Noise reduction with GMIC (gimp plug-in)
Did some tests with the GMIC plug-in for GIMP and I think it works quite well for a freeware tool.
First I applyed one of the GMIC denoise filters and then merged the result 50% to the original image. So what you see here is not the ultimate result but only one of my trials. GMIC contains a lot of different noise reduction algorithms with tons of settings. GMIC even allows you to apply the nr to individual color channels only. This leaves room for some experiments. But it's rather a tool for the patient ones among you.
Both shots at 6400 (ISO equiv). Original is a RAW file with high ISO NR turned off. Actually Nikon states that at ISO 6400 there is always at least a little bit NR active. Turned off default NR in NX2 too.
|Blue and yellow in water by fireplace33|
from Ink and water
|Kylmä joki kopio by Kaappo|
from Shutter speed 1/25 or slower
|WR_2.8_13 copy copy by photoprof|