Ernst Lippe is the author of "refocus". Here is an excerpt from the author's description.
Refocus is a plug-in for the Gimp (the GNU Image Manipulation Program). This plug-in attempts to "refocus" the image, using a technique called FIR Wiener filtering. The traditional technique for sharpening images is to use unsharp masking. Refocus generally produces better results than unsharp masking.
Ernst Lippe [refocus.sourceforge.net]
I saw in log files that a number people attempted to publish patches on the sourceforge site, but for some reason the patch code does not appear to be available from sourceforge. There was a message that mentioned the problem I am providing a patch for, but I couldn't find the patch code.
Peter Heckert has adapted the plugin to work with gimp-2.2, and it also works with gimp-2.4. Peter's version of refocus is available from hphsite.de/refocus.
As I started using the "refocus" plugin on raw files from the Powershot A620, the plugin crashed. I figured out that the plugin crashed only for pictures of some peculiar sizes and not for picture of more typical sizes. I found the error in the source code and I publish here a patch to be applied to Peter Heckert's source.
I didn't find a way yet to update either the sourceforge site or the gimp plugin site so I resort to publish my path here.
tar xvzf refocus-0.9.0-gimp-2.2.tar.gz
cd refocus-0.9.0-gimp-2.2/;
patch -Np1 < ../refocus-0.9.0-gimp-2.2_rlx.diff
./configure
make
gimptool --install-bin src/refocus
# That's it.
Martin Egger is the author of SmartSharpen and he agreed to modify his script to use "refocus" as well as "unsharp mask". Martin's script can be downloaded from Plug-In: Smart Sharpen (Redux). Use the following command to install Martin's script. Then to use the script, open menu "Script-Fu/Eg".
gimptool --install-script Eg-SmartSharpen-refocus.scm
I typically use the plugin with the default parameters. I would increase the noise factor if I find that the plugin amplifies the noise too much. Otherwise, if I am working on a raw picture and the finished picture won't be scaled down, I might increase the radius to 1.3 or 1.5 to account for the alternance of colored pixels on the raw data (the real pixels are larger than implied).
If I am working with a raw picture that I want to downsize, I will apply the refocus plugin once on the raw picture (after any rotation) and before downsizing. Then I would apply the refocus plugin a second time just before saving the result.
I know that it is difficult to justify applying refocus before downsizing if refocus is to be applied later anyway, but I feel that the result is sharper when I do it that way than when I use refocus just once at the end.