Monochromatic Vision

Black and White (Monochromatic) Vision

Most crepuscular (active at dawn or dusk) or nocturnal animals have monochromatic vision. This means they have only one type of visual receptor in their retina, which responds to the presence of absence of light energy. Under low levels of light, humans vision is monochromatic, using receptors called rods. Objects reflect different wavelengths of light and different amounts of light. Even if an animal has only one type of visual receptor, differently colored objects will produce "pictures" which the animal can discrminate. This example, of a seahorse photographed against a colored background, shows that in a monochromatic rendition, contrast between the light and dark areas preserves an interpretable image.