GIMP/Imagemagick Noise Removal with Median Filter

Photoshop users have had at their disposal a method of combining layers using a mathematical median function, and now the F/OSS users can use the same method to remove noise from static images!

To illustrate, here is an image of mine shot on my OM-D E-M5 at ISO 25,600:

1/100 second, f/8, ISO 25,600

 This is a great method for reducing noise in images that are static scenes.  All it requires is for the images to be properly aligned, either through a tripod, and/or using software in post.

And Imagemagick or G'MIC for GIMP.

Here are some side-by-side 100% crops to illustrate:

These results were obtained from simply median blending 10 images of the same scene.  For details on how it's done, head on over and read the rest of the article:

Noise Removal in Photos with Median Stacks (G'MIC/GIMP & Imagemagick)