Yes, there is no such limitation as far as I know, you can use negative numbers and value above 1. Your result is really strange, it it supposed to be a square? I don't know what is the problem but that's clearly a geometry issue. We can always have a look if you're able to share some data. Simon
On Wed, Jun 3, 2020 at 1:56 PM Andreas Andersen <andreasg...@gmail.com> wrote: > I don't think there are any restrictions technically. > You should be able to use negative values, as the main arithmetic is just > a sum > <https://github.com/SimonRit/RTK/blob/master/include/rtkBackProjectionImageFilter.hxx#L106> > and a multiplication > <https://github.com/SimonRit/RTK/blob/master/include/rtkBackProjectionImageFilter.hxx#L115> > . > > The only restriction I can see is that this sum and multiplication should > not overflow (or underflow for negative values) the underlying type of the > output image, as that would be undefined behaviour. Over- and underflow is > unlikely for float, unless you have extremely high values (see wikipedia > for floating point range > <https://en.wikipedia.org/wiki/Floating-point_arithmetic#Range_of_floating-point_numbers> > ). > > /Andreas > > __________________________________ > > Andreas Gravgaard Andersen > > Danish Center for Particle Therapy, > > Aarhus University Hospital > > Palle Juul-Jensens Blvd. 99, > > 8200, Aarhus > > Mail: agravga...@protonmail.com > > Cell: +45 3165 8140 > > > On Wed, 3 Jun 2020 at 03:34, Benjamin W. Maloney < > benjamin.w.maloney...@dartmouth.edu> wrote: > >> Hi, >> >> I thought the same in regards to trying to rotating in the other >> direction. Unfortunately, that has a similar artifact but with the >> reconstruction flipped. >> Interestingly the overlap happens in a similar place but the internal >> structures are flipped >> >> 1. Thanks! >> 2. I should have worded that better. My projection images will be >> preprocessed in a float format. I wanted to check if there were >> restrictions on these float values. Can input image data have negative >> values or high values? Or are they expected to have values between 0 and 1? >> I ask because some of the tools I have used to do this preprocessing >> (outside of RTK) have given negative values or 'stretched' the data from 0 >> to 255 before saving. >> >> Ben >> >> ------------------------------ >> *From:* Simon Rit <simon....@creatis.insa-lyon.fr> >> *Sent:* Tuesday, June 2, 2020 5:28 PM >> *To:* Benjamin W. Maloney <benjamin.w.maloney...@dartmouth.edu> >> *Cc:* rtk-users@public.kitware.com <rtk-users@public.kitware.com> >> *Subject:* Re: [Rtk-users] Reconstruction Artifact >> >> Hi, >> Sometimes rotating in the wrong direction gives this kind of artefacts. >> It's quite possible that we don't use the same convention as other toolkits >> regarding this. >> For other questions: >> 1. Yes, you can use pixel as the unit. Then the image spacing should be 1 >> obviously and indeed, sdd and sid should be in pixels. >> 2. I don't fully understand. If your data is the output of a count >> detector, then you either rely on RTK to guess the counts without object to >> compute the line integral, or your preprocess your projections to pass line >> integrals in a float format. >> Simon >> >> On Tue, Jun 2, 2020 at 4:51 PM Benjamin W. Maloney < >> benjamin.w.maloney...@dartmouth.edu> wrote: >> >> Hi all, >> >> Not sure if this is the right group to post to but here's my question: >> >> I have a code that pulls in my own projection images and uses >> the FDKConeBeamReconstructionFilter for reconstruction >> >> The reconstruction I am getting has an artifact where it looks like there >> are two overlapping objects rotated. >> I have used other reconstruction toolboxes (mainly TIGRE in MATLAB) with >> the similar geometry inputs and not had this issue. I suspect the >> difference is in the parts of the geometry that are set by default. My >> question is if anyone has seen this before and what input I should look >> into? >> >> I have a few more questions I may or may not be related: >> 1. I assume that since I set the origin etc of my images in pixel, sid >> and sdd should be in pixels as well? >> 2. Are there restrictions related the scalar values of the projection >> data? My data will be in detector counts rather than linear attenuation >> coefficients, is that okay? >> I have attached an image to show this issue. It is supposed to be a >> rectangular mammography phantom. It is a slice in XZ plane >> >> Thanks for the help! >> Ben >> >> >> >> _______________________________________________ >> Rtk-users mailing list >> Rtk-users@public.kitware.com >> https://public.kitware.com/mailman/listinfo/rtk-users >> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpublic.kitware.com%2Fmailman%2Flistinfo%2Frtk-users&data=02%7C01%7CBenjamin.W.Maloney.TH%40dartmouth.edu%7Cf356eebd76e348edabd908d8073ba140%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637267300000289534&sdata=72i1zusf0mqK%2BTPPzqJ%2FEcLg62KFiReV%2FyaB3jlUSU0%3D&reserved=0> >> >> _______________________________________________ >> Rtk-users mailing list >> Rtk-users@public.kitware.com >> https://public.kitware.com/mailman/listinfo/rtk-users >> >
_______________________________________________ Rtk-users mailing list Rtk-users@public.kitware.com https://public.kitware.com/mailman/listinfo/rtk-users
