If
you are a fan of photography, you know how difficult it is to take really good pictures. A good picture is the one
that is very well focussed. Auto focus cameras either use IR(active) or contrast enhancement(passive) to focus an
object. Since the objects around us are at different depths, our eye needs to focus at each and every object to give you a
very good view of it. This process is called accommodation. What might the eye been doing during this process? Biologically speaking
the ciliary muscles adjust the tension so as to change the physics of the lens, i.e. its focal length, but what
is it that is driving it to do so. We definitely know that there is neither a laser beam nor an IR ray that is passing through
our eyes and getting reflected in order to know where the object is, so as to calculate its focal length appropriately. So
I guess it might be using something like contrast maximizing. Why only a look into contrast and why not some other passive
way?
If an image is out of focus it is blur. In a blur image the adjacent colors get mixed, I mean
somewhat averaged so the mean of the absolute difference matrix of the pixels will be less than the value obtained
for a focussed image. The problem of finding the maximum value forms a good feedback system for accommodation to work!
