'Return the total intensity from the red, blue, and green intensities.
This is a naive computation, and may be overridden by subclasses.
Parameters
image_r : `~numpy.ndarray`
Intensity of image to be mapped to red; or total intensity if
``image_g`` and ``image_b`` are None.
image_g : `~numpy.ndarray`, optional
Intensity of image to be mapped to green.
image_b : `~numpy.ndarray`, optional
Intensity of image to be mapped to blue.
Returns
intensity : `~numpy.ndarray`
Total intensity from the red, blue and green intensities, or
``image_r`` if green and blue images are not provided.'

def intensity(self, image_r, image_g, image_b):

    return compute_intensity(image_r, image_g, image_b)
