[Insight-users] [Insight-developers] two-input filters don't work

[Kevin H. Hobbs]

Michael, sorry for the "dupe" due to the list's file size limit I'm
resending this. The images I mention are at :

http://crab-lab.zool.ohiou.edu/kevin/two-input_filters

On Thu, 2009-09-17 at 18:10 +0200, Michael Xanadu wrote:
> In step 9 of your mail you said to put the output of sigmoid to the
> input of fastMarching. That made me stunning, because in the examples
> of two-input-filters (i.g. itk manual page 542) fastMarching never has
> an input. Is it a failure or did you do so on purpose?

I said that on purpose.

The examples use fast marching only as a very rough initialization for
the other filters. It produces only a circle of about the right radius
centered on the object to be segmented.

The fast marching filter can either advance through the image at a
constant speed, essentially labeling every pixel with its distance from
the seed point, or it can advance with a speed equal to the value of an
input image at each point.

This behavior is controlled by :

giving the filter no input image, setting the size of the output image,
and setting a speed constant

OR

giving the filter an input image.

From your image "4 fast Marching.PNG" I can see that constant speed was
used. Don't use it. 

Also don't set the output size.

It's not that there is anything wrong with using constant speed for fast
marching, it's just that you clearly do not have your feature image
quite right yet and we need to get that fixed before we can move on. 

Now from looking at your image "3 sigmoid.PNG" it looks like you could
get regions like those I've highlighted with the GIMP from the fast
marching filter ( some of these will likely merge if the input is 3D )
is that what you want?


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