[Insight-users] optimizer scales

[Luis Ibanez]

Hi Michael,

Your assumption is correct,

The scaling factors must be proportional to the
physical extent of the image.

These factors are used by the optimizer in order
to compensate the difference in dynamic range
between the quaternion components and the translation
components.

I want to get rid of this dependency, simply compute
the translation part of the scale as a multiple of the
diagonal of your image measured in millimeters.



Regards,


   Luis


-----------------------------
Michael Kuhn wrote:
> Hi,
> 
> I want to perform a registration between two images A and B for 
> different resolutions. This means, I do a registration between images A1 
> and B1 (which, for example, have a size of 100x100x100 pixels in unit 
> spacing) and between images A2 and B2 (which contain the same image 
> data, but are smaller (for example 70x70x70 pixels, unit spacing as well 
> (i.e. their extent is smaller in pixel as well as in world 
> coordinates)). I'm using a quaternion transform and a quaternion rigid 
> transform gradient descent optimizer.
> 
> Is it correct, that in order to perform the same registration, I have to 
> rescale the 'translation scales' passed to the optimizer? Thus, I think, 
> if I register A1 and B1 and use a scale array of [1, 1, 1, 1, 0.0001, 
> 0.0001, 0.0001] then I have to use a scale array of [1, 1, 1, 1, 
> 0.000143, 0.000143, 0.000143] to register A2 and B2 (where 0.000143 = 
> 0.0001 / 0.7). Is this assumption correct and does it hold for all 
> possible factors (not only for 0.7)?
> 
> Thanks,
> 
> Michael
> 
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