I’ve been using the GIMP image editor (also known as the GNU Image Manipulation Program) (also known as the wonderful, open source, free photo editor with the awful name) a lot lately. Version 2.4.2. I highly recommend a second look if you haven’t tried it recently. The newest version has vastly improved controls for cropping and selections, a foreground selection tool, a healing tool, and better brush management among other enhancements.
But one thing my stock GIMP install didn’t have was a decent noise removal filter. That is, until I downloaded and installed the GREYCstoration plugin. Installing it is as simple as downloading and dropping the plugin into the GIMP plugins directory. Restart GIMP and you’ll find a new menu under Filters | Enhance | GREYCstoration.
The filter provides a ton of options for fine-grained control of the noise removal process but comes preset with what seem like very good defaults. What follows are a sample ISO 1600 image shot with my D70 followed by several 100% crops with different levels of noise removal applied. I left all of the default settings and just changed the Strength slider as indicated (strength ranges from 0 to 200):
Sample image, 1600 ISO, cropped areas highlighted
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100% crop — no noise removal
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Strength: 25

Strength: 75

Strength: 150
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100% crop — no noise removal
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Strength: 40
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Strength: 80
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Strength: 120
In my opinion, the plugin works extremely well, maintaining a good balance between noise reduction while retaining overall image sharpness. As you can see, the filter seems to work best at lower strength values between 20-75. Keep in mind though that these are 100% crops and images are much more forgiving when viewed at normal sizes (for example, as a framed 11×14 at 3 feet distance). The higher strength values reveal another use for noise removal: photographic youth restoration.
Both GIMP and the GREYCstoration plugin work with Windows, Mac, and Linux.
Wicked, thanks for sharing the nice find, John!