I love that you can just run testing like that with only a couple lines. That's really cool.
Unfortunately, I don't know the answer to your question but Paul might. I'm cc'ing him on this and hopefully he'll see it and be able to answer. Nick On Dec 19, 2012, at 9:22 AM, Bradley Lowekamp <[email protected]> wrote: > Hello Nick, > > Thanks for getting back to me on this. > > I also ran the Sinc interpolators on a constant image, and I got a larger > error than expected. The following Python code was run with the ZeroFlux > boundary condition and the radius template parameter of 5: > > # Create a image of all ones > img = sitk.Image( 10, 10 , sitk.sitkFloat64 ) > img += 1 > > iterps = [sitk.sitkNearestNeighbor, > sitk.sitkLinear, > sitk.sitkBSpline, > sitk.sitkGaussian, > sitk.sitkHammingWindowedSinc, > sitk.sitkCosineWindowedSinc, > sitk.sitkWelchWindowedSinc, > sitk.sitkLanczosWindowedSinc, > sitk.sitkBlackmanWindowedSinc] > > for i in iterps: > eimg= sitk.Expand( img, [10,10], i ) > print "RMS:",(sum( (1-eimg)**2)/len(eimg))**.5, "Abs:", > max(sitk.Abs(1-eimg)) > > RMS: 0.0 Abs: 0.0 > RMS: 0.0 Abs: 0.0 > RMS: 1.90178968104e-16 Abs: 5.55111512313e-16 > RMS: 0.0 Abs: 0.0 > RMS: 0.00519432546396 Abs: 0.007170554427 > RMS: 0.00111584107245 Abs: 0.00190357704047 > RMS: 0.000697067283848 Abs: 0.00118879124085 > RMS: 0.00143647177089 Abs: 0.00245097611656 > RMS: 0.000491351024756 Abs: 0.000833429218405 > > Skimming through the code it looks like the kernel is point sampled and not > integrated over the pixel. I wonder if that is the issue. > > Brad > > On Dec 18, 2012, at 3:03 PM, Nicholas Tustison <[email protected]> wrote: > >> Hi Brad, >> >> Yeah, we just use the default. We've probably never noticed it since, >> as you say, we typically are interpolating a blob in the middle of a black >> background. >> >> I think Paul Yushkevich wrote those windowed sinc interpolators. You >> might want to ask him why they're the default. >> >> Nick >> >> >> >> On Dec 18, 2012, at 1:09 PM, Bradley Lowekamp <[email protected]> wrote: >> >>> Hello, >>> >>> As I am finally integrating the different interpolators into SimpleITK. I >>> am giving them a close look over. >>> >>> The set of WindowSincInterpolateImageFunctions takes a Boundary condition >>> template parameter. This defaults to ConstantBoundaryCondition. That is by >>> default the pixels are zero outside the image, and they are not zero flux. >>> This results in quite a bit of ringing and fading around my test images. It >>> seems just wrong. >>> >>> I can easily specify this parameter as the ZeroFluxNeumannBoundaryCondition >>> (I don't think we have a mirror/reflective boundary, which is another >>> possibility), and things look quite good and as I expect the output to be. >>> I was curious as to what others were doing so I perused BRAINS and ANTS, >>> grepping for the sinc interpolator. And to my surprise they are using the >>> default! >>> >>> Is there a reason that this default is preferred? Or is it that I am not >>> processing a single blob in the center of a black image (aka a brain)? >>> >>> Also in terms of consistency across the interpolators, this is the only one >>> which takes a boundary condition template parameters. The other >>> interpolators appear to behave sensibly, and exhibit a zero-flux type >>> boundary condition. I think the default for this may need to be changed. >>> >>> >>> I have this little example I have been working on in SimpleITK with the >>> famed cthead1.png data input. Here is a code snippet: >>> >>> >>> image = >>> image[(size[0]//2-25):(size[0]//2+25),(size[1]//2-25):(size[1]//2+25)] >>> >>> >>> iterps = [sitk.sitkNearestNeighbor, >>> sitk.sitkLinear, >>> sitk.sitkBSpline, >>> sitk.sitkGaussian, >>> sitk.sitkHammingWindowedSinc, >>> sitk.sitkCosineWindowedSinc, >>> sitk.sitkWelchWindowedSinc, >>> sitk.sitkLanczosWindowedSinc, >>> sitk.sitkBlackmanWindowedSinc] >>> >>> eFactor=5 >>> >>> image_list = [] >>> >>> for i in iterps: >>> image_list.append( sitk.Expand( image, [eFactor]*3, i )) >>> >>> tiles = sitk.Tile( image_list, [3,0] ) >>> >>> And the following is the output with the different boundary conditions: >>> >>> http://erie.nlm.nih.gov/~blowek1/images/expand_interp_cbc.png >>> http://erie.nlm.nih.gov/~blowek1/images/expand_interp_zfbc.png >>> >>> Thanks for you feedback, >>> Brad >> > _______________________________________________ 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
