Hi Luis,<br><br>Thanks a lot for your helpful suggestions. For the point (6), what do you mean by saying "t is common to have to construct your segmentation by combining fragments that are extracted at different water levels" ? Do you mean I need some<br>
connectedcomponentImageFilter after watershedImageFilter to combine fragments?<br><br>Thanks again!<br>gator<br><br><div class="gmail_quote">On Sun, Nov 1, 2009 at 4:53 PM, Luis Ibanez <span dir="ltr"><<a href="mailto:luis.ibanez@kitware.com">luis.ibanez@kitware.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi Gator,<br>
<br>
1) Yes, if you are working on a CT Image, it tends to be useful<br>
to do some denoising before running a Watershed filter.<br>
<br>
<br>
2) A rule of thumb is to set the Threshold to be about 1 / 100<br>
of the Level.<br>
<br>
<br>
3) Typical values of level are 0.2 ~ 0.3.<br>
<br>
But of course, they vary with the structure that you want to<br>
extract, and the image that you are providing as input<br>
<br>
<br>
4) Please not that usually you want to run the watershed filter<br>
not in the image directly but in its GradientMagnitude image,<br>
... unless... you are lucky enough to be searching for an<br>
anatomical structure that is dark and it is fully surrounded by<br>
brighter objects.<br>
<br>
<br>
5) Finding a set of parameters that will work for a full set of<br>
images is a challenging problem, and it doesn't have a<br>
trivial answer.<br>
<br>
What we can suggest you are tools for making this easier:<br>
<br>
We have found effective to use<br>
<br>
a) CMake Macros to define tests for each one<br>
of the images in the set, and then run all the<br>
tests by using ctest.<br>
<br>
b) Batchmake (<a href="http://www.batchmake.org" target="_blank">www.batchmake.org</a>).<br>
<br>
<br>
6) Note also, that the watershed filter will rarely provide a<br>
segmentation solution by looking at a single level.<br>
It is common to have to construct your segmentation<br>
by combining fragments that are extracted at different<br>
water levels.<br>
<br>
<br>
<br>
Regards,<br>
<br>
<br>
Luis<br>
<br>
<br>
--------------------------------------------------<br>
<div><div></div><div class="h5">On Fri, Oct 30, 2009 at 12:38 PM, Gator Philly <<a href="mailto:gatoratphilly@gmail.com">gatoratphilly@gmail.com</a>> wrote:<br>
> Hello itk gurus,<br>
><br>
> In order to effectively use watershedImageFilter, how to optimize those two<br>
> parameters: Level and Threshold?<br>
> If I have a multiple set of 3D CT images, each set of 3D CT images might<br>
> have different voxel intensity characteristics,<br>
> it seems from my experiments that one set of parameters for all sets might<br>
> not the optimal solution. How can I<br>
> choose the parameters based on the characteristics of given set?<br>
><br>
> The other question I have is should I do some denoising pre-processing such<br>
> as median filter before I do watershed?<br>
><br>
> Thanks a lot for any suggestions and comments.<br>
> Best,<br>
> Gator<br>
><br>
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