[Insight-users] Optimizer does not converge in CenteredSimilarity2DTransformation

[Jan Biel]

Hello!

I am using the following elements to register two images 
recorded with different modalites one of which is subject 
to a rotation, scaling and translation:

* MutualInformationImageToImageMetric
* NormalizeImageFilter
* GradientDescentOptimizer
* CenteredSimilarity2DTransform
* CenteredTransformInitializer
* LinearInterpolateImageFunction
* DiscreteGaussianImageFilter

Unfortunately, the optimizer does not seem to converge and 
the results are rather bad. In fact, starting from a 
decent configuration the optimizer chooses to pick worse 
values despite specifying the MaximizeOn parameter.

Can anyone tell me what might be the problem? What further 
information would be necessary to track down the problem?

I have provided a plot of the metric values here:

http://www.janbiel.de/im/plot.gif

Additionally I get the following results, which seem more 
than odd to me:

Result =
  Scale         = -8.62898
  Angle (radians) -1.16491
  Angle (degrees) -66.7447
  Center X      = 112.206
  Center Y      = 128.331
  Translation X = 0.122154
  Translation Y = 0.479044
  Iterations    = 200
  Metric value  = 0.00104807

That with an initial metric value of 0.0757717.

Thanks in advance,
Janbiel