How to take a screenshot when using non linear imager?

I’m struggling to take a screenshot with a non linear imager used for a fisheyelens (see FisheyeLens for distortion).

In the past, for simple display region and cameras I’ve done the following with success

ramImage = display_region.get_screenshot().getRamImageAs(pixFormat)
pixFormat = "BGR"
data = memoryview(ramImage)
width = display_region.get_pixel_width()
height = display_region.get_pixel_height()
return np.reshape(data, (height, width, 3))

but using this for the display region attached to the non linear imager just yields a gray screenshot.