Let's verify if I've understood: if I have a line long 1000 nm, scanned with 256 points, then I'll have a pixel of approximately 3,9 nm if I choose a cut-off of 0,12 It means that I'm cutting informations taken with a step more than 65 nm? Palma D'Antonio
Il 15/03/2011 16:37, David Necas (Yeti) ha scritto: > On Tue, Mar 15, 2011 at 03:52:39PM +0100, Palma D'Antonio - Unifg wrote: >> I'm sorry, I think we are talking of different things. > Probably. > >> I mean that >> using the 'roughness tool' (ISO button) we select a cut-off value in >> order to filter our data (digitalized using a DFT function as you >> previously reported). This cut-off frequency value should be the inverse >> of a parameter measured in meters that we can call 'sampling step' >> (different from tha scan step)., > The profile is a discrete signal sampled with spatial step Δ which is > conceptually different from the scan step but, as I explained, chosen to > be equal. I.e. Δ is the lateral distance between the neighbour points > in the profile (and this happens to be the same as the pixel size). > > The cut-off C is then relative to the spatial frequency 1/(2Δ). I.e. a > cut-off of 1.0 would mean all frequencies (up to the Nyquist frequency > which in DFT sense means simply all because of the mixing of the > low-frequency and high-frequency halves of the spectrum) are included. > > So if I understand correctly your definition of sampling step it is > 2Δ/C. > > Regards, > > Yeti > > > ------------------------------------------------------------------------------ > Colocation vs. Managed Hosting > A question and answer guide to determining the best fit > for your organization - today and in the future. > http://p.sf.net/sfu/internap-sfd2d > _______________________________________________ > Gwyddion-users mailing list > Gwyddion-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/gwyddion-users -- Palma D’Antonio Laboratorio di fisica applicata Dipartimento di scienze biomediche Università degli studi di Foggia Tel e fax 0881 732086 ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Gwyddion-users mailing list Gwyddion-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gwyddion-users
