After my supervisor jokingly meantioned that I could clean up some micrographs using fourier transform, I thought I might give it a quick go, knowing that this was possible using gimp plugins, and after having some past experience in installing other plugins for the gimp. This is something that is made easier after the stable release of debian now includes gimp 2 rather than gimp 1.3.
A search for ‘gimp plugin fft debian’ lead me to a useful blog postFFT on images, and The GIMP by kstars. Following kstars advice I downloaded from here, i’m not sure I successfully compiled the binaries in the source package, however it seems to already include the necessary binaries.
There is also detailed description of how to remove coherent noise using GIMP in the The GIMP wikibook.
The image before processing.
The fourier transform of the image, after manual blurring, position indicated by arrows.
The image after processing, periodic lines removed, cracking is more clearly shown.
Larger versions of the images can be seen at the followingLink. So as we can see, a Professor knows that is it OK if he leaves periodic scratches after polishing, because his students can remove them by image processing.