Chromatic aberration is the color fringing you often see when a hard-edged building or rock is backlit by the bright sun. It’s an optical limitation of the lens. High quality lenses, smaller apertures, and “remove chromatic aberration” in Lightroom all help significantly. The tool in Lightroom is so good that I leave it check for all of my images (I’ve never seen any drawbacks). But even with all the right tools and technique, you are still likely to run into some chromatic aberration that cannot be removed in the RAW file.
In those situations, Photoshop can remove any remaining problem. Chromatic aberration is mostly a color problem, so replacing the color is the key to fixing it. There are a couple of different ways to do this, and each approach has its merits.
Technique #1: Gaussian Blur
Blurring the image is often a very effective way to smear the neighboring colors across the color fringe. To use this approach, simply duplicate your layer, set it to color blend mode, and apply a small amount of Gaussian Blur (just enough to fix the problem, 2-3 pixels is usually great). This should fix the edges nicely, but might cause problems in other parts of the image. So it’s best to add a black layer mask and paint white over the edges to reveal the correction only where it’s needed.
There may still be a few issues at this point. If you wish to further target the blur layer, try the following:
- Switch the blend mode from color to “hue” to see if that improves the results.
- If you see haloing, use quick select, light luminosity selections, or BlendIf to hide the sky area in the blurred layer (If you have Lumenzia, trying using “not L2-L4” BlendIf masks to get rid of halos).
- If you have Lumenia, try using the color masks to target red/green if you wish to paint precisely over those areas. This can help avoid issues on both the light and dark side of the edge.
- If you still see issues in the dark area, try the next technique…
Technique #2: Paint in new color
If the Gaussian blur doesn’t work, or the color fringe is affecting too much of the original edge, you may get better results simply by painting on the color you need. You can sample the desired color from neighboring pixels and paint it onto the blurred layer created above – or paint on a blank layer set to color or hue blend mode. This approach is often best used as a way to refine any remaining issues from the first technique, if needed.