[vtkusers] How does VTK OSPRay-based volume rendering produce smooth images?

[Alexander Devaykin]

Hello everyone,

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).

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).

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).

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.

Screenshots or standalone OSPRay and ParaView-OSPRay renderings are
attachend.

Best Regards,
Alexander Devaykin
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