[vtkusers] vtkImageBlend -- what are permissible input pixel types?

[kent williams]

I now know what does not work -- if you pass in images with a scalar
type of float, vtkImageBlend throws this error message:

ERROR: .../VTK/Imaging/vtkImageBlend.cxx, line 1055\nvtkImageBlend
(0x863e0f0): Execute: input1 ScalarType (10),
must match output ScalarType (3)

There's no way to set the preferred image type for vtkImageBlend, so
I'm guessing it always uses unsigned char as an image type.  The
Doxygen page isn't much use:

vtkImageBlend takes L, LA, RGB, or RGBA images as input and blends
them according to the alpha values and/or the opacity setting for each
input.

What pixel type is 'L'  From looking at the error message and source
code, it seems L ALWAYS has to be unsigned char.

If that's the case, then it's probably a good idea to document it.