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<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">Hi Folks,<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">I really like the changes implemented for ITK v4 registration. The composite transform makes multistage registration much easier to implement. Nice work!<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"> <o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">Is there a way to explicitly set the fixed and moving images to be used at each level of a multiresolution registration? How about the gradient images used by the image metric? I see
you can set gradient filters on the metric, but what if you already have the gradients precomputed?<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"> <o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">I get the feeling that v4 registration runs slower than similar v3 registration, but I think it’s mainly down to the initialization where the fixed and moving images are smoothed and
the metric computes the image gradients.<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"> <o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">It seems like there could be some real advantages to using precomputed smoothed and gradient images. For example, the smoothing could be implemented with a cascade of Gaussians where
the standard deviation used at a level k is given by s^2 = s_k^2 - s_{k-1}^2. Or the smoothing could be implemented on the GPU. Or we could be reusing a resolution level in a different registration stage, perhaps optimizing a different set of transform parameters.<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"> <o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">Have I missed something in the API where it is possible to explicitly set the images and gradients to use at each level of the registration? I could probably create an itk::Command that
swaps the fixed and moving images before each registration iteration, but is there a way to disable the smoothing step?<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">Regards,<o:p></o:p></span></p>
<p style="margin:0in;margin-bottom:.0001pt"><span style="font-size:14.0pt">Brian<o:p></o:p></span></p>
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