[Insight-users] 3D rigid registration

[Karthik Krishnan]

Grace Chen wrote:

>Hi Karthik,
>
>By centering the image, I mean to make coordinate (0,0,0) to the center of
>the image.
>
>  
>
Why are you doing this ?

>If I do that on one of the input images, then I need to shift the other
>image by the same amount in the same direction (by reseting the origin).
>  
>
It is always a bad idea to shift the origin of your image. The right 
thing to do is to compute a transform that will overlay the images 
according to your needs and leave the origins of the images intact.

>Don't we need to center the images for the center transform to work well?
>  
>
No. The CenteredTransformInitializer does that for you as detailed in 
the earlier email. " It computes the transform, which when applied to 
the moving image would align the two images via their geometric centers. 
It is one way of starting the registration from an initial transform.".

Please refer to the examples first.

-karthik

>Grace
>
>----- Original Message ----- 
>From: "Karthik Krishnan" <Karthik.Krishnan at kitware.com>
>To: "Grace Chen" <Grace.Chen at swri.ca>
>Cc: <insight-users at itk.org>
>Sent: Monday, June 05, 2006 5:14 PM
>Subject: Re: [Insight-users] 3D rigid registration
>
>
>  
>
>>Grace Chen wrote:
>>
>>    
>>
>>>Hi,
>>>
>>>If I center just one image and shift another image....
>>>
>>>      
>>>
>>What do you imply when you say :
>>"If I center just one image and shift another image" ?
>>
>>  A minimal example might help
>>
>>    
>>
>>>The result is quite
>>>different (slice shift 2 slices forward) from if I don't center any input
>>>images....
>>>
>>>Can some ITK people please tell me if I should center input images at
>>>      
>>>
>all??
>  
>
>>>      
>>>
>>If you have datasets of the same anotomical region, acquired in the same
>>manner, it is sometimes useful them via their geometrical centers:
>>
>>    
>>
>http://www.itk.org/Insight/Doxygen/html/classitk_1_1CenteredTransformInitializer.html
>  
>
>>You will need to look at the datasets to see if aligning them via their
>>geometrical centers makes sense. There is no hard and fast rule here.
>>
>>There are several examples that you can refer to on using this class:
>>
>>./Registration/ImageRegistration12.cxx
>>./Registration/ImageRegistration13.cxx
>>./Registration/ImageRegistration14.cxx
>>./Registration/ImageRegistration6o.cxx
>>./Registration/ImageRegistration7o.cxx
>>./Registration/ImageRegistration6.cxx
>>./Registration/ImageRegistration7.cxx
>>./Registration/ImageRegistration8.cxx
>>./Registration/ImageRegistration9.cxx
>>
>>    
>>
>>>      
>>>
>>>>Hi there,
>>>>
>>>>To use VersorRigid3DTransform for 3D rigid registration, should we
>>>>        
>>>>
>center
>  
>
>>>>both of the input imgaes?  It seems wrong to center both images.....If
>>>>        
>>>>
>we
>  
>
>>>>need to center just one image, which one, the fixed image or the moving
>>>>image??
>>>>
>>>>
>>>>        
>>>>
>>To clarify:  When you "center images", you are computing the transform,
>>which when applied to the moving image would align the two images via
>>their geometric centers. It is one way of starting the registration from
>>an initial transform.  I suppose, you have a different notion of "center
>>images prior to registration".
>>
>>    
>>
>>>>Please help!  This part of using ITK can't seem to be found anywhere....
>>>>Thanx!
>>>>
>>>>Grace
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>_______________________________________________
>>>Insight-users mailing list
>>>Insight-users at itk.org
>>>http://www.itk.org/mailman/listinfo/insight-users
>>>
>>>
>>>
>>>      
>>>
>
>
>  
>