[vtkusers] Difficulty on creating a LookupTable

[Alessandro]

Hello,

I'm trying to create a lookuptable to map values by range into colors and opacity. Let's use some number to be clear:

values from 0.0 to 0.2 -> transparent
values from 0.2 to 0.3 -> yellow
...
values from 0.9 to 1.0 -> white

Is there a way to do this through the vtkLookupTable and  vtkImageMapToColors? I tried everything (almost all example I could find) but i cannot understand how to set the mapping...

Thanks, 
Ale