Removing Chromatic Aberrations with Photoshop

By Jill Smith

Notice the chromatic aberration along the arms.

Chromatic Aberrations are those ugly, coloured halos that may outline contrasted edges in an image.  They are often bright blues and yellows, or magentas and greens.  The colours of light (yes, white light is made up of colours; all the colours of the rainbow - same principles apply), don't all behave and bend the same way.  That is why we get to see and enjoy rainbows (nice), but also why we have these gross distortions (not so nice).   Here are two quick and dirty ways to banish them (one way is quicker and dirtier than the other, but it may not always be the answer).

 Method 1

RAW images - If your images have been shot in RAW file format, they may be opened in Camera Raw, and possibly corrected very easily there.  Go to the Lens Corrections tab, and click the “Remove Chromatic Aberration” box at the top of the panel.  Most of the time this will do a good job.  That was easy.

 Method 2

The following Chromatic Aberration Removal technique may be employed in the event that the Camera Raw feature did not completely remove the aberration, or if there is no RAW image to work with.

This image sports arguably the most grotesque chromatic aberration I have ever seen.  Notice how the distortion becomes more severe further away from the centre of the image.  The distortion here is so terrible for a couple of reasons:

1. Using a flat port increases both the refraction and radial distortion of light underwater. All wavelengths of light (coloured light) do not bend and behave exactly the same way when transitioning from water, through glass and then air, and this is obvious to observe along high contrast edges within the image.The dome port I have since added to my underwater photography kit significantly decreases these distortion effects.
2. The subject/s were strongly backlit and under-exposed, and the extreme contrast of the edges resulted in some pretty hefty aberrations. Adjusting the contrast and brightness of the image only worsened the problem.
   

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The Steps

• Open the Image in Photoshop
• Duplicate the layer (Ctrl J for PC, Command J for Mac).
  

• With the top layer activated go to the Menu Bar > Filter > Blur > Gaussian Blur.
• The Pixel Radius selected in the Gaussian Blur dialogue box will depend on both the resolution of the image, and the severity of the chromatic aberration.  For this image, I used a Radius of 20, which is much higher than I have ever used before.Start with 10 or 12, and look at the worst areas of distortion in the image.  If you can still see strong purple or green highlights along the edge, you may need to increase the Radius until the aberration colours are not recognizable.  I find I use a Radius of 12 to 15 most of the time.  Once you have decided on the degree of blur, click OK.
  

This part of the process will be numbered to correspond with the figure below.

1. Add a Layer Mask - If you just click the "Add a Layer Mask" icon by itself, you will have a white mask showing the entire blurred layer.  However, that is not exactly what we want. We want a black layer mask to hide the entire blurred layer, and we will "paint in" the areas we wish to correct.  To do that, hold the Alt key down while you click the "Add a Layer Mask" icon. 
   
2. This is the black "Hide All" layer mask, and now we cannot see any of the blurred effect on the layer we just created.
3. This is a layer blending option.  It defaults to normal.  Click the drop-down menu to reveal a list of options.  Select "Colour" for your blend mode.  (this says to Photoshop, "Keep the colour information from this layer, and the detail from the bottom layer."
4. Click on the brush tool from the tool bar.
5. Make sure your foreground is set to white.

• Now we are ready to "paint away" those ugly aberrations. With your brush selected, adjust the brush size to be not much bigger in diameter than the thickness of the aberrations.  Brush size may be adjusted from the options bar across the top of the desktop, and the hardness should be set to 0% so that the brush effects are feathered.
  
• You will notice that the black mask is still active (there is a box around it to indicate that you are painting in the mask, not in the actual image).
  
• With the small white brush, "paint" over the aberrations in the image, and watch them disappear!
  

Brush Options are circled at the top. Now just carefully "paint away" all that ugly!

After painting away the aberrations

What that section of the mask looks like after painting with white

While the nasty colours have been taken care of, this particular image (and this section taken near the edge) was an extreme example, and I can still see the contrast on the edges.  If I first ran this image through Camera Raw and checked the "Remove Chromatic Aberrations" box, they would have been largely removed, and the above method would have cleaned the rest up beautifully....but for this method, we wanted to work with the worst case scenario. 

Happy Shooting and Editing!