Setting the gaussian blur

Posted by Mathieu Goeminne on Apr 04, 2008; 11:40am
URL: http://imagej.273.s1.nabble.com/Visualize-orthogonal-views-3D-reconstruction-tp3696642p3696646.html

Hi all,

I try to use ImageJ to blur an image using the API (not the GUI) with a
3x3 convolution matrix gaussian blur. So I use a GaussianBlur object,
and call the blur(ImagePlus, double) method. Comparing the result with
that is obtained using the ImageJ GUI or the GIMP, it appears my call
make an "excessive" blur : for a given sigma (the standard deviation),
"my" blurring is stronger that the Gimp or the ImageJ GUI blurring.

An other problem seems to be an artificial minimum on the sigma : for
every sigma < 1, the result seems to be
Approximately the same as  a sigma=1 blurring. For instance, a sigma=0
blurring blurs really my image, but it should return a non-modified image.

The documentation (and the API) of ImageJ says :

> 'Radius' means the radius of decay to exp(-0.5) ~ 61%, i.e. the
standard deviation sigma of the Gaussian (this is the same as in
Photoshop, but different from the previous ImageJ function 'Gaussian
Blur', where a value 2.5 times as much has to be entered)

I tried to divide my sigma by 2.5, but there is no visible difference,
and the sigma=0 case is not resolved.

I use ImageJ 1.38

Any idea?

Thanks.