I received an email from David Tschumperlé (interview, web) the author of GREYCstoration (blog), introducing G’MIC, GREYC’s Magic Image Converter. GREYCstoration’s capabilities (read: algorithms) have been moved to this new high potential framework: all the operations are now filters written in an easier-to-program macro language (gmic). That makes it more simple to add new custom made filters while retaining the power and infrastructure of G’MIC.
G’MIC is available here as a command-line tool or as a GIMP plug-in.
Among the 50+ filters available, you will find mirrors and tiles effects, a fish eye effect, quite a few painting effects (pen drawing and BW pencil being my favorites), and so on. I am not a great fanboy of filters – you either have a good enough image that defends itself or not and no amount of filtering will change that, IMHO.
However G’MIC offers 2 filters of the utmost photographic interest (and I chose my words): 2 denoising methods – anisotropic smoothing and patch-based smoothing. They are on par with the best commercial software available – at the cost of more parameters to set and longer time processing, though. The most recent patch-based method already reduces the amount of parameters to set while keeping a high quality output.
Just for the record, here is a quick test from my favorite noisy image:
Removing Red and Blue noise (so keeping my favorite grain-like output) with the anisotropic filter:
And the same with the patch-based filter:
As David mentioned, it is hard to objectively judge denoised output. The above example is not a full blown test, just an illustration of what is possible. Sill G’MIC is very interesting if you need a high-quality opensource noise removal tool.
All of these filters are neatly put in a GIMP plugin with sliders and instant preview, as shown in this screenshot:
Once you are happy with your settings, you can turn to using the command line tool (gmic) which offers higher bit-depth results. Be warned, though, that this will take a lot of computing power – so make sure your settings are correct!
If you are interested in this tool (and you should 🙂 ), you can get it from G’MIC’s Sourceforge repositories. Various pre-compiled versions are available, but if you need to compile GMIC from scratch, beware: it will bring your computer to its knees! To use the GIMP plugin, simply copy gmic4gimp to your GIMP plugin directory, restart GIMP and voilà, the plug-in is available at the bottom of the filter menu.