Alpha compositing (Default).

Also called Direct Volume Rendering (DVR) it blends the R, G, and B components for each data value along the sampling ray based on the alpha value (alpha blending).

Minimum intensity projection (MinIP).

The minimum value found along each ray is used to determine color.

Maximum intensity projection (MIP).

The maximum value found along each ray is used to determine color.

Ray sum intensity projection (RSP).

The values found along each ray are accumulated. Then the total value is normalized by the nominal number of samples for every ray (see OIV.VolumeViz.Nodes.SoVolumeRender.numSlices), which is the same for all rays. The values seen in shader functions, e.g. VVizComputeFragmentColor are still in the range 0..1, but the range of values that represents is quite different from the voxel data range.

Average Intensity projection (AIP).

The values found along each ray are accumulated. The total value is divided by the actual number of samples along the current ray. The actual number of samples may be different for each ray. The resulting data range will be similar to the voxel data range but not necessarily the same. If there are many low, e.g. 0, valued voxels, the average may be very small.

Maximum Intensity Difference Accumulation (MIDA).

Assuming the important features of the volumetric datasets are of high scalar values, this mode changes the compositing behavior by decreasing the accumulated color and opacity when the incoming sample's scalar intensity is higher than any of those before it along the viewing ray. In this way, the high scalar value features in the volumetric datasets won't be occluded as much as in a standard compositing (i.e. VOLUME_RENDERING).

See Instant volume visualization using maximum intensity difference accumulation. Stefan Bruckner and M. Eduard Groller. 2009. In Proceedings of the 11th Eurographics / IEEE - VGTC conference on Visualization (EuroVis'09) for details.

Intensity Difference Accumulation.

This mode acts as MIDA but only the opacity of the accumulated color is affected and the modulation is based on the intensity difference of two consecutive samples. This mode should emphase the difference between two different structures with different scalar intensities.

See Fast Volumetric Data Exploration with Importance-Based Accumulated Transparency Modulation. Wan Yong and Hansen Chuck, 2010, IEEE/ EG Symposium on Volume Graphics for details.

Maximum Gradient Difference Accumulation.

This mode acts as INTENSITY_DIFFERENCE_ACCUMULATION but the composition is affected when the incoming sample's gradient is higher than any of those before it along the viewing ray. It aims at revealing important features (i.e. higher gradient transitions) all along the ray direction.

Gradient Difference Accumulation.

This mode acts as MAX_GRADIENT_DIFFERENCE_ACCUMULATION but the opacity modulation is based on the gradient difference of two consecutive samples. It leads to a more transparent result, as more samples along the viewing ray contribute to the final result.