[vtkusers] Clear / update function for vtkImageMapToRGBA

[rkemp]

Hi,

I've a little program which visualizes a calculation each time step. I use the ImageViewer object to 
display it.

I) If I render the ImageData directly the visualization behaves just as expected (grayscale)

II) However if I render it using with a vtkImageMapToRGBA filter in order to get a colored 
visualization, only the first rendering appears. New renderings don't appear, because the first one 
is still there. If I only render the last rendering, it is exactly the colored visualization I expect.

My question: Do you have to use some clear operation or something in situation II? Which function 
should do that??

Thank you very much for your comments!!

Roelof