[vtkusers] vtkFixedPointVolumeRayCastMapper,dark background

[petr zlamal]

Hi vtkusers,
I have problem with vtkFixedPointVolumeRayCastMapper(). If I use a 8bits 
bmp image data on input. The finally rendered scene (by using vtkVolume) 
has a dark (black) background. If I use 16 bits png on input is all right.

Any suggestion?

Thank you
Vepro