The Retina:
The Retina...the center of the eye in more ways than one. Cells in the retina break down what a person sees into thousands of elements such as brightness, color, movement, etc. The job doesn't stop there, however, it also tells the brain these things through electrical signals. This is done very quickly--more quickly than humans can understand even with highly sophisticated help.
Layers of rods and cones receive light, then bipolar cells organize this information and send it to ganglion cells which then send it to the brain via the optic nerve.
In the analogy of the human eye to a camera, the retina would be the film.
Picture from http://www.driesen.com/human_eye.htm