is processed on the retina
of the eyeball
using two different types of receptors
, the rods and cones. Rods measure the brightness
of the light hitting them (black-and-white vision), and cones measure the amount of either red, green, or blue light (color vision).
Resolution of human vision is difficult to quantify because the density of rods and cones changes, independently, across the entire retina.
You have a higher density of cones near the fovea of your retina than around it, but rods are nearly equally distributed throughout the entire retina outside the fovea. The fovea is where vision is sharpest, the center of what you're looking at.
The area considered the "central retina" is a circle 6mm in radius around the fovea, an area of about 113 mm2, and your entire vision is a circle about 21mm in radius, or 1385 mm2. The average human has about 75,000 cones in the fovea of each eye, and comparatively few outside. Rods, however, average about 100,000 per mm2 (400,000 per mm2 at maximum density), which would mean you have about 140 million across your entire retina. Pretty hi-res, that.