Setting scalar range in vtkPolyDataMapper - vtkLookupTable vs vtkColorTransferFunction

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Hi

I am trying to setup a poly mapper with a lookup table or a color transfer function.

If I use a lookup table, then setting the SetScalarRange is used if UseLookupTableScalrRange is False and not when UseLookupTableScalrRange is true, which is according to what the vtk documentation says.

lut= vtk.vtkLookupTable()
mapper.SetLookupTable(lut)
mapper.SetUseLookupTableScalarRange(true/false)
mapper.SetScalarRange(min, max)

But instead of a lookup table, if I try to use a color transfer function, then setting the scalar range has no effect, irrespective of if the UseLookupTableScalrRange is true or false.

ctf= vtk.vtkColorTransferFunction()
mapper.SetLookupTable(ctf)
mapper.SetUseLookupTableScalarRangeOn(true/false)
mapper.SetScalarRange(min, max)

What am I missing here, or is that a bug?

Thanks
Ashish