Volume rendering modes

The primary volume rendering mode is, of course, direct volume rendering as described in the preceding sections. However the volume rendering engine is able to generate useful UserGuide_Images using several other rendering modes in place of volume rendering.

Isosurface rendering can be enabled using the SoVolumeIsosurface node or the SoVolumeDataDrawStyle node. The SoVolumeRenderingQuality field voxelizedRendering enables a rendering mode called voxelized rendering. The SoVolumeDataDrawStyle field style can also enable a special mode called “mask boundary rendering” when using SoVolumeMask nodes.

In this section we will discuss:

• Alternate compositing (e.g. Maximum Intensity Projection)
• Voxelized rendering
• Isosurface rendering
• Mask boundary rendering

Alternate Compositing

Compositing controls how the color and opacity of the sample points along each ray are combined to form the final image. The method to be used is specified using the renderMode field of SoVolumeRender. The default, and most common, composition method is ALPHA_BLENDING. The available composition methods are:

• VOLUME_RENDERING

Blends the computed color for each data value along the view projection ray based on the alpha value

• MIN_INTENSITY_PROJECTION

Draws the color associated with the minimum data intensity along the view projection ray

• MAX_INTENSITY_PROJECTION

Draws the color associated with the maximum data intensity along the view projection ray

• SUM_INTENSITY_PROJECTION

Draws the color associated with the sum of all data values along the view projection ray

• AVERAGE_INTENSITY_PROJECTION

Draws the color associated with the average of all data values along the view projection ray

• MAX_INTENSITY_DIFFERENCE_ACCUMULATION

Combine the advantages of direct volume rendering and maximum intensity projection

This is an alternate composition algoritm, not a projection, so volume rendering parameters apply

See this publication

• INTENSITY_DIFFERENCE_ACCUMULATION

Combine the advantages of direct volume rendering and accumulated transparency modulated by intensity increase

• MAX_GRADIENT_DIFFERENCE_ACCUMULATION

Combine the advantages of direct volume rendering and accumulated transparency modulated by maximum gradient magnitude

• GRADIENT_DIFFERENCE_ACCUMULATION

Combine the advantages of direct volume rendering and accumulated transparency modulated by gradient magnitude increase When using a compositing mode other than VOLUME_RENDERING, only raycasting mode is supported and no depth information is retained.

Composition modes:

"Important"

• When not using volume masks, the draw style node must be traversed before the SoVolumeData node.
• The MASK_BOUNDARY style is ignored if not using volume masks.
• The ISOSURFACE style is functionally equivalent to using an SoVolumeIsosurface node.