[Insight-users] Demons registration stopping criteria

[Luke Bloy]

I'm curious about the stopping criteria used in the demons based 
registrations.

 From looking at itkFiniteDifferenceImageFilter::Halt() it seems that 
the stopping criteria are one of either 2 things.
    1) the number of iterations exceeds some maximum.
    2) the RMS_change is less then some MaximumRMSError.

In the demons algorithm the RMS_change is defined as the average of the 
length of the update displacement field. Which seems to never decrease 
significantly.

Am I correct that there is no stopping criteria based on the image 
similarity metric? If not what would be the most sensible way/place to 
add such a criteria? Is there any interest in having this functionality?

thanks,
Luke