openmv support

hi,

it seems that openMV difference() and get similarity() are not implemented or I am doing something wrong. it’s running on the 4.0.50 firmware (latest to date)

img_previous = sensor.snapshot()         # Take a picture and return the image.

while(True):
    clock.tick()                    # Update the FPS clock.
    img = sensor.snapshot()         # Take a picture and return the image.
   # img_previous = img

    img_res = img.difference(img_previous)

    #sim = img.get_similarity(img_background)
    #change = "- Change -" if sim.min() < MIN_TRIGGER_THRESHOLD else "- No Change -"
    #print("Change =",sim, change)

    lcd.display(img_res)  

any idea?

thanks in advance