[Insight-users] Can a metric be negative in ITK?

[Christopher Kappe]

Hello everybody, 

I'm new to this list. 
I'm trying to do registration with two 3D images. I basically used the 
ImageRegistration8.cxx example (using itk 4.0 btw) but with 
MattesMutualInformationMetric instead of MeanSquaresMetric. 
And, well, I got output like this from the observer: 

0   -0.00130253  
1   -0.000181399 
2   -0.00019049   
3   -5.82618e-06
4   -6.76423e-06 
5   -1.81517e-05  
6   -1.78196e-05   
7   -7.79246e-06  
8   -4.0121e-06
9   -3.87818e-06 
10   -1.20782e-05   
11   -2.655e-06   
12   -1.13154e-05  
13   -7.53967e-06  
14   -8.0584e-06  
15   -3.52788e-06 
16   -2.35729e-06
17   -5.10754e-06
18   -6.61478e-05
19   -0.000101335
...
49   -0.000806308 
Optimizer stop condition: VersorRigid3DTransformOptimizer: Maximum number of 
iterations (50) exceeded.
          Probe Tag    Starts    Stops             Time (s)
        Registration           1            1           4509.42

The thing is, it's not even converging (at least not towards 0).
And is it okay to get a negative metric as result in the first place?

Best
Paul Muetze