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Volume Rendering

Using transfer function editor.


This tutorial introduces 3D Grid/Volume Rendering widget and explains how to use it.
Page 4 of 4.
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.
by Sargis Dallakyan last modified 2007-04-13 09:44 Molecular Graphics Laboratory, TSRI

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