[vtkusers] 16Bit per color channel?

[Sophonet]

Hi list,

using OSMesa for offscreen rendering (and VTK 8.1.0) I would like to 
save the renderwindow content (vtkWindowToImageFilter) with 16 bits per 
color channel to file. PNG would support 16 bits per channel 
(https://en.wikipedia.org/wiki/Portable_Network_Graphics), but I am 
wondering how to set things up via VTK. Any hint?

Thanks,

     sophonet