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: [email protected] Cell: +45 3165 8140 On Wed, 3 Jun 2020 at 03:34, Benjamin W. Maloney < [email protected]> 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 <[email protected]> > *Sent:* Tuesday, June 2, 2020 5:28 PM > *To:* Benjamin W. Maloney <[email protected]> > *Cc:* [email protected] <[email protected]> > *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 < > [email protected]> 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 > [email protected] > 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 > [email protected] > https://public.kitware.com/mailman/listinfo/rtk-users >
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