[vtkusers] question regard transparency

[Benjamin King]

Hi Luke,

> I try to use vtk to generate brain contours from MRI scan image and try 
> to make the brain surface transparent. But once I set the surface to 
> transparent, there is some white matters apears in the scene. And I can

it's only a wild guess, but do you include a vtkDepthSortPolyData filter 
somewhere in your pipeline? It may be that the contouring produces the 
heavily folded surface correctly but the rendering looks funny because the 
polygons aren't sorted prior to the rendering. This is (only) necessary for 
partially transparent polydata.


> not make it transparent as well. See the picture in the attachment.
> Does anyone know how to eliminate those white materials?

If you want to get rid of smaller components that are not connected to the 
largest, you can use vtkPolyDataConnectivityFilter.


> I have an idea which is to delete the polygons in the back. Is it 
> feasible, and which filter should I use?

If by 'in the back' you mean all the polygons that are behind other ones, 
why whould you use transparency then? But maybe I don't understand. Anyway, 
take a look at vtkProperty::SetBackFaceCulling(int). I don't know if the 
contouring process generates the normals you need for the culling, so you 
might also need to apply the vtkPolyDataNormals filter first.

Hope it helps,
  Benjamin



-- 
Benjamin King
Institut für Medizinische Informatik
Medizinische Hochschule Hannover
Tel.: +49  511  532-2663