<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Hello,</div><div><br></div>I know it's not the fastest, but I have found using the ExhaustiveOptimizer at the coarsest resolution can be useful of finding a good starting point. If you are able to get the right resolution (or coarse feature) and the right grid size it should give you a reasonable starting place for iterative methods.<div><br></div><div>Brad</div><div><br></div><div><div>On Sep 16, 2008, at 5:26 AM, Fischer, Sven wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div lang="DE" link="blue" vlink="purple"><div class="Section1"><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">Hi all,<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">I’m doing a 2D 3D registration between fluoroscopic images and CT images, creating a DRR. Since I have several local optima I use a multi resolution approach. I scale the images by a factor of two and do Gaussian blurring. So I scale in 4 steps. First I register the images with one eighth of the original size, than with one fourth, with the half size and finally with the original size. But I have local optima in the first step. So it leads me to misregistration when my starting point is too far away from the final point when my images are correct registered. I can avoid this problem with using a different step size for the Powell optimizer. But when I find a good step size for one starting point it often is useless for other starting points.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">My images are cardiac images, where the aorta and the spine can be seen very clearly. I use the Gradient Difference Metric ( not exactly the ITK-Implementation, I changed it a bit, and it worked very well in several tests ).<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">Do you have an idea how I could find good starting points or how to choose the step size for the Optimizer, depending on the information the image gives me? Or should I use another Optimizer? What is your experience? I’m looking forward to your answers.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">Regards<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span lang="EN-GB" style="font-size: 10pt; font-family: Arial; ">Sven<o:p></o:p></span></font></div></div>_______________________________________________<br>Insight-users mailing list<br><a href="mailto:Insight-users@itk.org" style="color: blue; text-decoration: underline; ">Insight-users@itk.org</a><br><a href="http://www.itk.org/mailman/listinfo/insight-users" style="color: blue; text-decoration: underline; ">http://www.itk.org/mailman/listinfo/insight-users</a><br></div></span></blockquote></div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font face="Helvetica" size="3" style="font: 12.0px Helvetica">========================================================</font></p><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font face="Helvetica" size="3" style="font: 12.0px Helvetica">Bradley Lowekamp<span class="Apple-converted-space"> </span><span class="Apple-converted-space"> </span></font></p><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font class="Apple-style-span" face="Arial"><span class="Apple-style-span" style="font-family: Arial; "><span class="Apple-style-span" style="font-family: Arial; ">Lockheed Martin </span></span></font><font face="Helvetica" size="3" style="font: 12.0px Helvetica">Contractor for</font></p><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font face="Helvetica" size="3" style="font: 12.0px Helvetica">Office of High Performance Computing and Communications</font></p><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font face="Helvetica" size="3" style="font: 12.0px Helvetica">National Library of Medicine<span class="Apple-converted-space"> </span></font></p><p style="margin: 0.0px 0.0px 0.0px 0.0px"><font face="Helvetica" size="3" style="font: 12.0px Helvetica"><a href="mailto:blowekamp@mail.nih.gov">blowekamp@mail.nih.gov</a></font></p><br class="Apple-interchange-newline"></span></div></span> </div><br></body></html>