[Insight-users] applying the transformation matrix

[Miller, James V (Research)]

The matrix computed maps from the fixed image's coordinate space to the moving image's coordinate space. As such, if you take a position in the fixed image and apply the transformation, you will have the corresponding position in the moving image.
 
It sounds like you are attempting to do the opposite, which requires either the inverse transform or swapping the fixed and moving images.
 
Jim

	-----Original Message----- 
	From: insight-users-bounces+millerjv=crd.ge.com at itk.org on behalf of Romain Lebel 
	Sent: Tue 12/14/2004 6:22 AM 
	To: insight-users at itk.org 
	Cc: 
	Subject: [Insight-users] applying the transformation matrix
	
	

	Hi every one!
	
	I'm using the itk affine transform to get my images registred.
	The thing is that i need to use the matrix outputed by itk (for
	interfacing with another part of a software).
	
	If i undderstood well the matrix outputed is the one that put the moving
	image in the physical space of the fixed image (no need to use the
	invers transform).
	
	When i apply directly this matrix to the moving image i do not recover
	exactly the registred image ouputed by itk. What i do is take a point in
	the moving image. Compute it's coordinate in the fixed image using the
	matrix. And then get the gray level of the corresponding nearest
	neighboor in the moving image ( i tried linear interpolation and get
	same results so i don't think it is a problem of interpolation)
	
	I tried with wery simple synthesis images (white pad on black
	background). If there is only a translation beetween the image  i manage
	to recover the right image. When there is only scaling i find the right
	scaled image but my center is at the wrong place (no on the center of
	mass outputed by itk)
	
	my question is how to apply the transformation matrix to get the same
	image as the one outputed by itk using resample filter?
	
	ps: sorry for this long mail but i tried to describe as pricisely as
	possible
	
	--
	Romain Lebel
	PhaseView - Telecom Paris
	37-39 rue Dareau, 75014 Paris
	Tel : +33 (0)1 45 81 81 68     Fax: +33 (0)1 45 81 81 44
	Internet :  www.phaseview.fr
	
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