import - How do I convert imported STL files to 3D images?

After importing a 3D image in STL format, my possibilities in regard to "3D Volumetric Image Processing" seem rather limited. All examples are given with TIFF files. Is there a way to convert from STL to TIFF or work with an STL image in some other way?

Answer

Here is something quick and dirty to convert from a Graphics3D to Image3D (the second argument is sort of a quality knob, the higher the number the more slices are taken):

img3Dify[gr3d_Graphics3D, qu_] := Module[{pr, br, slices},
  pr = PlotRange /. AbsoluteOptions[gr3d, PlotRange];
  br = Map[Norm@Differences[#] &, pr]; 
  slices = ParallelMap[
    Image[Show[gr3d, ViewPoint -> Top, 
       Lighting -> {{"Ambient", White}}, Background -> None, 
       PlotRange -> {pr[[1]], pr[[2]], #}]] &, 
    Partition[FindDivisions[pr[[3]], qu*2], 2, 1]];
  Image3D[slices, BoxRatios -> br, ColorFunction -> Hue]]

on an example image

spikey = Import["ExampleData/spikey.stl", "Graphics3D"]

img3Dify[spikey, 40]