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.
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):
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.
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.
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.
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):
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.
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.
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!