[Insight-users] Scaling in Registration

[Luis Ibanez]

Hi Michael,

Thanks for providing the details of your images.

Note that as a general rule, the only reason for requiring a
'scaling' factor in a registration transform is when the pixels
spacing of one or both of the images is *incorrect*.

In any case, if after reading the chapter on geometrical
transformation, and following the registration tutorial
you still think that you need a scaling factor, the you
can use the Similarity transform or the Affine transform.

Note that these transforms are *VERY* sensitive to the
choice of the parameter scaling passed to the optimizer.

Do not confuse parameter scaling, with the geometric scaling
that you are looking for. The distintion between these two
should be clear for you now that you have read the Chapter
on Registration from the ITK Software Guide.


   Please let us know if you have further questions.


      Thanks


         Luis



-------------------------
Michael Hardisty wrote:

> Hello Luis and others,
> 
> Thanks for your quick and helpful response.
> 
> Answer: 1) When I say smaller, I mean physically (measured in 
> millimeters) smaller.  The image happens to also have less pixels 
> because the region I am concerned with is physically smaller and the 
> pixel spacing remains the same because of the uCT detector.  The reason 
> that I mentioned pixel densities is that if I manually scaled my images 
> to align them the pixel spacings of the two images would differ and 
> hence would have different pixel spacings.  I previously used the word 
> densities as a synonym for spacing I apologize for the confusion.
> 
> I am currently working with a downsampled version of the images that I 
> will eventually have to deformably register.  I am also working with 
> Images that I have artificially deformed to make a set of images that I 
> believe will be similar to the ones I will eventually obtain.  Please 
> note that I am most interested in the mapping between the two images and 
> am less interested in what the images actually look like.  I am looking 
> at the images simply to verify the mapping.
> 
> 
> Test Case Images(downsampled):
> 
> Moving Image:                                         Target Image:
>                                XxYxZ                                   
>                  XxYxZ
> Pixel Number(#):      50x50x50                 Pixel Number(#):      
> 55x55x55
> Pixel Spacing(mm):   0.19x0.19x0.19        Pixel Spacing(mm):   
> 0.19x0.19x0.19
> Origin(mm):              17,10,14                   Origin(mm):         
>     16.6,9.7,13.6
> 
> Real Images(not downsampled):
> 
> Moving Image:                                         Targest Image:
>                                XxYxZ                                   
>                  XxYxZ
> Pixel Number(#):      260x280x280                 Pixel Number(#):      
> 286x310x310
> Pixel Spacing(mm):   0.035x0.035x0.035        Pixel Spacing(mm):   
> 0.035x0.035x0.035
> Origin(mm):              17,10,14                   Origin(mm):         
>     16.5,9.5,13.5
> 
> Thanks for your help with this matter.
>