This is certainly going to require more thought. But if you shrink by 3, and your image is divisible by 3 does that appear to introduce a bias aswell?
I have a fiter which does average a "shrink" region which can be easily used in an external module[1]. Perhaps that would be more appropriate for your current application. This issue has been debated about before. I'd be curious as to what you think of this [2] abandoned gerrit topic. Brad [1] https://github.com/blowekamp/itkBinShrink [2] http://review.source.kitware.com/#/c/8179/ On Jul 18, 2013, at 10:54 AM, sgerber <[email protected]> wrote: > Hi Brad > > Thank you for your feedback and taking the time to look at the images. I am > fairly certain that the "bias" is introduced due to the subsampling strategy > used in the ShrinkImageFilter, if an average would be used the bias would > disappear. > > -Sam > > > On 2013-07-17 11:51, Bradley Lowekamp wrote: >> Hello Sam, >> >> I looked at the images you provided here: >> >> http://www.cs.utah.edu/~sgerber/tmp/pyramids.zip [3] >> >> in Slicer3D. I would agree that test1 from the RecursivePyramid with >> the shrink filter does not appear to align up correct. So you are >> likely onto something. >> >> What I have found useful for many of these types of geometric filters >> is to create an image of points of the physical location of center of >> the pixels, or a set of images if the filter in question doesn't >> support the multi-component pixels. Then pass this through the filter. >> Aside from potential boundary conditions the the pixel values of the >> output should still be the physical location of the pixel in the >> output. This can create useful and definitive tests. >> >> Brad >> >> On Jul 17, 2013, at 11:15 AM, sgerber <[email protected]> wrote: >> >>> Hi >>> >>> RecursiveMultiResolutionPyramidImageFilter behaves significantly different >>> when using UseShrinkImageFilterOff() vs. UseShrinkImageFilterOn(). The >>> default, UseShrinkImageFilterOn(), uses for subsampling a single pixel >>> ("top right" corner) which results, for piecewise constant images, in image >>> gradients being shifted in physical space. Is this intended? It's not the >>> behaviour I expected when I used this filter. It is also not documented in >>> the PyramidFilter documentation or the ShrinkImageFilter that this is the >>> subsampling method used. >>> >>> Thanks >>> Sam >>> _______________________________________________ >>> Powered by www.kitware.com [1] >>> >>> Visit other Kitware open-source projects at >>> http://www.kitware.com/opensource/opensource.html [2] >>> >>> Kitware offers ITK Training Courses, for more information visit: >>> http://kitware.com/products/protraining.php >>> >>> Please keep messages on-topic and check the ITK FAQ at: >>> http://www.itk.org/Wiki/ITK_FAQ >>> >>> Follow this link to subscribe/unsubscribe: >>> http://www.itk.org/mailman/listinfo/insight-developers >> >> >> >> Links: >> ------ >> [1] http://www.kitware.com >> [2] http://www.kitware.com/opensource/opensource.html >> [3] http://www.cs.utah.edu/~sgerber/tmp/pyramids.zip _______________________________________________ Powered by www.kitware.com Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Kitware offers ITK Training Courses, for more information visit: http://kitware.com/products/protraining.php Please keep messages on-topic and check the ITK FAQ at: http://www.itk.org/Wiki/ITK_FAQ Follow this link to subscribe/unsubscribe: http://www.itk.org/mailman/listinfo/insight-developers
