Returns an image array of current render window

def image(self):
        """ Returns an image array of current render window """
        if not hasattr(self, 'ren_win') and hasattr(self, 'last_image'):
            return self.last_image
        ifilter = vtk.vtkWindowToImageFilter()
        ifilter.SetInput(self.ren_win)
        ifilter.ReadFrontBufferOff()
        if self.image_transparent_background:
            ifilter.SetInputBufferTypeToRGBA()
        else:
            ifilter.SetInputBufferTypeToRGB()
        return self._run_image_filter(ifilter)