[Rtk-users] Fwd: About the newspacing flag

Sat Feb 20 08:58:53 EST 2016

Hi Chao and Simon,
Thanks so much for the kind help. Now i got it after you guys  detailed
explanation.
Have a good weekend!
-Best regards Guangming

On Sat, Feb 20, 2016 at 4:53 PM, Simon Rit <simon.rit at creatis.insa-lyon.fr>
wrote:

> Hi,
> Yes, that's correct, we simulate one ray per pixel.
> Simon
>
> On Sat, Feb 20, 2016 at 2:50 PM, Chao Wu <wuchao04 at gmail.com> 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 <guangming.zang at kaust.edu.sa>:
>>
>>> 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 <wuchao04 at gmail.com> 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 <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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>>>>>>>
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>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> *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
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>>>>>
>>>>
>>>
>>>
>>> --
>>> *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
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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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