Hi, Yes, that's correct, we simulate one ray per pixel. Simon On Sat, Feb 20, 2016 at 2:50 PM, Chao Wu <[email protected]> wrote:
> Hi Guangming, > > In many image file format the pixel size (spacing) can be stored within > the file data. If the pixel size in the projection files are correct (e.g. > spacing=1 in your 256x256 P1, or spacing=2 in your 128x128 P2), then you > can use them without giving the newspacing flag. The newspacing flag just > gives you a chance to force RTK to use the pixel size you specified instead > of the one that stored in the image files. > > I am not into rtkSART but I guess the forward projection works with the > input grid, so 128x128 if the input projections are 128x128. Please correct > me if I am wrong. > > Regards, > Chao > > 2016-02-20 14:28 GMT+01:00 Guangming Zang <[email protected]>: > >> Hi Chao, >> Thanks very much for your kind help. i see, now i know there is no >> upsampling at all. >> But i am still a little confused about "then you do not even need to use >> the newspacing flag" . Since if i want to use same geometry(sid, sdd, >> fixed detector size) after dowmsampling (from P1 to P2). >> The size of each projection image changes from 256^2 to 128^2. so to >> maintain the same detector size, the spacing must be 2, i.e, the newspacing >> should set to 2. Is that correct??? >> Actually, the question i have now is that , if before the downsample, >> each image size is 256^2. and in forward projecting part in SART alglrothm, >> say the number of ray generated is 256^2. >> Then after downsampling,i.e., when using P2 as input for rtkSART, what is >> the number of ray generated in forward projections part?? is it 128^2 since >> the number of pixel is 128^2 ??? >> Thanks very much! >> Regards Guangming >> >> On Sat, Feb 20, 2016 at 4:17 PM, Chao Wu <[email protected]> wrote: >> >>> Hi Guangming, >>> >>> There is no upsampling at all. It simply overwrites the pixel size of >>> the projection images stored in the image files. If for instance when you >>> downsampled your P1 to P2 with a factor 2, you also changed the pixel size >>> from 1 to 2 already, then you do not even need to use the newspacing flag. >>> >>> Regards, >>> Chao >>> >>> >>> 2016-02-19 23:50 GMT+01:00 Guangming Zang <[email protected]>: >>> >>>> Hi Simon, >>>> Thanks for your kind reply and information provided. >>>> Basically the problem i encountered is that without changing any >>>> geometry (i.e., sid, sdd, detector physical size), if i downsample my >>>> original projection images, how can i reconstruct corresponding volume >>>> correctly. >>>> In RTK, it seems that i just need to change the input projection file >>>> and newspacing parameter (as same as the factor of downsample), then i got >>>> promising results. but in my own application, i simulate the situation, but >>>> got some aliasing. So i really want to know how it work behind our RTK. >>>> I thought that this parameter is to simulate the detector's spacing >>>> size. >>>> And in my experiment, i set the detector physical size as 256mm*256mm, >>>> and i got projection images P1.mha with size of 256^2 , now i downsample >>>> these images with factor of 2( i.e., the images size change from 256^2 to >>>> 128^2 ), from which i got P2.mha >>>> in our rtkfdk, after the dowmsample. i just need change input >>>> projections from P1.mha to P2.mha, besides, i need change flag newspacing >>>> from 1 to 2. both of the results from RTK are pretty good. >>>> my questions are: >>>> 1) can i just regard the newspacing as the upsample operation with >>>> nearest neighbor filter?? >>>> 2) how many rays RTK generated in forward projecion (i.e. ray tracing >>>> part ) for each image in P2.mha??? is it 256^2???? >>>> >>>> To sum up,in my own application, can i reproduce the result from RTK >>>> for flag "newspacing as 2" by doing: >>>> upsample image by factor of 2 (got a 256mm*256mm image ) and just >>>> generate half number of rays in raytracing (forward priject ) part??? >>>> >>>> Thanks for your time and help in advance, >>>> -Regards Guangming >>>> >>>> >>>> >>>> On Sat, Feb 20, 2016 at 1:15 AM, Simon Rit < >>>> [email protected]> wrote: >>>> >>>>> Hi Guangming, >>>>> The parameter is processed in rtkGgoFunctions >>>>> <https://github.com/SimonRit/RTK/blob/master/code/rtkGgoFunctions.h>.h. >>>>> It's passed to an itk::ChangeInformationFilter >>>>> <http://www.itk.org/Doxygen/html/classitk_1_1ChangeInformationImageFilter.html> >>>>> at the beginning of the rtk::ProjectionsReader.h >>>>> <http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionsReader.html>. >>>>> But in the end, there is nothing to explain, it's simply changes the >>>>> spacing of the input projections. >>>>> I hope this helps, >>>>> Simon >>>>> >>>>> On Fri, Feb 19, 2016 at 8:52 PM, Guangming Zang < >>>>> [email protected]> wrote: >>>>> >>>>>> >>>>>> ---------- Forwarded message ---------- >>>>>> From: Guangming Zang <[email protected]> >>>>>> Date: Fri, Feb 19, 2016 at 10:49 PM >>>>>> Subject: About the newspacing flag >>>>>> To: [email protected], Chao Wu <[email protected]>, >>>>>> Simon Rit <[email protected]>, " >>>>>> [email protected]" <[email protected]>, >>>>>> [email protected] >>>>>> >>>>>> >>>>>> Dear RTK community, >>>>>> i have a question about the parameter "newspacing " in rtkFDK and >>>>>> rtkSART algorithm. >>>>>> it says:--newspacing new spacing of input projections (before >>>>>> pre-processing). >>>>>> I checked in the code, and it seems not easy to find the correct >>>>>> part in the code about the newspacing . >>>>>> So could anyone help me and explain about this parameter?? i want to >>>>>> simulate this preprocess step in my own project and compare to our RTK. >>>>>> -best regards Guangming >>>>>> >>>>>> -- >>>>>> *Guangming Zang (Alex)* >>>>>> *King Abdullah University of Science and Technology(KAUST)* >>>>>> *University of Chinese Academy of Sciences(UCAS)* >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> *Guangming Zang (Alex)* >>>>>> *King Abdullah University of Science and Technology(KAUST)* >>>>>> *University of Chinese Academy of Sciences(UCAS)* >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> ------------------------------ >>>>>> This message and its contents, including attachments are intended >>>>>> solely for the original recipient. If you are not the intended recipient >>>>>> or >>>>>> have received this message in error, please notify me immediately and >>>>>> delete this message from your computer system. Any unauthorized use or >>>>>> distribution is prohibited. Please consider the environment before >>>>>> printing >>>>>> this email. >>>>>> >>>>>> _______________________________________________ >>>>>> Rtk-users mailing list >>>>>> [email protected] >>>>>> http://public.kitware.com/mailman/listinfo/rtk-users >>>>>> >>>>>> >>>>> >>>> >>>> >>>> -- >>>> *Guangming Zang (Alex)* >>>> *King Abdullah University of Science and Technology(KAUST)* >>>> *University of Chinese Academy of Sciences(UCAS)* >>>> >>>> >>>> >>>> >>>> ------------------------------ >>>> This message and its contents, including attachments are intended >>>> solely for the original recipient. If you are not the intended recipient or >>>> have received this message in error, please notify me immediately and >>>> delete this message from your computer system. Any unauthorized use or >>>> distribution is prohibited. Please consider the environment before printing >>>> this email. >>>> >>>> _______________________________________________ >>>> Rtk-users mailing list >>>> [email protected] >>>> http://public.kitware.com/mailman/listinfo/rtk-users >>>> >>>> >>> >> >> >> -- >> *Guangming Zang (Alex)* >> *King Abdullah University of Science and Technology(KAUST)* >> *University of Chinese Academy of Sciences(UCAS)* >> >> >> >> >> ------------------------------ >> This message and its contents, including attachments are intended solely >> for the original recipient. If you are not the intended recipient or have >> received this message in error, please notify me immediately and delete >> this message from your computer system. Any unauthorized use or >> distribution is prohibited. Please consider the environment before printing >> this email. >> > >
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