[Insight-users] Metric, optimizer choice

[asertyuio]

Hi ITK Users !

After I solved some problems, I managed to do a "successful" 
registration on my images, thanks ITK !
Now I want to raise the question of choosing a metric and an optimizer 
more adapted to my particular data.
I confess I'm a bit lost in all the metrics and optimizer choice.

To clearly explain my problem :
I'm trying to align butterfly wings, that have been already segmented. 
The segmentation process separates the different colour patches into the 
wing and labels them. So I have a different colour number for each wing 
with the RGB value for each too (it is common to have for example one 
shade of orange for one wing, and both a light and dark orange for another).
For the moment, I'm dealing with this by keeping only the intensity 
value on a gray level image and I'm performing on it the registration 
with 2D similarity transform (that I need to do), the MeanSquares 
metrics and the regular step gradient optimizer and a mask to consider 
wing only on metric calculation.
But now, I'm looking for a metric and optimizer that can take advantage 
of my segmentation process, and thus could be faster (I'm around 80 
steps for about 30s)

There are two major problems with my images to take advantage of the 
segmentation :

- The first one is that in different wings, the same label doesn't mean 
same colour, and on the same wing 2 different labels may correspond to 
relatively close colours. Therefore, I can't use the cardinal metric.

- The second one is related to the wing themselves. I must register 
wings that can vary a lot in colour, with for example a patch that can 
be black on some wings and yellow on others. To address this, I was 
thinking using mutual information metric, despite the fact that wings 
have the same modality.


Scale factor is varying between 0.8 to 1.2, rotation between -30° to 
+30°, and translation less than 50 px, my images are round 300*200 px.

Does it make sense to use mutual information on segmented images ?
Does anyone know a couple of metrics optimizers that would correspond 
better to my images ?
Is there any way of limiting optimizer to avoid obvious misregistration 
( like one wing at 90° compare to another ) that happen sometime ?

Thanks a lot for your insights !

Yann