GIMP and selective noise reduction

[Mark L]

Is there an easy way to do NR for BGs using GIMP. I'm thinking of birds but selective NR is a good place to start.

[REV]

Thanks Mark,I am keen for some relies..

Cheers Rev.

[tduell]

Is there an easy way to do NR for BGs using GIMP. I'm thinking of birds but selective NR is a good place to start.

Hello Mark,
I'm not an active GIMP user as darktable provides this and more...and is easier to use, but I did note that the latest development version of GIMP (2.9.4) has improved selection tools, and I would assume one could use a selection with other tools, such as NR. GIMP 2.9.4 also works with 16 bit so that would be another plus. GIMP 2.9.4 is available for Linux, not 100% sure about Windows (you use Windows don't you?) but would expect there are Win builds available.
I really should try to come to grips with GIMP as it does provide a few tools that darktable doesn't.
If you have a fiddle around with this let's know how you get on.

Cheers,
Terry

[fillum]

Mark, I don't use GIMP but a quick search indicates that it has layers and layer masks.

What I typically do in PS for any (non-trivial) selective adjustments is use a separate layer with a layer mask. So in this case I'd duplicate the layer, apply NR on the duplicate layer, and then use the layer mask to allow only the background areas of the NR layer to show through. How good this looks will depend on the selection/masking tools available and your skills in using them (brushes etc). The advantage of using layers is that you can come back later and alter the masked area, or even reduce the amount of the effect by reducing the layer opacity. [In PS you can also use smart-objects / smart-filters to come back later and alter the amount of the effect, but I don't know if these are available in GIMP].

Although occasionally, if I just want to clean up a noisy sky for example, I'll just run the blur tool across it a few times using low settings.

The other side of NR is sharpening. If you have an image with a noisy background it is usually best to apply selective sharpening to your subject only so that you aren't making the background noise worse by sharpening it. If you shoot raw and do sharpening / NR in your raw converter but it doesn't allow selective adjustments, you can create two output files - one optimised for a sharp subject and the other optimised for an NR'd background - then load these into separate layers in GIMP and apply layer masks to combine the best of both files.

Finally there are third-party options such as Nik DFine (for NR) and Sharpener Pro which allow selective adjustments. From what I can gather these work in GIMP but I don't know how smooth the workflow would be. Nik plugins are free btw...



Cheers.