DVR Shading

ITK VTK Integration | | Gradient Magnitude

How can a volume be shaded?
Problem: We do not have an explicit triangle mesh that could supply normals for shading operations.

Solution: Lighting of the volume by modulation of emission according to the Blinn Phong shading-model: The surface normal is substituted for the normalized gradient vector of the volume. This effectively simulates the shading of iso surfaces without explicitly extracting those.

Head-light with ambient, diffuse, and specular terms of the Blinn-Phong shading model:

images by Christop Rezk-Salama and Peter Hastreiter

Advantage of shading:

  • specular lighting reveals surface structures:
  • still interactive compared to iso surface extraction
Illu-Example1 Illu-Example2

Disadvantage of shading:

  • transparency lessens the contrast of shaded surfaces
  • rendering artefacts due to non-linear transfer functions → pre-integration

ITK VTK Integration | | Gradient Magnitude