[vtkusers] vtkWindowToImageFilter / vtkPNGWriter produces black images under Vista

[Barry Hathaway]

I'm trying to save a rendered image to a PNG file and the result is all 
black under Windows Vista 32-bit
on my laptop.  The same code works fine under Window XP.  This is with 
VTK 4.4.
The TCL code snippet is:

            global estimateWindow
            catch {vtkWindowToImageFilter windowToImage}
            windowToImage SetInput $estimateWindow
            windowToImage Modified
            catch {vtkPNGWriter imagePNGWriter}
            imagePNGWriter SetInput [windowToImage GetOutput]
            imagePNGWriter SetFileName $filename
            imagePNGWriter Write

I get the same result if I replace vtkPNGWriter with vtkJPEGWriter.
Any ideas how to proceed?  I'd prefer not to upgrade VTK with the 
possible exception of the
offending modules.

I did notice this problem was mentioned about a year ago on the list 
with no resolution.
Thanks.

Barry Hathaway