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Volume Rendering
Using transfer function editor.
sargis
This tutorial introduces 3D Grid/Volume Rendering widget and explains how to use it.
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If you have GL_EXT_texture3D, ARB_texture_cube_map or similar
OpenGL extensions, which most of the modern graphics boards do, you should see VolRender
button next to OrthoSlice. Click on this button to open transfer
function editor. The X-axis in this widget is the value of the scalar
field mapped to [0,255] range. The Y-axis describes how transparent the
grid point with a given scalar value should be drawn. The default
transfer function is a ramp, which means that the grid points with
low values are transparent and the ones with high values are
opaque. Drag the dots to modify the opacity and see how it effects the
final image. The transfer function is stored internally as color and
opacity lookup table (LUT).
To change the color in this LUT select a dot, right-click to open a
menu shown on the left and use
Set color option. The menu also has other options such as
Reset, Draw function (ramp or reversed ramp),
Flip function, etc. Middle-clicking (alt/Option on Mac) and dragging a dot will move the
entire transfer function. Double-clicking on lines adds a new dot and
Shit-click adds new set of four dots.Designing GUI for a transfer function is a challenging task, but we hope that you'll find this tool useful. |
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