[Insight-users] anisotropic diffusion or Discrete gaussian

[Xavier Mellado Esteban]

    Hello,

    You should take a look at ITK User's Guide, if you haven't done it yet:

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

    "Section 6.7 Smoothing Filters" discusses a bit the gaussian and  
the anisotric filters.

    Extracted from the user's guide:

> The drawback of image denoising (smoothing) is that it tends to blur  
> away the sharp boundaries
> in the image that help to distinguish between the larger-scale  
> anatomical structures that one
> is trying to characterize (which also limits the size of the  
> smoothing kernels in most applications).
> Even in cases where smoothing does not obliterate boundaries, it  
> tends to distort the fine
> structure of the image and thereby changes subtle aspects of the  
> anatomical shapes in question.


    I have used them a bit and the main difference is what they say.  
Theorically, the gaussian filter will help to denoise and to have  
smooth derivatives, but it will blur the borders of "small" structures  
on your image. On the contrary, the anisotropic will tend to preserve  
the borders, but I do not know if it has any bad influence on the  
derivatives.

    In any case, the use of one filter or the other will depend a lot  
on the kind of image and which are the structures you want to study.  
Besides, the parameters used in each filter will change substantially  
the results, so you have to tune them for your particular case.

    My understanding is, if your image is not really noisy and you  
want to help the derivatives, you could smooth it a bit with the  
gaussian (check first that your gradient filter do not smooth it  
again). If your image is noisy, try to denoise it with the  
anisotropic, and then apply the gaussian as I told before. My advice  
is, try to avoid the gaussian as a denoise filter unless your  
structures are really big.

    Wait for other users, probably they can give you better answers. I  
hope this helps you.

                     Regards,
                                Xavi




Leila Baghdadi <baghdadi at phenogenomics.ca> ha escrito:

> Hi guys
>
> does anyone know the difference between the above two and the pros and
> cons of using each for before creating the image gradient for
> segmentation
>
>
> thanks
>
> Leila
>
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