Resolution and human eye

[Intelman07]

Now I am sure the human eye doesn't use pixels in all but what would be the equivelent resolution to match the human eye? Otherwise what "resoultion" does the human eye see at ?

 

[Moohooya]

http://www.stlukeseye.com/anatomy/Retina.asp
6 million cones, 125 million rods.

 

[SuperTool]

Yes, but is there a nerve from each rod/cone to the brain, or are some rods/cones sharing one nerve

 

[amnesiac]

That's a tricky question, because of how intricate the nerology of the eye is.
The cones are mostly at the center and concentrate on colors, while the rods are mostly for peripheral vision and motion detection.

The human eye has 136 million receptors, or a rough density of 160,000 per square millimeter, on average.
However, this does not equate to a 136 megapixel resolution, as there are several rods per ganglion, while cones tend to be at a 1:1 ratio to ganglia.

So... I can't really give you a set answer, but know it's less than 136 megapixels.. probably a good deal less than 100 as well.

(Man, I *love* my bio-neuroscience course now, I feel so smart! )

 

[CTho9305]

Originally posted by: amnesiac 2.0
That's a tricky question, because of how intricate the nerology of the eye is.
The cones are mostly at the center and concentrate on colors, while the rods are mostly for peripheral vision and motion detection.

The human eye has 136 million receptors, or a rough density of 160,000 per square millimeter, on average.
However, this does not equate to a 136 megapixel resolution, as there are several rods per ganglion, while cones tend to be at a 1:1 ratio to ganglia.

So... I can't really give you a set answer, but know it's less than 136 megapixels.. probably a good deal less than 100 as well.

(Man, I *love* my bio-neuroscience course now, I feel so smart! )

In addition, eyes see different colors at different resolutions - specifically, we see blue at a much lower resolution than red/green

 

[Mark R]

At the fovea, the site of the retina responsible for central vision - one cone subtends approx 20-30 arcminutes. Red and green cones outnumber blue cones by approx 100:1.

Nearer the peripheries, the cones are less densely packed, and there are more blue cones.

You can't directly related one cone to one 'pixel' - as there is considerable image processing within the retina, including the pooling of signals from neighbouring receptors to increase sensitivity (at the expense of resolution) and lateral inhibition (edge sharpening). Although at the fovea it can be approximated that there is one outgoing nerve fibre for each cone photoreceptor, in the peripheries there are certainly fewer outgoing fibres than receptors - especially for rods.

Other interesting facts - at about 60 cm (typical reading distance, or for people on this board, distance from a computer screen), 1 cm is approximately equal to 1 degree, in which distance the eye could potentially resolve 150 or so seperate points, in the centre of vision.

 

[Placer14]

I am incredibly impressed. I love this stuff. What is the maximum number of different various of color can the human detect?

 

[anxman69]

Ok, to sum up your question, there is a physical limit to the amount of "pixels" that the human eye can resolve. It has to do with the wavelength of light and the field of view of your eye.

I don't recall off the top of my head what the number is for the eye, however, to make a near-perfect 35MM picture, you would need about 11MP. Once I dig up the correct statistic from my optics book, I'll let you know the exact number.

As for the "number of colors" that the human eye can resolve, it has to do with the visible spectrum of light for a human, which is between 400nm and 700nm (blue to red) or so.

You heard it from an optical engineer.

-Ankur

 

[Mark R]

There is no limit to the number of different shades percievable - the eye and its processing are essentially a fully analogue process - there is no limit below which a difference will be ignored by the processing. However, where contrast is limited (e.g. a computer screen, then then 8bit per channel colour, quite well approximates the minimum perceivable change in brightness).

Where the eye is exceptionally good is in dynamic range - digital cameras have a feeble dynamic range - the brightest object they can resolve is barely 1000x brighter than the darkest that they can resolve at the same time. Film cameras are slightly better. The eye has a range of 10000x or more in the same scene, and over 1,000,000x from maximum dark adapted sensitivity to sensitivity in extremely bright light.

The eye is limited in the range of colours that it can see - while green is most useful to the eye, for assessing shape of objects - the eye actually lacks the ability to perceive a pure green; this is because of the wavelength sensitivity of the cones. The sensitivity spectrum of the red, actually overlaps with the blue, let alone the green - this means that there is no wavelength or colour of light that is capable of triggering green cones only - hence colour resolution in this range is lost.

The limits to pixel resolution in the eye (and indeed any camera) are diffraction, spherical aberration, chromatic aberration and sensor spacing. Under most conditions the eye is not significantly diffraction limited - diffraction limit is approx 6 arc minutes under moderate lighting conditions - this is degraded slightly under high light conditions. Spherical aberration in a healthy eye is quite cleverly cancelled due to opposite aberrations in the cornea and lens. Chromatic aberration is generally very good in red and green, but less good in blue (one reason why there would be little benefit in having more blue cones. It becomes quite poor in the violet region (one reason by UV 'black' lights appear to have a wide purple halo around them).

 

[Rand]

Very interesting thread.
Another question, I've always hear women can see more colors then men... is this true, and if so why?
Does eyesight in men and women vary in any other respect?

 

[Mark R]

I've never heard that there is any difference in colour perception between the sexes - however, 'colour blindness' is considerably more common in males:

The most frequent genetic defects are in the pigments for long and medium wavelength cones (red and green) - resulting in one of the cone types having a defective pigment which may have different optical properties. This gene is X-linked (carried on the X chromosome) - males have one, if that copy is defective, then no functional pigment produced. Females have 2 X chromosomes, which means that they need to inherit 2 defective copies (one from each parent) in order for the defect to be apparent. As there are multiple genetic defects, there are a variety of different types of colourblindness.

 

[glugglug]

Other interesting facts - at about 60 cm (typical reading distance, or for people on this board, distance from a computer screen), 1 cm is approximately equal to 1 degree, in which distance the eye could potentially resolve 150 or so seperate points, in the centre of vision.

150pixels/cm = 0.0666mm dot pitch.

Professional grade computer monitor ~= 0.22mm dot pitch

So between 3 and 4x better resolution in each direction than a really good monitor, at normal viewing distance.

Personally I have a hard time believing it's that low, I would think at least an order of magnitude better.
But then again most people think I'm crazy when they see what resolutions I use, and are pretty shocked when I can read my 2200x1600 19" screen from behind several other people a good 10 feet away (normal small fonts). Typical resolutions most people use, like 1280x1024 on a 17" monitor, I can read from about 40 feet away.

 

[Shalmanese]

As an experimental test, my LCD has a resolution of 1400x1050 and a screen width of 15" (diagonal) so I would have a 12" horizontal and 9" vertical screen. That corresponds to ~117 pixels per inch or 46 pixels per centimeter. If I go into MS paint and place a single pixel in the center of my screen, I get ~ 117cm away before the pixel disappears. Working that out, I get one pixel subtending approximately 6 1/2 arc minutes. However, when I take my glasses off, I only manage about 85 cm which works out to be ~ 9 arc minutes. Try it yourself, YMMV

 

[Gunnar]

I think another you should note is that the human eye is also not constant in its supposed "resolution". The viewing efficiency of the eye drops dramatically when in motion, which is why TV can get away with having an amazingly low resolution (that is in addition to the fact that the average TV sits roughly 12 feet away).

Another astonishing fact is that the eye has an amazing small area of high quality perception. As everyone probably knows, the eye has FAR more rods that cones, and the cones are tightly packed into the area onto which the lens focuses (called the fovea). This tight packaging gives great perception of detail, but it essentially means that a person can only really see about a thumb's worth of area at arms length in the field of vision with any great detail. You can see this for yourself by trying to read a book out of the corner of your eye instead of focusing on it (its very blurry).

But thats not the end of it, otherwise the eye would be worthless. The eye is constantly moving so that this high density patch surveys as much of the field of vision as possible. These muscle movements are called siccades (check spelling), and you will see these if you were to observe any person's eyes closely, it seems almost spasmodic.

In terms of resolution of the eye, its highly dependent on a number of factors, including lighting, contrast, and color. Since night vision is composed entirely of rods, color perception becomes nothing, and the fovea becomes as blurry as any other portion of the eye, hence more light means more distinction. However, too much light leads to the same problem, as the cones have different frequency responses to each wavelength of light. Contrast is another problem, especially since the eye has no upper limit in differentiating between sinusoidal gratings (white and black alternating bars) provided the pattern is bright enough. Lastly, I think everyone knows that the eye is more sensitive to shades of green that to red or blue.

A lot of info, I took a perception class a couple of semesters ago, good stuff. I think someone mentioned the eye is an analog device, which is why its limits are fuzzy.

And women can have better vision than men. Their extra chromosome allows for a genetic mutation is which they have another cone that has another frequency response. Sort of like an X-woman, but not exactly....

 

[Woodchuck2000]

Fascinating thread guys...

The most frequent genetic defects are in the pigments for long and medium wavelength cones (red and green) - resulting in one of the cone types having a defective pigment which may have different optical properties

Does that have any implications for the effective resolution of a colour-blind person's eyes?

 

[kylebisme]

Originally posted by: Mark R
There is no limit to the number of different shades percievable

there is a lot of quantum physicists that would disagree with you on that, not becuse they nessacarly know much about eyes but becuse that belief goes against the basic pricaple behind their science. assumeing the there is a smallest unit in this universe, and knowing that there is most defenatly a visable spectrum, there is only a desccet number of visable shades. just figured i would point that out as i often hear people speaking of analog as if it is fact, when it is actualy a debatable concept with a resonable possablity that it is false. as for the orignal topic, i dont realy know much about it, however its an interesting topic and im glad some of you have good facts to share.

 

[JackMDS]

There are few variables that make it hard to explain the eye as functions to CCD.

The ?refresh? of the pixels is slow (no tweaked nVidia drivers for the brain); it is pending on the Neurochemistry of the nerves.

The refresh rate varies between different types of ?Pixels? (nerve receptors).