VolumeRendering

Transfer Functions

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Recap: A Transfer function (TF) assigns emission and absorption coefficients to each specific scalar value $s$.

Linear default behavior of a gas:

$ TF_A(s)=\mu_A \cdot s $
$ TF_{RGB}(s)=\mu_E \cdot s $

with global emission and absorption coefficients $\mu_A$ and $\mu_E$.

A non-linear assignment is realized as

  • lookup table
  • union of line segments.

Pre-multiplication: implicit multiplication of the emission coefficients with the respective absorption coefficients:

$ TF_{RGB}'(s) = TF_{RGB}(s) \cdot TF_A(s) $

Note: The over-operator automatically realizes pre-multiplied alpha values, since the fragment color is multiplied with the fragment opacity.

Display of transfer functions in the TF Editor as normalized unit function curves $\kappa(s)$ and $\rho(s)$ on the unit domain $s, \rho(s), \kappa(s)\in[0,1]$:

$ TF_A(s) = \rho(s) \mu_A $
$ TF_{RGB}(s) = \kappa(s) \mu_E $


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