[vtkusers] change contrast in volume object (it's too dark)

[Mark Wyszomierski]

Hi Lisa,
 First I had my MIP function using SetMaximizeMethodToScalarValue(), and it 
looks like setting the opacity transfer function had no effect. If I switch 
to SetMaximizeMethodToOpacity(), then the transfer function does have an 
effect, though it is a strange effect. The areas of my organ dataset that 
have the greatest intensity will appear as bright white both in the 2D 
slices, and in the MIP rendering if maximize scalars is on (areas like 
veins/artieries etc). Now that I set maximize to use opacity, and adjusted 
the ramp, yes I can have only those really bright areas stand out, but since 
their opacity is high I guess they are really dark grey now! It almost looks 
like an inverted MIP. Should I specify a color mapping now too? My input is 
one component unisigned short.
 The window and leveling for the image viewer classes is very interactive 
with good response times. If I were to try the same thing binding the 
opacity ramp to be interactive for this volume, I can get a refresh maybe 
once every 1 - 2 seconds per change. That's why I am still wondering about 
hooking into the output of the rendered volume somehow, so window / level 
would only be done on the output image instead of every voxel in the volume, 
then resampling etc, does this sound feasible/possible?
 I posted the relevant lines for my MIP below in case I'm doing something 
wrong:
 OpacityTransferFunction->AddPoint(0, 0);
OpacityTransferFunction->AddPoint(0, 300.0);

Volume->SetProperty(VolumeProperty);
CompositeFunctionMIP->SetMaximizeMethodToOpacity();
VolumeMapper->SetVolumeRayCastFunction(CompositeFunctionMIP);
VolumeMapper->SetInput((*this->pImageData));
Volume->SetMapper(VolumeMapper);

Thank you!

On 9/2/05, Lisa Avila <lisa.avila at kitware.com> wrote: 
> 
> Hello,
> 
> You would apply the window / leve directly to the opacity transfer 
> function
> - just adjust the start / end points of the ramp. If it is too dark, lower
> the point at which the opacity becomes 1.
> 
> Lisa
> 
> At 09:03 AM 9/2/2005, powerhouseofexcellence wrote:
> >Hi all,
> >
> >I have the VTK users guide book (version 4.4) and was reading to see how
> >to edit the diffuse/ambient etc to make my volumes look brighter (problem
> >from an earlier post). But I'm doing a MIP, and the book says that these
> >parameters and the ShadingOn() are ignored by MIP rendering. So my MIP
> >still looks dark, any way to increase their brightness? I am using the
> >scalar value as the maximize function.
> >
> >I was hoping that since the volume data is being passed to the render
> >window somewhere, maybe there would be a chance to set the output of the
> >volume renderer into a window level filter which is then passed along to
> >the render window. So only the final output is window/leveled and this
> >could be a quick operation. Is this possible?
> >
> >Thanks
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