private void WritePNG(string filePath)
{
vtkRenderWindow renW = myRenderWindowControl.RenderWindow;
vtkRenderer ren = renW.GetRenderers().GetFirstRenderer();
double [] backCol;
backCol = ren.GetBackground();
ren.SetBackground(255.0, 255.0, 255.0);
vtkRenderLargeImage largeScreenExpoHelper = vtkRenderLargeImage.New();
largeScreenExpoHelper.SetInput(ren);
largeScreenExpoHelper.SetMagnification(10);
vtkPNGWriter writer = vtkPNGWriter.New();
writer.SetFileName(filePath);
writer.SetInputConnection(largeScreenExpoHelper.GetOutputPort());
writer.Write();
ren.SetBackground(backCol[0], backCol[1], backCol[2]);
}