[Insight-users] noise and normalized correlation

[Luis Ibanez]

Hi Romain,

The Normalized correlation metric is not partiularly sensitive
to noise in the Fixed and Moving image.

 From just the description of the components that you used it
is difficult to tell what may be the cause of the problem.

Most of the times you are dealing with the need for fine-tuning
the parameters of your application.

In general you want to first solve the registration problem by
using a Rigid transform, and then use that solution for initializing
an Affine transform.

In your partiuclar case, since you seem to be interested in Shearing
but not in scaling, then you should probably consider the use of the
Transform

http://www.itk.org/Insight/Doxygen/html/classitk_1_1ScaleSkewVersor3DTransform.html


You should also connect Observers to your optimizer, as illustrated
in the ITK Software Guide


             http://www.itk.org/ItkSoftwareGuide.pdf


and plot the progression of the registration paramters.

This will help you to identify the source of the problem.


You will also fond useful to generate an exploratory plot
of your image metric around the 'optimal' value, so you
can get familiar with the characteristics of the cost
function (the image metric). In that way, you will be
able to stablish whether the image noise significantly
affects the cost function.



    Regards,


        Luis


------------------
Romain Lebel wrote:
> Hello everyone!
> I'm currently testing the normalized correlation metric on my 
> registration problem
> I need to register an image on another knowing that the moving image 
> translates, and that there is a small scale on the image. The moving 
> image is captured at a different height so it is defocused (implies a 
> bluring)
> I'm using the affin transform with the optimizerscaleparameter[1] and 
> [2] to a great value so that no rotation is possible (i used to set them 
> to 1 and i had a big shearing effect does anyone faced this?)
> I'm using the RegularStepGradientDescentOptimizer and linear interpolator.
> I tried it on very simple synthesis images and it works fine. But when i 
> add noise on them the translation is ok but the scaling is wrong (even 
> when i filter the images using a median filter)
> Is this metric very sensitiv to noise or does it come from the optimizer?
> Or maybe the cause is ohterwhere....?
>