[Insight-users] ”Hello World” Registration from the ItkSoftwareGuide?

[Luis Ibanez]

Hi Motes,

Your new images are not appropriate input data for
an image registration test.

         They contain almost no information.

The local derivatives of the metric will be zero almost
every where in the parametric space.

The cost function of the problem that you have devised
looks almost like a Diract delta.  It has constant values
every where, an a very high value in a single point.

No gradient-based optimizer would figure out in what
direction to walk to get to the peak of the cost function.

The only stochastic optimizer may have a chance to
solve the problem that you have set, and still they could
only solve it by accidentally hitting that singular point in
which the cost function has a non trivial value.

You should use images whose spatial distribution of
pixel intensities can give you a local gradient on the
Cost Function (image metric).



     Regards


            Luis


---------------------------------------
On Sun, Jun 21, 2009 at 3:20 PM, motes motes <mort.motes at gmail.com> wrote:

> I am playing around with the example from the ItkSoftwareGuide.pdf page
> 316. When using the brain images I get rather good results:
>
> http://img37.imageshack.us/img37/4316/example1z.jpg
>
> showing in the order: fixed, moving, resampled, rescaled intensity.
>
> I have then tried making my own very simple fixed and moving image to
> compare:
>
> http://img23.imageshack.us/img23/4744/example2t.jpg
>
> Here the result are not that well (the same order as above). For some
> reason the box is only translated very little towards the position in the
> fixed image. Any ideas why it does not align better with this simple
> example? The resulting translation transform does not transform very
> correct.
>
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