If this sounds too complicated, don't bother. The renderer works fine without indexing. If you are rendering MRIcro regions or SPM volumes, first open that volume and select it here. If you want to do indexing and select a volume here, make sure you choose an appropriate Classifier. If you want to depth code your renderings, create a ramp stack of the same width, height and depth of your volume stack using Depth Coded Stack , select the Volume Renderer , and select that stack here.
Scale sets the enlargement of the volume.
If an aspect ratio is present in the volume stack they are set automatically. Classifier allows a choice of classification algorithms, the functions that decide the visibility, color and opacity of voxels. G radient classifiers use a combination of the voxel gradient and the voxel value. The boundaries between two materials or tissues in volumes rendered with these classification functions will show as hard surfaces. There is a choice of indexing and non-indexing classifiers.