<div dir="ltr"><div><div><div><div>Hello,<br><br></div>sorry for late reply and thank you for the answers!<br></div>I actually managed to achieve nice smooth surface of the volume thanks to your help! And I didn't see any significant performance change at least on the datasets at hand.<br><br></div>Best regards,<br></div>Alexander<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Jul 6, 2017 at 7:52 PM, Brownlee, Carson <span dir="ltr"><<a href="mailto:carson.brownlee@intel.com" target="_blank">carson.brownlee@intel.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">The smoothness of the resulting image is based on several factors, notably: number of accumulation passes, number of samples per pixel, samplingStep, and adaptive sampling settings.
Please see the OSRPay documentation for an explanation of each.<br>
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The volume renderer in VTK appears smoother because the samplingStep and adaptive sampling settings were set for taking more samples than the viewers that come with OSPRay, which were designed speed in mind and rely on progressive rendering to smooth the image
after the first frame. We assumed that with VTK and ParaView that most users would not be using progressive refinement, which unfortunately is likely a mostly unknown feature in ParaView.<br>
Carson<br>
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<div id="m_983496297836877922divRpF398473" style="direction:ltr"><font size="2" color="#000000" face="Tahoma"><b>From:</b> David E DeMarle [<a href="mailto:dave.demarle@kitware.com" target="_blank">dave.demarle@kitware.com</a>]<br>
<b>Sent:</b> Thursday, July 06, 2017 7:15 AM<br>
<b>To:</b> Alexander Devaykin; Brownlee, Carson<br>
<b>Cc:</b> <a href="mailto:vtkusers@vtk.org" target="_blank">vtkusers@vtk.org</a><br>
<b>Subject:</b> Re: [vtkusers] How does VTK OSPRay-based volume rendering produce smooth images?<br>
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<div>Most likely the only difference is that VTK sets up OSPRay's volume sampling differently than the OSPRay demos do.<br>
You will find how it is setup here:<br>
<a href="https://gitlab.kitware.com/vtk/vtk/blob/master/Rendering/OSPRay/vtkOSPRayVolumeMapperNode.cxx#L255" target="_blank">
https://gitlab.kitware.com/<wbr>vtk/vtk/blob/master/Rendering/<wbr>OSPRay/<wbr>vtkOSPRayVolumeMapperNode.cxx#<wbr>L255</a><br>
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Note also: starting with ParaView 5.3, if you start ParaView with --enable-streaming, and set "Progressive Passes" on the Properties panel to something higher than one, ParaView will do progressive refinement like you see in the OSPRay demos.<br>
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<div>David E DeMarle<br>
Kitware, Inc.<br>
Principal Engineer<br>
21 Corporate Drive<br>
Clifton Park, NY 12065-8662<br>
Phone: 518-881-4909</div>
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<div class="gmail_quote">On Mon, Jul 3, 2017 at 5:46 PM, Alexander Devaykin <span dir="ltr">
<<a href="mailto:xaxellx@gmail.com" target="_blank">xaxellx@gmail.com</a>></span> wrote:<br>
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<div>Hello everyone,<br>
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I wonder how does OSPRay-based volume renderer in VTK, used in ParaView, is able to produce volume images with smooth surface from the first pass (without buffer accumulation).<br>
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OSPRay raw volume rendering e.g. using OSPRay demos, results in very densly sampled volumes. It looks like only one sample per voxel is taken which results in one pixel per voxel colored in the first pass at some regions (image 1). Only after several accumulation
passes the rendering produces smooth image (image 3).<br>
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In contrast to that, volume rendering in ParaView via OSPRay shows smooth image after first pass (image 4) with a little bit of densly sampled artifacts. It actually looks like no frames accumulation is active at all, because I no difference is visible between
moving and resting camera. Zooming in also keeps the image smooth (image 5).<br>
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Any articles or hints about what is going on behind the scenes? I'm digging into the VTK source code but no understanding so far. OSPRay seems to be configured just like I do in my application, but VTK seems to do the magic somewhere else.<br>
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<div>Screenshots or standalone OSPRay and ParaView-OSPRay renderings are attachend.<br>
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Best Regards,<br>
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Alexander Devaykin</div>
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