Resolution of the human eye
clarkvision.com
clarkvision.com
The first sentence seems to contradict the last. It's obvious that you can't take in a 120 degree view in detail even near to 576 megapixels in any period of time short enough to compare to take one photograph. If we instead consider a rather modest 1.3 megapixel camera, and using the 15 fps figure that's provided elsewhere in the article, it will take 30 seconds to "record" the scene in full detail. Also, that assumes that the scene is intensely diverse - it seems that the brain has a pretty efficient compression algorithm. Looking out at the sea, you can immediately dismiss 80% of the scene as "water" and "sky" and concentrate on the detail, arriving quickly at a very high resolution image for the 20%, even with much less than 1,3 megapixel "per frame" resolution.
According to this article this is 530 ppi (pixel per inch)
Now, if my math is not entirely flawed (please check) for a 27 inch monitor with a 16x9 ratio this would mean a resolution of
12,472 x 7,015
The iPhone 4 has 326 ppi and I just took off my glasses and I really had to focus until my eyes hurt to be able to see a single pixel. (I failed, I couldn't see one) Also I have to get really close on to my PC screen to see single pixels (235 ppi)
Now my question is, how could my retina have 530 ppi if I can not identify single pixels on a 326 ppi device?
Furthermore I fail to understand the most basic assumptions & calculation in this article:
> 53*60/.3 = 10600
Assuming that this calculation is correct and he just left a part out. I have problems understanding the first and most basic assumption:
> Thus, one needs two pixels per line pair, and that means pixel
> spacing of 0.3 arc-minute!
> 0.7 arc-minute, corresponds to the resolution of a spot as non-point source
> Again you need two pixels to say it is not a point
> Again, you need an minimum of 2 pixels to define a cycle
If this point does not hold up, the entire following calculations are way off. I would be thankful if someone could enlighten me.
#Edit: as ristretto stated earlier, there are ~ 100 million cells in the human eye. There are only ~200 000 cells in the fovea. Also everything gets compressed and send through only ~ 1 million nerve cells. Just to be interpreted by 140 million neurons in the V1 area. Short: measuring the megapixel of the human eye is quite a fruitless exercise. The human eye does not work like a homogenous camera/monitor.
The maximum visible pixel per inch (ppi) on the other hand have serious implications to technology and hardware development. Therefor I have much greater interest in this metric.
Assuming your retina does indeed have 530ppi or so (there's no guarantee that all retinas are ideal), there still remains the question of whether your eyes' focusing systems are in good enough shape to produce that resolution, whether any vision flaws are corrected fully by your glasses/contacts, etc.
(edit to add one more correction)
> 53*60/.3 = 10600
? Why did he multiply it times 10? Is this a calculation error, or am I just missing something?
I guarantee you can. Make a nice white image and place a few single pixel black dots on it. You'll see them just fine.
Or, for that matter, dead pixels.
Thus, the mapping of "pixels" to the number of retinal ganglion cells is probably less tenuous than a photoreceptor-to-pixel mapping. Now that I think about it, perhaps an even better definition of a physiological pixel would be a functional measure: the number of distinct, electro-physiologically measured center-surround fields in the thalamus. In that case, the effective megapixel rating of a human visual system is only indirectly related to the sheer numbers of photoreceptors, but more closely related to the wiring pattern. This wiring pattern is much more difficult to experimentally measure than simply counting neurons because it would involve flashing tiny, contrast-y dots of light in front of a fixated mammal while poking an electrode around in the thalamus. [This is outside of my main field, so it may have been done, but I don't know the results.]
Two side notes of interest:
1. Photoreceptors are oriented towards the rear of the retina and are embedded in a dark sheet of cells called the pigment epithelium. The upshot of this is that every photon that is involved in our visual perception has traversed a tangle of bipolar cells, ganglion cells, and their associated axons (it is easy to overlook this fact in diagrams, such as at http://en.wikipedia.org/wiki/Retina , because it is usually only mentioned textually in the figure caption). The fovea is relatively free of these light-scattering objects and, in addition to a higher ratio and density of cone cells, is why primate visual acuity is highest in the fovea.
2. In extremely low light-adapted rod cells, the absorption of single photon can trigger photo-transduction. Thus, our visual system has the capacity to operate at the very limit of physics. If I recall correctly (i.e., no citation on hand), this has even been experimentally demonstrated, although the experiment must have been pretty demanding, what with photon shot noise and all. [This last side note #2 is what I had in mind when I referred normal visual processing in the first paragraph. Even though you might think that this validates the photoreceptor:pixel metaphor, at best a human would probably just report a tiny inkling of a flash in some general vicinity with very poor spatial and temporal resolution.] Ah, I now see ristretto mention that.
Clouding the issue even further is the fact that different areas of central vision processing handle different features. Some areas are tuned to react to points, some to bars, some to grids, some to movement, some to rotation, etc. Perhaps it would be simpler to make the comparison in the other direction: "How intricate do I have to make this visual scene to fully exercise the perceptual abilities of grating-sensitive neurons in the Lateral Geniculate Nucleus of the thalamus." That way, we could put some sort of upper bound on the useful specifications of a pixelated display. We would then have to iterate over all the known feature sensitivities (bars, grids, rotations, etc.).
Display engineers surely must know that below such-and-such pixels per inch, a screen can present any reasonable perceptible pattern. So outside of casual interest, ristretto and I think that eye "megapixels" is relatively meaningless.