[Insight-users] A Few Questions and Problems

[Luis Ibanez]

Hi Amitesh



1) The recommended limit for a stable time step to be used with the
    anisotropic diffusion filters is presented in the Doxygen
    documentation of these filters.

http://www.itk.org/Insight/Doxygen/html/classitk_1_1AnisotropicDiffusionFunction.html

> Typical
> values are less than 0.250. A stable value for most 2 and 3d
> functions is 0.125. In general, you should keep the time step below
> 1/2^N, where N is the number of image dimensions. A filter will
> automatically attempt to constrain its time step to a stable value
> and generate a run-time warning if the time step is set too high.



2) I assume that you mean what are the values needed in the Sigmoid
    filter when you use it as a pre-processor for the speed image
    to be used in LevelSets.

    If so, you will find a detailed explanation on this topic in the
    ITK Software Guide

            http://www.itk.org/ItkSoftwareGuide.pdf

    Section 9.3.1, pdf-page 369.




3) Removal of the blue gel from the cryogenic data of the
    Visible Woman dataset is fairly straightforward.


    Just use the source code available in:


       InsightDocuments/
                SoftwareGuide/
                           Cover/
                              Source/
                                  VWBlueRemoval.cxx


http://www.itk.org/cgi-bin/viewcvs.cgi/SoftwareGuide/Cover/Source/VWBlueRemoval.cxx?rev=1.1&root=InsightDocuments&view=log




4) Lino Ramirez kindly contributed to ITK last week his
    implementatino of Closing and Opening:

    http://www.itk.org/pipermail/insight-users/2004-December/011591.html

    we will commit those new filters to the CVS repository
    very soon.



   Regards,



       Luis


--------------------------
Amitesh Agarwal wrote:

> Hello,
> 
> I have been using ITK for last few months and hence come across a few
> problems. I would really appreciate any help at all in this matter. At
> present I am working on Image extraction from a grayscale 3D image in
> .vtk file format.
> 
> 1) Gradient Anisotropic Diffusion Image Filter
>          I had initially used suggested values, as given in ITK 1.4
> Software Guide (6.5), for number of iterations, timestep and
> conductance parameter. However at runtime the filter gave a warning
> that the timestep (0.125) chosen for this 3D image is unstable one and
> the minimum stable timestep is (0.0625). I accordingly did the same. 
> It is my understanding that the filter has come from the solution of
> heat diffusion equation and timestep delta t in the CFL condition
> determines stability or unstability of a particular implementation of
> a computational scheme. My question is that In that situation How can
> I find a stable timestep for a particular image for Image processing
> purpose?
> 
> 2) Sigmoid Image Filter
> 
> Is there any method by which I can find the optimum value alpha and
> beta for a 3D image so that I can obtain best result. Will that be
> possible in ITK? Is there any similar implementation anywhere in the
> form of piece/chunk of code?
> 
> 3) Removal of Cryogenic Gel
> 
> At present I am stuck in the problem of removal of Cryogenic gel from
> the dataset. I am not sure how it can be done in ITK but to me it
> seems that the best possible way it could be done would be using flood
> fill with zero intensity pixels in the gel area with a single seed
> point (if it could somehow be done in ITK!!). Some details about
> removing the cryo gel has been mentioned In the ITK book (About the
> cover Page) but it is not very clear to me. Can anybody help me with
> that?
> 
> 4) Opening and closing operation in a binary image
> 
> I just wanted to know if there is any filter present in ITK for
> performing opening and closing operation in a given Binary Image. It
> is my understanding that BinaryErode and BinaryDilate do similar
> operation in effect but not exactly the same.
> 
> Regards
> 
> Amitesh
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