[Insight-users] Necessary overlapping when computing metric in registration

[Karthik Krishnan]

Depends on the metric. Please look at the code of the metric in question.

For MeanSq its at least 1 sample, as you suspect.
  Line 110: itkMeanSquaresImageToImageMetric.txx
     if( !this->m_NumberOfPixelsCounted )

itkMattesMutualnformationImageToImageMetric imposes a 25% overlap threshold.
  Line 1109 :   if( nSamples < m_NumberOfSpatialSamples / 4 )

Your threshold overlap is metric dependent. Overall a low overlap -> low
confidence in metric.

For MI, overlap is quite important, since with MI can increase as overlap
reduces, making the optimizer unstable, and driving the registration towards
the 0 overlap point.



-- 
Karthik Krishnan
R&D Engineer,
Kitware Inc.

On Fri, Jul 31, 2009 at 7:42 AM, Gomez Herrero, Alberto <
alberto.gomez-herrero at philips.com> wrote:

>  Hi,
>
>
>
> In the frame of a registration process, I am exploring a metric to get the
> values for each displacement, something similar to what is done in the
> example MeanSquaresImageMetric1.cxx.
>
> My question is the following:
>
>
>
> To compute the metric for a given displacement, the two images have to
> overlap at least partially. What is the minimum overlap? One may think that
> any overlap > 0 should work, but my tests make my think that actually at
> least one full pixel of the moving image must be fully overlapping the fixed
> image, otherwise throws exception. Can anyone confirm this please?
>
>
>
> Thanks,
>
>
>
> Alberto
>
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