[Insight-users] itkCenteredRigid2DTransform registration optimization problems

[Rupert Brooks]

Hi Felix:

>
> My registration results are either perfect or misaligned, the correct
> solution definitely has the best metric value.
>
> Yes I also thought that a grid-search on the lowest scale might be an
> option, rising the question, how dense this grid should be.
>

A difficult question - one way to explore it is to probe the value of
your cost function around the minimum and look for how wide the dip
is, then divide up your space so that you are sure to fall into the
right dip.  However, since you seem to have two fairly good dips in
your registration space, This might be difficult - it might be
difficult to tell one good dip from another.  I lean towards the next
option.

> Trying flippings on pyramid top might do, on the other hand, I would
> like to keep cost down as much as possible, because I have to register
> several tens-thousands of images in total (serial sectioning stacks).

This is the way i would probably go - and it might be the cheapest and
easiest to implement.  You could put it in an observer that is called
when the registration changes levels.  On the first change of levels,
the observer could rotate the object 180, evaluate the metric and, if
that is better set the next level registration parameters to the
rotated transform and carry on.

Whatever you do, I'd be very curious to know how it works out.
>
> In my MATLAB prototype I use an initial principal-axis-transform for
> bulk initialization, but I found the itkImageMomentsCalculator not so
> well documented. Have you used it?

Unfortunately no, not beyond running the example in the ITK book.  I'm
sure that someone out there has though :-)

Best,
Rupert
-- 
--------------------------------------------------------------
Rupert Brooks
McGill Centre for Intelligent Machines (www.cim.mcgill.ca)
Ph.D Student, Electrical and Computer Engineering
http://www.cyberus.ca/~rbrooks