[Insight-users] about registration : Direction of the Transform

[Luis Ibanez]

Hi Sophie,


This is indeed one of the features that tend to confuse ITK users
when they start getting to know the Image Registration Framework.


We actually had to add a section to the ITK Software Guide to
better explain the direction in which the ITK Tranforms are
applied in the context of ImageRegistration.



You will find this discussion in the ITK Software Guide

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

in section 8.3 "Features of the Registration Framework" in
pdf-page 356. (paper page 324).


In particular you should read subsection

       8.3.1. "Direction of the Transform Mapping"

in pdf-pages 359-360. along with the diagram in page 358.


This section explains the direction of the transfrom in
detail. The diagram is particularly important.


Please take a look at this section and let us know if you
still have any questions or comments.


     Regards,


        Luis



---------------
Sophie wrote:
> 
> Dear Luis,
>  
> I have written to a few minutes ago about registration. Now I have 
> another question. In chapter 8 Registration of ItkSoftwareGuide.pdf, the 
> example ImageRegistration1.cxx shows a registration between a fixed 
> image and a moving image which is the result of intentionally 
> translating the fixed image by (13,17)millimeters. The resulting 
> transform parameters are:
> 
> Translation X = 12.9959
> Translation Y = 17.0001
>  
> So I am more confused, why not -12.9959 and -17.0001 because the 
> transform presents how a moving image can be mapped to the fixed one.
>  
> Sophie
>  
> The following is my last letter, they are more or less the same question.
> 
> ---------- Forwarded message ----------
> From: *Sophie* <comet1986 at gmail.com <mailto:comet1986 at gmail.com>>
> Date: 2008-8-24 22:45
> Subject: about registration
> To: Luis Ibanez <luis.ibanez at kitware.com <mailto:luis.ibanez at kitware.com>>
> 
>  
> Dear Luis,
>  
> I am doing registration of an liver image sequence to get the movement 
> of liver in a certain time. However, here comes a problem: Which one 
> should be set as the fixed image?
>  
> In the beginning, I set the first image from the sequence as the fixed 
> image, while the following ones are provided as the moving image one by 
> one. Then I get a continual result of this image sequence. (TX1,TY1; 
> TX2,TY2;.............)
>  
> But when I plot the y-translation, it seems the value of y-translation 
> should be calculted by (-1). Since the transform is used for mapping the 
> moving image to fixed image, I am wondering if I should take the first 
> image as the moving image while the others as the fixed image one by 
> one. I am really confused now :(
>  
> Thank you very much!
>  
> Happy every day ^_^