Computer Vision (5)

If you closely observe the different species in the animal kingdom you will see that there are two kinds of creatures. Ones, that do perceive depth through vision and others that don’t. The ones that don’t will have their eyes towards the sides. Haven’t seen such a creature? Give a deep thought, you would have even painted them in your childhood drawing classes. Fishes have their eyes towards the sides and hence cannot perceive depth. Then how do they move about, you were finding it very difficult with just one eye open? Won’t their survival get affected from it? Not really! Instead it is evolution that has given them such an eye sight just for survival.

In general the observation is this; predators have their eyes towards their front and prey will have them on their sides. Let’s take the ferocious tiger for instance. A tiger needs to pounce on its prey exactly and can’t use the trial and error method that you used to catch hold of the wire :) (refer my earlier post). To take a decision it needs to know the exact location of its prey which is given by depth. For a prey on the other hand, it is enough to know the presence of the predator, its exact location takes a low priority. For the predator its focus is on the prey and not the surrounding, for a prey its focus is on the surrounding, because it needs to look out for any possible danger from all sides. Evolution has hence given a predator a narrow angle vision but an overlapping one to perceive depth, while the prey has a much wider angled vision but lacks depth.

This does not mean that a prey does not have depth perception at all, it is just that wide angle is more important than depth. So the overlapping region is very small between the two eyes. Its face is designed in that way. We for example, along with say a tiger and other predators have a flatter face to hold both the eyes on the front, while a deer for example has a curved face so that their eyes are somewhat towards the sides. There is also a special case, creatures that play a dual role of predator and prey. Chameleons have adjustable eye sockets. When they sense danger the sockets move towards the sides to get a wider look, and while hunting they come closer to get an overlapped view! In the overlapped view both the eyes look at the same object while in the independent view they can process the two images separately. In our case that is not possible. Even though we have two eyes we cannot see two different objects at the same time, our eyes cannot move independent of each other.