Chromatic Aberrations – Learn how to remove them from your images
Bird With Chromatic Aberration Twig

Chromatic Aberrations – Learn how to remove them from your images

Beginner’s guide for dealing with Chromatic Aberrations

If you look up what Chro­mat­ic Aber­ra­tion is, and you end up on the Wikipedia page for that search term, you are quick­ly over­whelmed by optic tech­ni­cal terms. But don’t dis­miss the top­ic because of that, as Chro­mat­ic Aber­ra­tions do not care if you under­stand them or not. They can spoil your images and you might want to remove them. The good thing is that mod­ern soft­ware makes it an easy task.

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What is Chromatic Aberration?

It is a lens issue. When the light pass­es the lens, dif­fer­ent col­ors pass through it in a slight­ly dif­fer­ent way, caus­ing them to land in a dif­fer­ent spot on the sen­sor than where they should be ide­al­ly. 
If I short­en one sen­tence on that Wikipedia page, you can read it this way: “Chro­mat­ic aber­ra­tion (CA) […] is a fail­ure of a lens to focus all col­ors to the same point.”

How does that look like in my image?

Let us start with this sam­ple image here (screen­shots are tak­en from with­in Adobe Lightroom):

Botanical Garden Tree, Christchurch, New Zealand - with Chromatic Aberration lens issue
Botan­i­cal Gar­den Tree, Christchurch, New Zealand – with Chro­mat­ic Aber­ra­tion lens issue

I marked the area in which I would expect CA to hap­pen. It is usually

  • at the bor­der of the frame
  • bright back­ground with a large con­trast to the sub­ject (twigs)
  • shot with a wide-angle lens (this was 21mm on a crop sen­sor camera)
  • and aper­ture is wide open (f/3.5)

We need to zoom in to the marked area to see what the Chro­mat­ic Aber­ra­tion looks like.

mostly purple fringing

If you have a less than per­fect lens — that is always the case to a degree — then high con­trast details around the edge of the frame have more or less pur­ple or green (or both) fringes.

You expe­ri­ence that effect also more towards the mid­dle of the image if you shoot wide open (low f/number). The lens design­ers have to fight two types of CA, and it is dif­fi­cult to elim­i­nate both, even if they use expen­sive glass and com­plex com­bi­na­tions of lens elements.

Note: The col­or fring­ing you see in the image can also result from an effect called “bloom­ing”, which is not a lens issue, but caused by too much light per pix­el on a sen­sor. The cause of the col­or fringes does not make any dif­fer­ence in how to remove it with soft­ware in post-processing.

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What can we do?

Most of the time you can avoid an issue at the time of the image cap­ture. That is the bet­ter option. If that fails, use post-processing. 

Things you can try when taking the image

  • try to avoid big con­trast with light back­ground at the edge of the frame
  • if the dis­col­or­ing hap­pens on an impor­tant part of the image, try to get that more cen­tred (if that makes sense for your image)
  • stop down (use a big­ger f/number)
  • use a dif­fer­ent focal length if you use a zoom lens

Often you don’t want to use any of that because it would change your image com­po­si­tion. Or you just didn’t notice the Chro­mat­ic Aber­ra­tion. Then Plan “B” comes into play.

Things you can try when it is too late

Some cam­era man­u­fac­tur­er have inbuilt soft­ware to remove CA as much as pos­si­ble. If that didn’t work, you can use most mod­ern image pro­cess­ing soft­ware. I’ll show you how it works in four unique programs:

  • Adobe Light­room (or Adobe Pho­to­shop Cam­era Raw module)
  • Affin­i­ty Photo
  • DxO Pho­to­Lab
  • Sky­lum Lumi­nar 4

They all do an excel­lent job and can auto­mat­i­cal­ly remove most of the CA, but there are dif­fer­ences in han­dling and result (and price).

You might also use Gimp (with an add-in) or Pic­ture Win­dow Pro 8, both are free. I have not test­ed the add-in or Pic­ture Win­dows Pro 8 yet, but the lat­ter is on my list to check out. Looks inter­est­ing for a free software.

When you watch the ani­mat­ed GIFs below, keep in mind that they illus­trate the process, but the col­or palette is reduced, so you can’t judge the result qual­i­ty from that.

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Adobe Lightroom

You’ll find the Chro­mat­ic Aber­ra­tion cor­rec­tion in the “Devel­op” Mod­ule > Lens Corrections.

If tick­ing the “Remove Chro­mat­ic Aber­ra­tion” box does not yield the desired result, you can try to help the sys­tem find fringe col­ors. Go to the “Man­u­al” tab and select the col­or. Watch the ani­mat­ed GIF below (know that the ani­mat­ed GIF does not record all col­ors as in actu­al life, take it as a “How To”, but not to judge the qual­i­ty of the result):

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Affinity Photo

I like the process with Affin­i­ty Pho­to as it lets you use the split screen to com­pare the results. You can also do man­u­al adjust­ments, just watch the ani­mat­ed GIF below.

 

AffinityCARemove
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DxO PhotoLab

DxO Pho­to­Lab is always a good choice when remov­ing arte­facts caused by lens­es or lens-body com­bi­na­tions. It has an exten­sive data­base of these com­bi­na­tions and can cor­rect lens issues auto­mat­i­cal­ly. The “mag­ic wand” tool also seemed to work well in my exam­ple image.

DxOPhotoLabCARemove
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Skylum Luminar 4

Lumi­nar does not allow man­u­al mod­i­fi­ca­tions, so if the auto­mat­ic removal of the CA does not sat­is­fy you, you are out of luck. But it has the split screen I like.

There was also a weird bug when you first turn on the CA cor­rec­tion, it leaves the right side of the split screen blur­ry. It re-ren­ders once you turn it off and on again. 

Luminar4CARemove
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That’s it. Get­ting rid of the Chro­mat­ic Aber­ra­tion is a lot eas­i­er than to under­stand the physics behind it. 

If you see the green-pur­ple “ghosts” in your images, then you know now how to remove them. And you can boast with a new tech­ni­cal term at your next local pho­to club meet­ing: “Chro­mat­ic Aber­ra­tion”. Just switch the top­ic quick­ly if some­one asks you what it is. Unless you are an expert in optics.

Have fun tak­ing pic­tures — with­out pur­ple fringes!

Frithjof Moritzen

Photography Club Enthusiast

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