def RGB_to_Y(image):
    """ Image has values from 0 to 1. """
    R = image[:, :, :, (0)]
    G = image[:, :, :, (1)]
    B = image[:, :, :, (2)]
    Y = 16 + 65.738 * R + 129.057 * G + 25.064 * B
    return Y / 255.0
