[Insight-users] sigmoidImageFilter

[Luis Ibanez]

Hi Jihan,

In the Speed image the Zero values represent borders
of the object to be segmented, and the One values
represent the inside of the object.

Please note that the Speed image is NOT the segmentation,
it is only the map of where the LevelSet will be allowed
to grow.

The inside of the LevelSet will be the segmentation.

Strictly speaking, what you need is the speed image to
be non-zero inside of the object, and to have "close to"
zero values in the borders, so that the LevelSet propagation
will be stopped there.

The values outside of the object could be set to any other
value...

In practice, what tend to happen is that the border of the
object is not exactly zero in the speed image, and therefore
the Levelset manage to go through the border and "leak"
to the outside of the object.

All this will be clearer if you study the images in the
ITK Software Guide,  in the LevelSet section.


     Regards,


             Luis


----------------------------
On Wed, Jul 1, 2009 at 7:11 PM, Jihan Zoghbi <jihanzoghbi at gmail.com> wrote:

> Hi Luiz,
>
> Thank you for the answer. The values of 1.0 and 0.0 represent  the object
> to be segmented or  the whole image, where we have Zeros in the borders and
> 1 inside the borders of the objects in the image?
> best regards.
>
>
> 2009/7/1 Luis Ibanez <luis.ibanez at kitware.com>
>
>
>> Hi Jihan,
>>
>> This is done because we are computing a Speed image.
>>
>> The ideal speed image have Zero values in the borders
>> of the object that you are segmenting, and have 1.0
>> values inside the object, in order to facilitate the rapid
>> propagation of the LevelSet.
>>
>>
>>       Regards,
>>
>>
>>            Luis
>>
>>
>> -------------------------------------------------------------------------
>> On Wed, Jul 1, 2009 at 4:06 PM, Jihan Zoghbi <jihanzoghbi at gmail.com>wrote:
>>
>>>
>>> Hi everybody,
>>>
>>> Anyone knows why in the  file GeodesicActiveContourImageFilter.cxx the
>>> values of the MIn and Max values are 0.0 and 1.0 respectively as follows?
>>> sigmoid->SetOutputMinimum(  0.0  );
>>> sigmoid->SetOutputMaximum(  1.0  );
>>> -
>>> Thanks
>>> Jihan Zoghbi
>>>
>>>
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>>
>
>
> --
> Jihan Zoghbi
>
>
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