MedicalVisualization

Gradient-Magnitude DVR Technique

Lighting | | GradMag and MR

The gradient magnitude technique modulates the emission and absorption coefficients with the absolute value of the gradient vector (gradient magnitude).

Occuring effect: If the volume function is constant, the gradient is zero, so that the volume is rendered transparently. The gradient magnitude technique only shows interesting parts of the volume, that is the material boundaries between materials with different scalar values.

With and without GradMag:

WGradMag WOGradMag

Advantages:

  • Automatic iso surface extraction at material boundaries.
  • No manual tweaking of the TF, a linear one already does the job.
  • No explicit extraction of geometry required (compared to iso surfacing).

Disadvantages:

  • GradMag emphasizes noise.
  • This means, that air needs to be windowed.
  • The gradient vector needs to be precomputed and represented as a second 3D texture, taking up much more memory on the graphics card.


Lighting | | GradMag and MR

Options: