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Texture
Paletted Texture: This check box only
affects texture map rendering. Note: Paletted textures are not
available on all graphics boards. When possible, create "color index" textures
using one byte per voxel. This minimizes texture memory used, minimizes the
texture loading time and allows dynamic modification of the color map. If not
checked, or not possible, we create "RGBA" textures using four bytes per voxel.
Note:
If fragment programming is supported on the graphics board, a fragment
program will be used for the color table mode instead of paletted texture.
Compressed Texture:
Controls use of the OpenGL texture compression extension (if available). A
significant advantage of compressed textures is that they conserve texture
memory space. Currently, the extension works on RGBA textures only, not on
paletted textures. The compression factor is about 5.
Shared Texture:
Controls use of the OpenGL shared texture paletted extension (if available).
On machines that support paletted textures, using a shared palette conserves
texture memory because a single palette can be used for all textures.
Composition: This pulldown selects the
image composition method. Alpha blending is the most common method. "Max" or
Maximum Intensity Projection (MIP) is also useful. Note:
When using texture map rendering, MIP is only approximately correct.
Here is a picture showing the use of MIP composition:
Interpolation:
This pulldown allows to choose between "Linear" (linear interpolation), "Nearest"
(nearest neighbor) and "Multisample (12 samples)"
(high quality interpolation for slices and volume skin)
texture mapping modes.
rendering.
Render Method: This pulldown selects a
rendering method from the following list:
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Auto: Automatically choose the best available rendering method in the same
order as these items.
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3D Texturing: Use OpenGL 3D texture mapping (if available).
If available, provides good performance and good image quality, especially when
"View Aligned Slices"
is selected. Image quality is enhanced compared to 2D texture mapping because
the graphics hardware performs interpolation along all three axes. Boards known
to support 3D texture mapping include Sun Expert3D, Intense3D Wildcat, and HP
fx series.
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2D Texturing: Use OpenGL 2D texture mapping.
Available on all machines, provides good performance and fair image quality.
Switching between 2D and 3D texture mapping will incur a delay while the
textures are loaded into the graphics hardware.
Rendering style
The volume can be rendered in different styles: standard volume
rendering, pre-integrated volume rendering, lighted volume rendering, lighted
pre-integrated volume rendering,
isosurfaces (only voxels of a given value are rendered), a skin (only
outside faces of the volume cube are rendered), or an RGBA skin (RGBA textures are used
rather than indexed textures).Note: Programmable shader support is
required for the pre-integrated and isosurface rendering styles.
Geometry Control
View-Aligned Slices:
This check box only affects 3D texture map rendering. By default, slices are
aligned with the axis (X, Y, or Z) closest to the direction of view (like 2D
texture map rendering). "View-aligned" means slices are drawn perpendicular to
the direction of view. This is a little slower, but produces a better image.
Number of Slices: This slider controls the
number of slices drawn for 3D and 2D-Multi texture map rendering. Zero means to
automatically select the number of slices. Rendering fewer slices will
generally improve performance (with reduced image quality). An application
might want to reduce the number of slices drawn during interactive operations.
LowRes Move: Enabling this option decreases the resolution of the screen
when the user is interacting with the volume. It decreases the resolution only for
the volume and not for the surrounding objects.
Optimisation: By setting this to "All", all available volume rendering
optimisations are enabled. The "Expert" mode allows a finer control by enabling optimisation
independently. Some of these optimisations needs hardware support (GLSL shaders and framebuffer
objects).
earlyZ: If enabled, stop computing when the pixel's cumulative opacity reaches 1.
This can increase performance when an expensive shader is being used.
GPU vertices: Slice vertices used for volume rendering are generated by the GPU instead of the
CPU. This can increase performance when a large number of slices is being used or when
"Subtiles" is enabled.
SubTiles: LDM tiles will be subdivided for rendering. Fully transparent sub-tiles won't
be rendered, thus increasing the speed of the rendering if an
expensive shader is being used. You should enable "GPU vertices" to TRUE when
using this option.
Edge Enhancement
Edge coloring: If enabled, changes the color based on the gradient direction (normal).
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
black.
Threshold: If this value is low, more edges (and possibly noise) will be detected.
Edge 2D: When enabled, a 2D edge detection algorithm is used
to highlight edges in the rendered image of the volume.
Inner edges: Increase this value to decrease noise on silhouette edges
Outer edges: Increase this value to decrease noise on edges in the volume.
Boundary Opacity: Increases boundary opacity based on the gradient magnitude.
Boundary Opacity's threshold: If this value is low (near 0.), only regions with a high gradient will be enhanced.
Intensity: If greater than 1, this increases the boundary opacity globally. Otherwise it decreases it.
Volume Skin
Bump Mapping: If enabled, changes the color based on the gradient direction (normal).
Bump Scale: Controls the magnitude of the bump
Material and Lighting
Lighting: The check box controls a
directional light, initially aimed at the volume from the +Z axis. This light
rotates with the volume. Using texture map rendering, lighting is approximated.
Note:
Turning the light on and off or changing the light direction may require
reloading textures, which is slow. Using shaders (lighted volume rendering in Rendering
style dialog) the light can be dynamically modified.
Volume with lighting enabled:
Light Editor:
The "Light Editor" button brings up the standard Open Inventor directional
light editor. The gray sphere shows how the light will shine on the volume. The
yellow arrow shows the current direction of the light. You can "grab" this
arrow with the mouse and drag it to change the light direction. When you are
finished with the editor, just click the "X" button in the window banner to
close it.
Material Editor:
This button brings up the standard Open Inventor material editor. In this
demo, the material editor controls the diffuse, specular, etc., properties of
the volume. In the case of texture map rendering, it specifically controls the
properties of the polygons that are textured.
Global Alpha: This slider controls a scale
factor
that is applied to all the Alpha values in the color map before color lookup
occurs. When the slider is set to 1.0, voxels have exactly the alpha value
specified by the color map. Moving the slider to the left makes the entire
volume progressively more transparent. Unlike modifying the colormap, this is
an interactive operation even for texture map rendering. When the check box to
the left of the slider is "checked", the global alpha value is updated
dynamically as the slider moves. Otherwise the value is only updated when you
release the mouse button after moving the slider. You can also type a value in
the edit box.
Picking (Probe): This check box toggles volume/slice
picking mode and visibility of the pick profile
window. To use picking, first make sure the Main Window has focus (click
in it if necessary), then make sure the viewer is in selection mode (cursor is
an arrow shape).
The Pick Profile window looks like this:
Picking on an ortho slice or oblique slice selects the closest voxel to the
selected point. It returns the value of the selected voxel, its I,J,K position
in the volume, and its X,Y,Z position in the 3D scene (not shown here).
Picking on a volume selects the first opaque voxel along the pick ray. It
returns the value of the selected voxel, its I,J,K position in the volume, and
its X,Y,Z position in the 3D scene (not shown here). Optionally it can also
return the "profile" along the pick ray, which is a list of the values of all
the voxels intersected by the pick ray (shown in the figure above as a line
graph).
Isosurfaces
The following items are only active when the rendering
style is Isosurface.
Number of Isosurfaces to Create: This
allows you to to specify how many isosurfaces should be created.
Select Isosurface to Control: This
allows you to to specify which isosurface to control.
Isovalue: This slider
allows you to to specify the isovalue for the selected isosurface.
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