MedicalVisualization

Transfer Functions

Local Thresholding | | Transfer Functions and Iso Values

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”:

GimpTF


Local Thresholding | | Transfer Functions and Iso Values

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