I am having a challenge with chromatic aberrations. The image has a blown out sky, and sharp contrast between several objects and that sky. For the lens I used (Canon EF-S 18-135mm f3.5-5.6 IS USM) lensfun contains correction data (for distortion and TCA). In a part of the image the TCA is removed (first image below), in another part it isn’t (second image below).
I tried some combinations of the lens correction, defringe and chromatic aberrations modules. I could not find a combination that works for the whole image.
The out of camera JPG (see below) also shows a lot of chromatic aberrations, and also distortion. In camera correction was enabled, and it recognised the lens, so I don’t know what went wrong there.
Here are the raw image (23,8 MB), and 1:1 crops of the various module combinations I tried. crops.zip (13,2 MB)
What are the best options to get rid of the chromatic aberrations?
Because vignetting data is missing in lensfun for this lens, and I have another lens that is missing completely, I am planning to create correction data, and upload it to the lensfun project. Maybe that will give better results. But I will have to wait until the weather clears up a bit.
Here’s a quick try using the default setting of the defringe module along with a trick I learned from Steve Perry’s Youtube channel. For the nasty purple fringe on that ibeam I used the lowpass module to apply enough blur until you cannot notice the fringe anymore then change the blend mode to “color.” That by itself will mess up a lot of the other colors, so then I applied a drawn mask on the affected area. Hope this helps you out.
I’ve never really given Rawtherapee much of a try. So I tried what you did in Rawtherapee 5.5 using the CA sliders and the defringe on. Although I couldn’t get exactly what you did, it was certainly better than my trick in Darktable. I’ve never got a good result using Darktable’s CA module and would usually use mulitple instances of the defringe module and/or the trick with the lowpass blur with the color blend mode. This was a learning experience. Thanks!
@sls141 Just use his *.pp3 sidecar to see what he did. One thing that you might not know is that “neutral profile” makes all of the settings neutral and generally unappealing, but it is a good way to test and learn what each tool does after everything is set to zero so to speak. Also turn to RT’s manual for more insight: RawPedia.
This is my try to correct CA with Darktable. I wasn’t able to fix it completely, maybe it has something to do with the overexposed areas, they are even overexposed in the RAW.
On the left side of the image the corrections were quite OK.
Thanks for all the response. More than I expected.
I am just a beginner with darktable. I will go through the answers and try the tips.
I did find some Youtube channels on darktable (Bruce Williams, Harry Durgin, Robert Hutton). I will add Steve Perry to my list.
I know that the sky is overexposed, even in raw. (I have pictures taken from the other side of the red building, showing a blue sky with white clouds.) It was the strong fringing that made me experiment with it.
