Fix water chromatic aberrations. Align RGB channels

Hello, I took some pictures of an aquarium and I discovered that there is a lot of chromatic aberrations because the interface between the water and the air/tank glass. The solution I think is to roughly displace the RGB channels independently and I was able to improve it a bit by using retouch in clone mode and with “RGB blue channel” blend mode, see the screenshot for comparison (my fix with retouch is in the bottom, chromatic aberrations module is disabled in both cases). There is still room for improvement, I should move also the red or green channel

I don’t know if I’m missing something but I think this is a problem that happens 0.1% of the time but any kind of rough fix can make HUGE improvements in the image.

  • Is there a better way to do this in Darktable? It is very hard to use retouch for this, since I have to use a circle in max size and its very hard to align the colors blindly by hand since I cannot see the result in real time.

  • Would it make sense to create a module to fix huge chromatic aberrations by aligning channels by hand? I also had this problem when capturing images through a telescope (the term is digiscoping). I would like to contribute programming a module, although I should think if it makes more sense to extend an existing module, think about the best way to do it (which spatial transformations apart from translation would be needed?), and anyway in the next 4 months I dont know if I have time

If any developer sees this, thank you for the program! I love it

Some good suggestions here…I think the recomendation is to start in the lens corrections with some manual TCA correction and go from there…all explained here…

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Keep in mind that the fringing in the aquaruim photos isn’t due to lens imperfections, but to diffraction at the glass and water (think of a prism). That means that it’s dependant on the viewing angle (no diffraction if you are perpendicular to the glass). The viewing angle can vary a lot within one image when using a wide-angle lens, in a way that depends on the camera position relative to the glass. So your alignment of color channels will have to be local, no global formula…

In the case of digiscoping, it is the lens that’s in cause, so the (three) existing modules might be enough…