a8 November 2012

Tutorial: dealing with chromatic aberration

This is a photo from 2011 taken in Masuria, Poland. This photo had some serious problems with chromatic aberration. I removed it using method described by the end of this tutorial.
What is chromatic aberration? Wikipedia defines it as:

"In optics, chromatic aberration (CA, also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength.".

Probably this description does mean much to you. Putting it simply chromatic aberration manifests itself as colour fringing (usually magenta, red, green or blue) on the boundaries between dark and bright areas of the photo.

Take a look at the close up of the above photo (before it was processed):

Can you notice ugly fringing (cyan and red) around the tree trunk, branches and leaves? It is what chromatic aberration is in practice.

Each lens produces some chromatic aberration but some lenses produce more and some less (generally speaking better lenses produce less of it). As I said it appears on the boundaries between regions of different brightness. So the natural solution would be to avoid shooting contrasty scenes but it would be very limiting at the same time. Fortunately we don't need to do this as we can reduce (or sometimes eliminate) chromatic aberration in post-processing.

Almost each software gives you an option to reduce chromatic aberration and also each software approaches this issue slightly differently so I will mention a few of them:

Photomatix Pro

In Photomatix Pro after selecting bracketed photos check "Reduce chromatic aberrations" box in the Preprocessing Options dialog. It does great job most of the time.


In Lightroom 4.1 select your photo and switch to Develop module. Scroll the right panel down until you see the Lens Corrections settings. Expand them and switch to the Color tab:
Lightroom 4.1 gives you 2 options to reduce chromatic aberration:
  • automatic,
  • semi-manual.
To use the first one just make sure to check "Remove Chromatic Aberration" checkbox. It does quite well but there are cases when it fails.

In such cases you can defringe using semi-manual setting. What you need to do is to tell Lightroom what is the colour of fringing. Click on the colour picker icon and select purple or green colour in your image that represents chromatic aberration. After you click on them Amount and Hue sliders will be set accordingly. You can also adjust the sliders manually - it is especially useful when Lightroom doesn't detect colour you clicked as purple or green (or you don't agree with its choice of settings :) ).

Note however that for large values of Amount colours of the whole image might be affected. For this reason I usually try to keep it below 4.
Adobe Camera Raw

Adobe Camera Raw is very similar to Lightroom so I will skip it here.

Manual chromatic aberration reduction

If everything else fails I reduce chromatic aberration manually using Photoshop:
  1. Open  image in Photoshop CS.
  2. Add new Hue/Saturation Adjustment Layer.
  3. Select color representing fringe (most of the time red, magenta, blue or green).
  4. Reduce Saturation and Lightness for it so it becomes invisible.
  5. Edit layer mask to make sure that Adjustment Layer is applied only to affected regions (you don't need to alter all colors in the image). Usually you will use soft brush and paint with white on the areas between bright and dark parts of the image.
For the image from this post, I reduced lightness and saturation of cyans, greens and reds around the tree trunk and the leaves. After this step the crop from the beginning of this post looks like this:

And the layer mask used by Hue/Saturation adjustment layer like this:

Post a Comment