<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Hello,</div>
<div>in the file rtkSARTConeBeamReconstructionFilter.h there is briefly written how the</div>
<div>forward and back projection is performed. For the forward projection, every pixel is</div>
<div>divided by the intersection length of the ray with the volume. That is clear to me.</div>
<div> </div>
<div>For the back projection applies the following text:</div>
<div>"each voxel of the back projection must be divided by the value it would take if<br/>
a projection filled with ones was being reprojected. This weighting step is not<br/>
performed when using a voxel-based back projection, as the weights are all equal to one<br/>
in this case. When using a ray-based backprojector, typically Joseph,it must be performed."</div>
<div> </div>
<div>That means a temporary projection image is created where all pixels have the value "1". So far I understand,</div>
<div>if we use a voxel based back projector we do not need to apply this weighting step because the ray from source to voxel center</div>
<div>somewhere hits the detector plane and usually there we interpolate the pixel value. But all of them are "1" so it's obsolete to</div>
<div>interpolate inbetween.</div>
<div> </div>
<div>But if we use for instance the joseph back projector don't we calculate the four weightings at the current volume planes the</div>
<div>ray intersects with ? So we already have weightings that range from 0 to 1. I'm a little bit confused about the projection image</div>
<div>filled with "1". So how a this back projection of "1" actually happens ?</div>
<div> </div>
<div>I hope someone can help me with that. Thank you.</div>
<div> </div>
<div>best regards,</div>
<div>Robert</div>
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