When changing the opacity of a surface, the first step from fully opaque to ‘just a little transparent’ (i.e. from 1.00 to 0.99) causes a relatively big visual difference, whereas the change from 0.99 to 0.98 causes no visible difference. I was looking at a model of the skull generated from the CT of the ‘CT-MR Brain’ sample dataset.
I wonder whether there is a possibility to make the transition between fully opaque and ‘a bit transparent’ smoother?
If your model has a lot of internal structure then you may need to enable depth peeling in order to get predictable rendering.
https://www.slicer.org/wiki/Documentation/4.3/SlicerApplication/MainApplicationGUI#3D_Viewer