the effect.
You can automatically create a new layer on which the corrected image resides by marking the Result on New Layer check box. This option protects your original image on its own layer. If you do not mark this check box, the corrections are applied on the same layer as the original image.
You can limit the number of "false corrections" by making a selection and then marking the Result on New Layer check box. You can also use this command on separate layers of an image.