VolumeRendering
Emission and Absorption
Optical Model of a self-emitting gas with simultaneous emission and absorption:
Linear transfer functions TFA=μAs resp. TFE=μEs.
Realization of numerical integration with OpenGL: Numerical integration by view-aligned slicing with slice distance Δt with Over-Operator and constant vertex opacity 1−e−μAΔt, constant vertex color (μEΔt,μEΔt,μEΔt) and modulation of vertex color with 3D-texture lookup of s(t).
Ambient background emission needs to be enabled.
Non-linear transfer function TFE=κ(s(t)) allows masking and coloring of specific materials (using a TF Editor):
Advantages:
- Self Emission of objects adds to background emission → better contrast.
- Objects can occlude each other partially or completely depending on their opacity.
- → very good depth perception.
Disadvantages:
- non-commutative
- View-aligned slices need to be rendered in back to front order!
Vertex color:
glColor4f(muE*dt,muE*dt,muE*dt, 1-exp(-muA*dt));
3D texture modulation:
glEnable(GL_TEXTURE_3D);
glTexEnvi(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_MODULATE);
glTexEnvi(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_MODULATE);
Over-operator with OpenGL-blending:
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);
glEnable(GL_BLEND);