[Rtk-users] Fwd: About the newspacing flag

[Chao Wu]

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 <guangming.zang at kaust.edu.sa>:

> 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 <simon.rit at creatis.insa-lyon.fr
> > 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 <
>> guangming.zang at kaust.edu.sa> wrote:
>>
>>>
>>> ---------- Forwarded message ----------
>>> From: Guangming Zang <guangming.zang at kaust.edu.sa>
>>> Date: Fri, Feb 19, 2016 at 10:49 PM
>>> Subject: About the newspacing flag
>>> To: rtk-users-request at public.kitware.com, Chao Wu <wuchao04 at gmail.com>,
>>> Simon Rit <simon.rit at creatis.insa-lyon.fr>, "
>>> rtk-users at public.kitware.com" <rtk-users at public.kitware.com>,
>>> rtk-users at openrtk.org
>>>
>>>
>>> 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)*
>>>
>>>
>>>
>>>
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>>
>
>
> --
> *Guangming Zang (Alex)*
> *King Abdullah University of Science and Technology(KAUST)*
> *University of Chinese Academy of Sciences(UCAS)*
>
>
>
>
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