http://imagej.273.s1.nabble.com/downsampling-methods-tp3690444p3690451.html
> On Mon, 2009-11-16 at 11:52 +0100, Gluender wrote:
> > Just a note:
> >
> > Downsampling at least in theory definitely requires a _real_ bandlimit.
> >
> > That said, Gaussian lowpass filtering surely is not optimum because
> > per definition it doesn't really zero frequency components above the
> > Nyquist limit.
> >
>
> This is correct for functions that are created through a spectral
> generator which we assume is the case for an image when transferring it
> to the frequency domain from it's intensity samples but in fact is not.
> For an image captured with a camera it is just better to re-sample by
> diffusion, that is through the focus of a Gaussian.
>
> Best,
> Stephan
>
> > >Hi Aviva,
> > >
> > >you should try Gaussian downsampling:
> > >
> > >In Fiji, there is a Javascript in PLugins->Examples->downsample
> > >explained at
> > >
> > >
http://pacific.mpi-cbg.de/wiki/index.php/Downsample> > >
> > >the same Javascript is at the ImageJ website
> > >
> > >
http://rsb.info.nih.gov/ij/macros/js/Downsample.js> > >
> > >or, alternatively a public API method in the packages of mpicbg_.jar
> > >that are part of Fiji, such that you can call it for a nopen Image, say,
> > >from Plugins->Scripting->BeanshellInterpreter:
> > >
> > >import ij.*;
> > >import mpicbg.ij.util.Filter;
> > >new ImagePlus( "downsampled", Filter.scale(
> IJ.getImage().getProcessor(),
> > >0.2f ) ).show();
> > >
> > >Lanczos being just an approximation of a bandpass filter in the
> > >frequency domain, you could also try to do the downsampling directly
> > >through that bandpass-filter, ImageJ has the respective functions.
> > >Depends very much on what you want. For most cases, the Gaussian thing
> > >is just optimal.
> > >
> > >Best,
> > >Stephan
> > >
> > >
> > >
> > >On Mon, 2009-11-16 at 08:07 +0200, Aviva Vaknin wrote:
> > >> Hello all!
> > >>
> > >> I have implemented a Lanczos8 kernel convolution to downsample images
> > >> which works well for 30-40 iterations.
> > >>
> > >> After that ringing artifacts enter, even if I reduce a 1600x1200
> image one
> > >> pixel
> > >> each iteration.
> > >>
> > >> Should this be occurring ? Is there a way around it ?
> > >> Is there a better down sampling method for this type of problem ?
> > >>
> > >> thanks,
> > >> aviva
> >
> > Best
>