[vtkusers] How do I display data bands from RGB image data?

[Carl Trapani]

Hi vtkusers,

I've got a stack of RGB images that I'm displaying using 
vtkContourFilter and vtkPolyDataNormals following the Medical2.cxx 
example, but I don't think this is the best choice for visualizing the 
data because the spots are not contours. A histogram of my data shows 
that it ranges between 51 and 181 grayscale value where grayscale is 
simply (red + green + blue)/3.

Can anyone suggest how I might:
 
1) convert the RGB scalar data into grayscale values according to 
grayscale = (red + green + blue)/3

2) break the resulting grayscale data into three bands, weak (51-94), 
medium (95-138) and strong (139-182)?

2) show these scalar values as spots (spheres?) with a size 
corresponding to the band the scalar falls within, weak->smallest, 
medium->medium, strong->largest?

Any suggestions would be very welcome.

Thanks in advance,
Carl Trapani