On Thu, Apr 01, 2010 at 01:33:32AM +0100, Owen Pearse wrote: > As far as I am aware a true radial PSDF should be invariant under rotation > of the original image data. > > However the rPSDF in Gwyddion doesn't seem to be invariant under rotation, > which I tested using Gwyddion's "rotate by arbitrary angle" feature > (Gwyddion v2.19 on WinXP). > > >From what I can gather from the code, it seems to only include the FFT data > from the first quadrant only, ignoring the other 3 quadrants, hence the > change in rPSDF under rotation. > > Specifically lines 2273-2274 & 2277 from: > http://gwyddion.svn.sourceforge.net/viewvc/gwyddion/tags/gwyddion-2.19/libprocess/stats.c?revision=10808&view=markup > <http://gwyddion.svn.sourceforge.net/viewvc/gwyddion/tags/gwyddion-2.19/libprocess/stats.c?revision=10808&view=markup>seem > to indicate that only the first quadrant is being used, ignoring the rest.
It seems you are right, it is necessary to use a half of the 2D DFT output, not just a quarter. I have to look into it. Yeti ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
