[Insight-users] optimizer scales

[Michael Kuhn]

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