Gaussian filter

[Jarek Korzan]

How to get a 1.Gaussian filter (kernel size= 30x30)
and Gausian filter (Sigma =35 pixels, kernel size=33x 33)
JKorzan

[Michael Schmid]

Hi Jarek,

sorry, I don't fully understand your question.

If you truncate a Gaussian filter with sigma=35 pxl down to
kernel size 33x33 it won't have much similarities with a
Gaussian filter any more, it will almost be a uniform kernel
(similar result as ImageJ Process>Filter>Mean).

ImageJ's Gaussian Blur command currently uses a kernel radius
of 2.5 sigma, so a Gaussian filter with sigma=35 pxl will
seem to have a 176x176 kernel. Actually, it uses two
convolutions, one by a 176x1 and one by a 1x176 kernel.

ImageJ 1.38r, expected for next week or so, will have a smoother
kernel (truncating a Gaussian at 2.5 sigma still leads to a
noticable step), corresponding to roughly sigma=3.5 to 4.

So, in the current version of ImageJ, if you want a certain
value of the standard deviation sigma, you have to enter 2.5
times that value as a radius. With ImageJ 1.38r, you have to
enter the standard deviation directly, and ImageJ will calculate
an appropriate kernel size.

Michael
_______________________________________________________________

On Fri, 4 May 2007 21:33:57 +0200 Jarek Korzan <[hidden email]> wrote:
>How to get a 1.Gaussian filter (kernel size= 30x30)
>and Gausian filter (Sigma =35 pixels, kernel size=33x 33)
>JKorzan
>

[Robert Dougherty]

Jarek,

You might want to look at the 2D Gaussian filter plugin on the ImageJ
plugins page.  There is also a 3D version at
http://www.optinav.com/download/Gaussian_PSF_3D.java. ImageJ's built in
approach, mentioned by Michael, should be faster for blurring in
large-radius cases like you describe.

Bob

Robert P. Dougherty, Ph.D.
President, OptiNav, Inc.
Phone [phone]
Fax [phone]
www.optinav.com
 

[Michael Schmid]

Hi Jarek, Bob,

if your problem is speed, you may try the latest build of ij.jar.
It uses a faster algorithm, especially for large sigma.

http://rsb.info.nih.gov/ij/ij.jar

In case of problems with the faster Gaussian Blur, let me know,
please.

Michael
___________________________________________________________________

On Sat, 5 May 2007 07:35:51 -0700 Robert Dougherty <[hidden email]>
wrote:

>Jarek,
>
>You might want to look at the 2D Gaussian filter plugin on the ImageJ
>plugins page.  There is also a 3D version at
>http://www.optinav.com/download/Gaussian_PSF_3D.java. ImageJ's built in
>approach, mentioned by Michael, should be faster for blurring in
>large-radius cases like you describe.
>
>Bob
>
>Robert P. Dougherty, Ph.D.
>President, OptiNav, Inc.
>Phone [phone]
>Fax [phone]
>www.optinav.com
>

... [show rest of quote]