<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: times new roman,new york,times,serif; font-size: 12pt; color: #000000'>Yes, I checked now, indeed one of the images has a lot of empty background, so, it kind of makes sense, but I will still verify everything with respect to the center of the image as you mentioned. <div>Finally now I can go ahead and write my codes, I was really stuck</div><div>. </div><div>Thanks</div><div>Vikash<br><br><hr id="zwchr"><blockquote style="border-left:2px solid rgb(16, 16, 255);margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Torsten Rohlfing" <torsten@synapse.sri.com><br><b>To: </b>"Vikash Gupta" <vikash.gupta@inria.fr><br><b>Cc: </b>"Vikash Gupta" <write2vikash@gmail.com>, insight-users@itk.org<br><b>Sent: </b>Friday, September 14, 2012 12:33:46 AM<br><b>Subject: </b>Re: [Insight-users] Image Registration<br><br>
<br>
<div class="moz-cite-prefix">On 09/13/2012 03:27 PM, Vikash Gupta
wrote:<br>
</div>
<blockquote cite="mid:1999793107.15404749.1347575255901.JavaMail.root@inria.fr">
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<div style="font-family: times new roman,new york,times,serif;
font-size: 12pt; color: #000000">Hi Torsten,
<div>Thanks once again for your patient email. Yes so I
resampled the moving image to the fixed image space, with the
output transformation matrix (my output transformation matrix
is inverted) and I get the image in the expected co-ordinates
of the fixed image.</div>
<div>So, I will apply this transformation (or the inverse) to
the points in physical spaces of the images in order to take
one to other or the way around, as you suggested. </div>
<div><br>
</div>
<div>One last thing that startles me as i mention before is the
gap between the translation parameters, which intutively
should be more, but I didn't write the registration routine so
probably that is an issue I should find out by looking at the
registration routine, how things are implemented there. </div>
</div>
</blockquote>
<br>
Well, one explanation for the near-zero translation despite very
different origins could be if the images had very different fields
of view.<br>
<br>
If you simply add a lot of background around one of the images
without changing the physical coordinates of the pixels that are
already there, then you will need to adjust the image origin
accordingly, but the translation vector would not change at all.<br>
<br>
The point here is, that the first pixel in your image (which is the
origin pixel) rarely has any meaningful anatomy information, so
where it maps matters little to nothing. It is usually more
interesting to see where the CENTER pixel maps; I suspect in your
images, the center of each is near the zero physical coordinate. So
if you have your object of interest (e.g., patient) centered in your
images, and the center is also the zero coordinate, then there would
be little translation needed to align them. Yet, if the images have
different fields of view, your origins would be very different.<br>
<br>
And you're very welcome :)<br>
<br>
TR<br>
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