[vtkusers] Transparency of binary segmentation mask (ImageActor2D + LUT)

[Charlotte Curtis]

Hi Jeff, thanks for the reply.

I'm not sure what you mean by exactly the same location - it's true
that they are at the same xy location, but they are on different
layers, or at least that's what I'd like them to be doing.  I tried
changing the Z location with Mapper->SetZSlice, but this just resulted
in the entire segmentation mask becoming opaque (including the values
that are mapped through the LUT to an alpha of zero).

I tried setting the opacity of both images to 0.5 as you suggested
(using actor->GetProperty()->SetOpacity()), and this didn't seem to
change anything.  Even setting the opacity to zero results in opaque
images, although if I set the alpha of my LUT values to zero the image
does indeed disappear.

If I print various values to std::cout, everything seems to be in
order - for example, overlayRenderer->Transparent() returns 1,
overlayActor->GetProperty()->GetOpacity() returns whatever I set it to
(0.5), etc.  I thought perhaps there was something wrong with my
system graphics/opengl setup, but if I build and run the "medical 3"
example I do get a transparent volume.  Reading through the code in
that file, the only difference I could see was that it uses a single
renderer with multiple actors so I tried that as well, but nothing
seemed to change.

Thanks again for the help,

Charlotte

On Tue, Mar 24, 2009 at 8:09 AM, Jeff Baumes <jeff.baumes at kitware.com> wrote:
> It looks like the images are displayed at exactly the same location? I
> believe the image mapper maps a texture to a quad, so perhaps you have
> conflicting geometry. The other thing I would try is to set the
> opacity of both images to less than 1.0 (like 0.9 and 0.5), so that
> they are both rendered in the same render pass. VTK first renders any
> opaque geometry, then renders translucent geometry, so that may be why
> it gets obscured.
>
> Jeff
>
> On Mon, Mar 23, 2009 at 9:38 PM, Charlotte Curtis <c.f.curtis at gmail.com> wrote:
>> Hi all,
>>
>> I've got a couple of images displayed on top of each other, one a 2D
>> medical image, and the other a binary segmentation mask.  They each
>> have their own image actors and renderers, and I created a lookup
>> table for the segmentation mask in the hopes that it would let me
>> render the mask as semi-transparent colours.  Right now I've got two
>> values in the LUT (corresponding to the image values of 0 and 1), and
>> I can change the colours, but the transparency is binary - if I set
>> the alpha value to 0, it doesn't display, but if it's anything else
>> (even 0.001) then the mask is completely opaque.
>>
>> I've also tried changing the opacity of the actor
>> (actor->GetProperty->SetOpacity()), but this doesn't seem to do
>> anything, although when I print out the value of the actor's opacity
>> it thinks that it is set correctly.
>>
>> Perhaps my window/levels are wrong?  I'm kind of at a loss.  Apologies
>> if this has been asked (seems like a common problem, but I couldn't
>> find a solution so far).  Thanks,
>>
>> Charlotte
>>
>> // Create the common components for the image viewer
>> vtkRenderWindow* renWin = vtkRenderWindow::New();
>> vtkRenderWindowInteractor* interactor = renWin->MakeRenderWindowInteractor();
>> interactor->SetRenderWindow( renWin );
>>
>> // Create the components for the image display
>> vtkRenderer* imageRenderer = vtkRenderer::New();
>> vtkActor2D* imageActor = vtkActor2D::New();
>> vtkImageMapper* imageMapper = vtkImageMapper::New();
>>
>> // Set the values and connect them together
>> imageMapper->SetColorWindow( 1024 );
>> imageMapper->SetColorLevel( 512 );
>> imageMapper->SetInput( connector->GetOutput() );
>> imageActor->SetMapper( imageMapper );
>> imageRenderer->AddActor( imageActor );
>>
>> // Create the components for the mask layer
>> vtkRenderer* overlayRenderer = vtkRenderer::New();
>> vtkActor2D* overlayActor = vtkActor2D::New();
>> vtkImageMapper* overlayMapper = vtkImageMapper::New();
>> vtkLookupTable* overlayLUT = vtkLookupTable::New();
>> vtkImageMapToColors* colourMapper = vtkImageMapToColors::New();
>>
>> /************************* This is the part that's not behaving
>> ********************************/
>> // set properties of the various overlay components
>> //overlayActor->GetProperty()->SetOpacity( 0.5 ); this doesn't seem to
>> do anything
>> double outsideColour[4] = {1.0, 0, 0, 0.5};  // This one shows up as
>> completely opaque red.
>> double insideColour[4] = {1.0, 1.0, 1.0, 0}; // This one doesn't show,
>> which is correct.
>> overlayLUT->SetNumberOfTableValues(2);
>> overlayLUT->SetTableRange(0, 1);
>> overlayLUT->SetTableValue( 0, outsideColour );
>> overlayLUT->SetTableValue( 1, insideColour );
>> overlayLUT->Build();
>> overlayMapper->SetColorLevel( 0.5 );
>> overlayMapper->SetColorWindow( 0.5 );
>>
>> // Connect the overlay stuff together
>> colourMapper->SetLookupTable( overlayLUT );
>> colourMapper->SetInput( binConnector->GetOutput() );
>> overlayMapper->SetInput( colourMapper->GetOutput() );
>> overlayActor->SetMapper( overlayMapper );
>> overlayRenderer->AddActor( overlayActor );
>>
>> // Connect everything together
>> renWin->SetSize( size[0], size[1] );
>> renWin->SetNumberOfLayers( 2 );
>> renWin->AddRenderer( imageRenderer );
>> renWin->AddRenderer( overlayRenderer );
>> imageRenderer->SetLayer( 0 );
>> overlayRenderer->SetLayer( 1 );
>>
>> // Look at the pretty picture!
>> renWin->Render();
>> interactor->Start();
>> _______________________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>>
>> Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
>>
>> Follow this link to subscribe/unsubscribe:
>> http://www.vtk.org/mailman/listinfo/vtkusers
>>
>
>
>
> --
> Jeff Baumes, Ph.D.
> R&D Engineer, Kitware Inc.
> (518) 371-3971 x132
> jeff.baumes at kitware.com
>