[Rtk-users] Lateral blur in a FDK reconstructed volume

[Vincent Libertiaux]

On 25.04.22 09:07, Simon Rit wrote:
> Hi Vincent (and Jasper),
> I agree with Jasper that this is most likely due to a difference in 
> geometric calibration between the two datasets. Do you have more 
> information on what does B use (projection matrices, detailed 
> parametrization, etc.)? I think that such a blur can be caused by a 
> difference in source to detector distance (or, equivalently, detector 
> pixel size).
> Simon
>
> On Tue, Apr 19, 2022 at 11:08 AM Vincent Libertiaux <vl at xris.eu> wrote:
>
>     On 16.04.22 13:52, Jasper Albertus Nijkamp wrote:
>     > Hi Vincent,
>     >
>     >  From just these two images, it is a bit hard to help. However,
>     I have seen similar challenges when the detector vertical offset
>     is not properly set. If you could share a bit more data (fx
>     projection data and the geometry), more people might be able to help.
>     >
>     > Jasper
>     >
>     > -----Original Message-----
>     > From: Rtk-users <rtk-users-bounces at public.kitware.com> On Behalf
>     Of Vincent Libertiaux
>     > Sent: Friday, 15 April 2022 17:15
>     > To: rtk-users <rtk-users at public.kitware.com>
>     > Cc: Damien Koch <dk at xris.eu>
>     > Subject: [Rtk-users] Lateral blur in a FDK reconstructed volume
>     >
>     > Hello rtk users !
>     >
>     > I am facing a problem for which I have exhausted all the
>     possibilities except asking you.
>     > I have performed a standard FDK reconstruction of a lego bricks
>     assembly.  I used a custom-made code to compute the detector
>     horizontal offset and tilt angle, found to be 1.15 mm and 0.02°
>     respectively.  The result of the reconstruction is shown in the
>     picture
>     > https://ibb.co/LdMzJF2 . The volume looks mostly sharp, except
>     on the lateral edges, let's say on the last half brick.
>     >
>     > We had the opportunity to have the same volume reconstructed
>     with two commercial solutions.  The first one, "A", produced the
>     same results than rtk.  The second, "B", produced the result shown
>     in the picture https://ibb.co/VwXMmRH
>     >
>     > In this case, the edges are sharp too.  The offset values found
>     with this software were very close (1.13mm and 0.025°
>     respectively) and feeding them to rtksimulatedgeometry didn't
>     change my result.  No other correction was allegedly applied.
>     >
>     > I thought that the edge blurring was due to a wobbling artefact
>     but it can't be the case according to the result with the "B"
>     software.
>     >
>     > Do you have any idea on what could cause this blurring on the
>     edges ?
>     >
>     > I thank you very much for any clue.
>     >
>     > Best regards,
>     >
>     > Vincent
>     >
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>
>     Hi Jasper,
>
>     thank you for your reply. I had already tried to play with the
>     vertical
>     offset but setting it to a value different than 0 progressively
>     decrease
>     the overall quality of the reconstruction.
>     Following your advice, here are the projections:
>
>     http://share.xris.eu/d91b09673bba
>
>     word of warning, the set is very large (900 projections on a
>     3072x3072
>     pixels detector, approx. size = 16Go)  I could try and make it
>     smaller
>     by downsampling it but I am afraid it would mask the problem. I
>     can try
>     and do it on request.
>     The geometric parameters I used were: SDD = 810 mm, SID = 410 mm,
>     proj_iso_x = 1.15mm and in_angle = 0.02°.
>
>
>     Best regards,
>
>     Vincent
>
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Hi Simon,

thank you for your reply.  I unfortunately don't have information on 
what B uses. I just know for sure that the geometric parameters were 
rigorously the same than the one I used with rtk.  I'll keep 
investigating and let you know if I get another info (or find the 
answer, a man can dream...:) )

Best regards,

Vincent
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