[vtkusers] reasons of limitations on opacity per component and up to 4 components in label-map volume rendering?

[Sankhesh Jhaveri]

Hi,

In short, VTK’s support for label map masks is limited.

I’m not sure what you mean by opacity. If you see the documentation for
vtkGPUVolumeRayCastMapper::SetMaskInput
<https://www.vtk.org/doc/nightly/html/classvtkGPUVolumeRayCastMapper.html#a57d26b71335b8d904cf1adde6ba976b6>,
it explains how the final sample color is determined.

As to why it works the way it does, I’ll defer to the authors but more
likely, this was all that was required from the mapper at the time it was
written.

The mapper might actually work(I’ve not tested this, but should, in
general) with N number of components given that
vtkProperty::IndependentComponents is set. The limitation of a maximum of 4
components is when they are treated as dependent.

Hope this helps.

Thanks,
Sankhesh
​

On Sun, Jun 10, 2018 at 9:10 PM terminator via vtkusers <
vtkusers at public.kitware.com> wrote:

> Hi everyone,
> Although subject is clear enough, but I want to know what's the reasons of
> these limitations?
> I found out that vtk supports up to 4 components in label map volume
> rendering (with mask). I can set colors for each component, but just first
> opacity (index=0) will applied and others will be ignored. Is there
> technical issue for controlling each component opacity separately?
> My last question, why number of components is restricted to four? seems the
> overhead of a few transfer functions is not too much.
>
>
>
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-- 
Sankhesh Jhaveri *Sr. Research & Development Engineer* | Kitware
<http://www.kitware.com/> | (518) 881-4417
​
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