Re: downsampling methods

Posted by Aviva Vaknin on Nov 16, 2009; 8:57am
URL: http://imagej.273.s1.nabble.com/downsampling-methods-tp3690444p3690452.html

Thanks, Stephan.


I actually started with Gaussian resampling but it blurred the image after
just iterations.
I will read the sites you gave me, perhaps i missed something.

aviva


On Mon, Nov 16, 2009 at 10:46 AM, Stephan Saalfeld <[hidden email]>wrote:

> 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
>