The Human Eye as an Image Sensor
MAURIZIO DI PAOLO EMILIO
In human sight, the eyes, brain and optic nerve are all come into play during the image acquisition process. Cameras were built using the human eye as a model in an attempt to replicate its features.
The eye is composed of various parts. The retina is sensitive to light and is formed by photoreceptors for image conversion. Through the retina the image is broken down into electrical packets and conveyed to the optic nerve. Information is received by the brain at high speed, reaching the diencephalon, where it is processed and matched to the individual's previous knowledge.
Our eyes work with our brain to create the image we perceive: the eyes regulate focus (by bending light through the lens in the eyeball) and translate the photons into an electrical impulse to be processed by the brain.
The cornea is just like a camera lens. The pupil and iris represent the diaphragm. The eyelids are the camera shutter and affect the shutter speed. The crystalline lens is the autofocus. The retina is the real sensor whose dimensions can be comparable to a full-frame of 24x36 mm. The retina is composed of a myriad of pixels. Roger N. Clark calculated a possible number of megapixels under ideal conditions, something like 570 Megapixels.
The focal length of the human eye is between 17 and 24 mm. Our angle of view is 130°, which is reduced to 55° to the focus point. Several studies have stated our eye is a lens with an average shutter speed of around 1/100 second (in healthy individuals).We could say the binomial cornea/pupil corresponds to the binomial frontal lens/mobile lens of the camera: the cornea collects the divergent rays of light and conveys them through the pupil.
The human eye is extremely good at handling images when illuminated by strong light, so it becomes insignificant to talk about "noise" as the human brain simply "completes and corrects" possible problems in sight.