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

[David E DeMarle]

Most likely the only difference is that VTK sets up OSPRay's volume
sampling differently than the OSPRay demos do.
You will find how it is setup here:

https://gitlab.kitware.com/vtk/vtk/blob/master/Rendering/OSPRay/vtkOSPRayVolumeMapperNode.cxx#L255

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.



David E DeMarle
Kitware, Inc.
Principal Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909

On Mon, Jul 3, 2017 at 5:46 PM, Alexander Devaykin <xaxellx at gmail.com>
wrote:

> 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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