Each picture camera that we buy from stores have certain resolution given in Mega Pixels. I want to know what is the human eye resolution in this unit.
Following is an extract from Wikipedia:
Visual acuity is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white — black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white — black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a gray block, is then the measurement of visual acuity of the eye.
For a human eye with excellent acuity, the maximum theoretical resolution would be 50 CPD (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD. A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.
Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair. A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans.
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It's worth adding that some animals (like African vultures for example) have much higher resolution that humans and can see in much greater detail.
It might be possible to get closer to an actual "megapixel count" for the human eye by considering the individual cells in the retina that respond to light, the so-called rods and cones. Each eye apparently contains something like 120 million rod cells, which are not sensitive to colour, and 6 million cone cells, which are.
Since each of these cells has the ability to detect light independently, is it accurate to say that the human eye has a resolution of 126 megapixels (i.e. 126 million pixels)? Probably not. At least for the rods (I'm not sure about the cones), impulses from several cells apparently get combined on their way to the brain, so several "pixels" effectively get merged into one. This must lower the megapixel count dramatically. Also, the brain processes the input from the rod and cone cells in complex ways (picking out visual "edges", for example) that make the process of human vision fundamentally different from anything that happens in a digital camera.
As a vertebrate palaeontologist, I'm already somewhat out of my depth. Can any of my colleagues who know more about physiology take this approach further?
It would be difficult to put a megapixel count on the eye. For one, as Corwin stated, each receptor does not have its own neural receiver. Near the fovea, for the cones, it is a 1:1 relationship, but as one gets farther away with the rods, you get get up to a 1:20 relationship between receptors and nerves (i.e. 20 rods feeding into one neuron). Then all the input from these receptors gets filtered through several layers of cells that pick up only certain aspects of the view. Some cells will pick up only horizontal lines, others only movement, etc. Our eyes do not function at all like cameras. Even after that, the image still needs to be interpreted by the brain, which asembles all these inputs into an image. That image is very patchy because the eye moves rapidly from point to point and it dos not pick up an image in between. Think of the eye as a high speed camera taking several shots a second which the brain then puts together into a panoramic view. The numerous gaps between shots are filled by what the brain expects to be there. This is one of the main ways that magicians fool people is by playing to those expectations and then secretly changing them.
Because the eye and the brain work so fundamentally different, I can't see a justifiable way of comparing them in terms of megapixels.
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