MedicalVisualization

## Transfer Functions

A transfer function, is a generalized concept of color-mapping, where the transfer function assigns physical properties $p$, such as colors $rgb$, to scalar values $s$.

$TF(s) = p$

Linear transfer functions are realized by a global mapping coefficient:

$TF(s)=\mu \cdot s$

The mapping to Hounsfield values is a special case of linear mapping with a scale- and offset-factor:

$TF(s)=\mu \cdot s + o$ with $\mu=1000/0.15cm^{-1}, o=-1000$

A non-linear assignment is represented as

• threshold function → $TF_t(s) = 1: s>t, 0: else$
• lookup table
• union of line segments.

Display of transfer functions in the TF Editor as normalized unit function curves, e.g. with gimp “Freehand Curves”: