Just wanted to let the community know that vtkResizingWindowToImageFilter does not appear to properly handle the alpha channel. Setting SetInputBufferTypeToRGBA does not add a 4th element to the output. This was annoying for me since I wanted to render an image with a transparent background.
It turns out that under the hood this filter just uses a vtkWindowToImageFilter, so you can just copy the code vtkResizingWindowToImageFilter uses to do the scaling computation and use vtkWindowToImageFilter directly.
