This property node causes subsequent OIV.VolumeViz.Nodes.SoVolumeRender nodes to be drawn with different rendering effects and/or levels of quality.

NOTE:

• Only one (or none) of the following nodes can be active at a time: OIV.VolumeViz.Nodes.SoVolumeShader or OIV.VolumeViz.Nodes.SoVolumeRenderingQuality. However since Open Inventor 7.1, both OIV.VolumeViz.Nodes.SoVolumeRenderingQuality and OIV.VolumeViz.Nodes.SoVolumeIsosurface may applied to the same OIV.VolumeViz.Nodes.SoVolumeRender node.

• If the application simply needs to replace one or more of the VolumeViz shader rendering functions with a customized shader, you can use either OIV.VolumeViz.Nodes.SoVolumeShader or OIV.VolumeViz.Nodes.SoVolumeRenderingQuality. However if the application needs the advanced rendering features of OIV.VolumeViz.Nodes.SoVolumeRenderingQuality, e.g. lighting, in addition to the customized behavior, then you should use this node (which is derived from OIV.VolumeViz.Nodes.SoVolumeShader). Using the shader rendering framework is explained on the OIV.VolumeViz.Nodes.SoVolumeShader page.

• The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality node must be before the OIV.VolumeViz.Nodes.SoVolumeRender and after the OIV.LDM.Nodes.SoTransferFunction.

• This is a shader node! The effect will usually be undesirable if it is applied to standard geometry (polygons, lines, etc). Therefore applications should generally keep the volume visualization nodes and standard geometry nodes separate in the scene graph (i.e. under different OIV.Inventor.Nodes.SoSeparator nodes).

• Please read the comments for each field. Some options have no effect in ray-casting mode (the default) and some options only apply in ray-casting mode. Similarly, some options only apply to gradient lighting and have no effect on deferred lighting.

  Pre-integrated and lighted rendering

  Various enhanced rendering modes for volume rendering are available:

  • Pre-integrated volume rendering

  • Lighted volume rendering

The pre-integrated mode (OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_preIntegrated field) generally provides higher image quality for the same number of slices. Most applications should enable this field. However, note that pre-integration integrates between color map values. For typical scalar data containing sampled values, this provides a beneficial smoothing. It is especially useful when the color changes sharply between adjacent color map entries. However, when the color changes sharply between adjacent voxels, it can can cause values that are not actually in the original data to be displayed. This is undesireable for some data, for example "label" volumes resulting from segmentation. Pre-integration is not recommended for such data. Also note:

• The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_preIntegrated field has no effect on OIV.VolumeViz.Nodes.SoVolumeIsosurface rendering.

• The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_preIntegrated field is only considered when SoVolumeRendering.renderMode is set to VOLUME_RENDERING (the default).

When lighting is enabled for volume rendering, VolumeViz applies the same lighting equation used for polygonal geometry, including (optionally) specular highlights. The base voxel color comes from the OIV.LDM.Nodes.SoTransferFunction node or (optionally) from a custom shader function provided by the application. This color is modified using the current material (OIV.Inventor.Nodes.SoMaterial), a vector simulating a "normal vector" and one or more directional light nodes (OIV.Inventor.Nodes.SoDirectionalLight) found in the scene graph. Voxels can also cast and receive shadows (see OIV.Inventor.Nodes.SoShadowGroup).

Limitation: Pre-integrated and lighted rendering are not supported if using custom fragment shaders and redefining FRAGMENT_COMPUTE_COLOR slot.

VolumeViz supports two lighting modes using either the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_lighting field or the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_deferredLighting field. In both cases lighting is computed on the GPU as part of the rendering process. (Do NOT use the lighting field in the OIV.VolumeViz.Nodes.SoVolumeRendering node. This field enables a CPU lighting computation that is slow.)

• Gradient lighting The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_lighting field enables gradient based lighting, where the "normal vector" at each sample along the ray is a gradient vector computed from the data values in the volume. Gradient based lighting only supports a single light source and only the first light in the scene graph (typically the viewer's "headlight") is used. No other lights affect the volume in this case. The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_gradientQuality field controls the algorithm used to compute gradient vectors. Several other fields affect the gradient computation including OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_gradientThreshold, OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_surfaceScalarExponent and OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_unnormalizedGradientExponent. Setting surfaceScalarExponent to a small value, for example 2.0, is recommended.

• Deferred lighting The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_deferredLighting field enables screen space lighting, where the "normal vector" is computed from the final image depth buffer. Deferred lighting is faster and supports multiple light sources, but works best when the transfer function makes each data value either opaque or transparent. Deferred lighting is not affected by gradient related fields.

Unlike other primitives (including other VolumeViz primitives), volume lighting is not affected by an OIV.Inventor.Nodes.SoLightModel node. Also unlike other primitives, if lighting is enabled and there are no light nodes in the scene graph, the voxel color is taken from the transfer function or custom shader function "as is" (other primitives would be black in this case).

Each light node's direction and intensity fields are used, but the color field is not currently used. The current OIV.Inventor.Nodes.SoMaterial specifies the ambient, specular, diffuse, and emissive color values for the lighting equation. Note that the default diffuse color is "light gray" (0.8), not full white. This allows specular lighting to push the color toward full white (as expected). If specular lighting is not desired, then changing this to full white (1.0) is recommended in order to see the true colors specified in the transfer function.

The following figures show the same volume data:

<TABLE border=1 cellspacing=0 cellpadding=5>
  <TR><TD valign=_top> Default volume rendering  <TD valign=_top> Pre-integrated volume rendering  <TD valign=_top> Lighted pre-integrated volume rendering
  <TR><TD valign=_top> @image html quality_volume.jpg
            <TD valign=_top> @image html quality_preintegrated.jpg
            <TD valign=_top> @image html quality_light.jpg
</TABLE>

Quality enhancement parameters

Jittering: When OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_jittering is set to true, a random offset is added to texture coordinates in order to decrease "ring" artifacts without the cost of drawing a higher number of slices. Note that this creates a "noisy" image. Instead we recommend setting the OIV.VolumeViz.Nodes.SoVolumeRender.m_samplingAlignment field to BOUNDARY_ALIGNED.

  <TABLE border=1 cellspacing=0 cellpadding=5>
    <TR><TD valign=_top> No Jittering  <TD valign=_top> With Jittering
    <TR><TD valign=_top> @image html volume_nojitter.jpg
    <TD valign=_top> @image html volume_jitter.jpg
 </TABLE>

Gradient quality: When gradient lighting (OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_lighting field) is enabled, the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_gradientQuality field allows you to choose between various gradient computation techniques. The computational cost increases with the quality. Has no effect on deferred lighting.

  <TABLE border=1 cellspacing=0 cellpadding=5>
    <TR><TD valign=_top> Low quality  <TD valign=_top> Medium quality  <TD valign=_top> High quality
    <TR><TD valign=_top> @image html volume_forwarddiff.jpg
    <TD valign=_top> @image html volume_centraldiff.jpg
    <TD valign=_top> @image html volume_sobel.jpg
 </TABLE>

Surface scalar: When gradient lighting (OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_lighting field) is enabled or OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeDetect2DMethod is GRADIENT, the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_surfaceScalarExponent field disables lighting (or edge detection) on uniform surfaces in order to avoid noise in these area. This field should not be mixed with OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_unnormalizedGradientExponent. The default value is zero, but a small value, for example 2.0, is recommended. Has no effect on deferred lighting.

  <TABLE border=1 cellspacing=0 cellpadding=5>
    <TR><TD valign=_top> Surface Scalar disabled   <TD valign=_top> Surface Scalar enabled
    <TR><TD valign=_top> @image html surfaceScalarOff.jpg
    <TD valign=_top> @image html surfaceScalarOn.jpg
 </TABLE>

Unnormalized gradient : When gradient lighting (OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_lighting field) is enabled, if OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_unnormalizedGradientExponent is not 0, voxels with small gradients will get more contribution from the ambient light than voxels with high gradients. It is similar to OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_surfaceScalarExponent but uses the ambient light instead of the transfer function color for uniform surfaces. Has no effect on deferred lighting.

Gradient threshold: When gradient lighting is enabled, gradients with a length less than OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_gradientThreshold are ignored during the lighting computation. This avoids doing lighting on noise while still lighting important data. In the following screenshots, setting a threshold of 0.1 removed lighting on the noise surrounding the spheres. Has no effect on deferred lighting.

  <TABLE border=1 cellspacing=0 cellpadding=5>
    <TR><TD valign=_top> With #gradientThreshold set to 0  <TD valign=_top> With #gradientThreshold set to 0.1
    <TR><TD valign=_top> @image html volume_gradientThr0.jpg
    <TD valign=_top> @image html volume_gradientThr1.jpg
 </TABLE>

Image enhancement parameters

Various image enhancement techniques are available in this node and in OIV.LDM.Nodes.SoTransferFunction.

• Ambient occlusion The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_ambientOcclusion field enables a rendering technique that simulates self-shadowing of the volume. In other words, the amount of ambient (global) light in the scene reaching each sample is reduced by neighboring voxels. This effect makes it much easier to see the relative depth of features in the volume. Generally we recommend using this effect rather than the following effects. Both lighting and/or shadow casting may also be enabled, but neither is required to use ambient occlusion. This effect works best when the volume data contains surfaces (region boundaries with relatively sharp gradients) or in voxelized rendering mode. In both cases it works best when voxels are either transparent or nearly opaque. If you use ambientOcclusion, you should set the OIV.VolumeViz.Nodes.SoVolumeRender.m_samplingAlignment field to BOUNDARY_ALIGNED to reduce "slicing" artifacts.

• Boundary opacityOIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_boundaryOpacity increases opacity depending on the length of the gradient vector. Areas with large gradient changes will have their opacity increased according to the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_boundaryOpacityIntensity. Note that this option has a significant performance penalty.

• Edge coloring When OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeColoring is on, the color of each voxel may be mixed with the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeColor. Areas where the normal (computed from the gradient) is facing the camera will have an unmodified color, whereas areas where the normal is more perpendicular to the view direction will tend towards OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeColor.

• Edge detection When OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeDetect2D is enabled, an image space filter is applied on the volume rendering image in order to detect edges, which will be highlighted. The results are affected by the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeDetect2DInnerThreshold and OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeDetect2DOuterThreshold fields. The OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_edgeDetect2DMethod bitmask allows to apply the edge detection on the image's luminance, depth and/or gradient. The gradient method may give noisy result, the OIV.VolumeViz.Nodes.SoVolumeRenderingQuality.m_surfaceScalarExponent may help to improve the result in this case. The gradient method has a significant performance penalty.

The following table shows the available edge detection techniques (explanation of faux shading is in OIV.LDM.Nodes.SoTransferFunction):

No Edges	Boundary Opacity	Edge 2D
Edge Coloring	Faux Shading (see OIV.LDM.Nodes.SoTransferFunction)

Because this node is derived from OIV.VolumeViz.Nodes.SoVolumeShader, IVVR_FIRST_RESERVED_TEXTURE_UNIT applies to it. See OIV.VolumeViz.Nodes.SoVolumeShader for more information.

Volume projection

Volume projection (OIV.Inventor.Nodes.SoProjection or derived classes) is incompatible with some options enabled by this node. Do not enable the preIntegrated, jittering or edgeDetect2D fields when using projection.

FILE FORMAT/DEFAULT

VolumeRenderingQuality {

lighting	false
preIntegrated	true
jittering	false
gradientThreshold	0.0001
edgeColoring	false
edgeColor	(0, 0, 0)
edgeThreshold	0.2
boundaryOpacity	false
boundaryOpacityIntensity	1.5
boundaryOpacityThreshold	1.5
edgeDetect2D	false
edgeDetect2DInnerThreshold	0.1
edgeDetect2DOuterThreshold	0.1
edgeDetect2DMethod	LUMINANCE
gradientQuality	MEDIUM
colorInterpolation	true
unnormalizedGradientExponent	0
surfaceScalarExponent	5
segmentedInterpolation	false
segmentedInterpolationThreshold	0.5
voxelizedRendering	false
voxelOutline	false
voxelOutlineThreshold	2.
voxelOutlineWidth	2.
voxelOutlineColor	(0, 0, 0)
ambientOcclusion	false
deferredLighting	true
interpolateOnMove	true

}

ACTION BEHAVIOR

OIV.Inventor.Actions.SoGLRenderAction Sets volume rendering quality parameters in the traversal state.

Reference