Hiron
Joined: Aug 16, 2007
Posts: 435
From: Denpasar - Bali, Indonesia
PM |
The summary:
How many megapixels?
The average human retina has five million cone cells receptors on it. Since the cones are responsible for colour vision, you might suppose that this equates to a 5 MP equivilant for the human eye.
But there are also a hundred million rods cells receptors that detect monochrome contrast, which plays an important role in the sharpness of the image you see. And even this 105MP is an underestimate because the eye is not a still camera.
You have two eyes and they continually flick around to cover a much larger area than your field of view and the composite image is assembled in the brain - not unlike stitching together a panoramic photo. In good light, you can distinguish two fine lines if they are seperate by at least 0.6 arc-minutes (0.01.Degrees).
This gives an equivilant pixel size of 0.3 arc-minutes. If you take a conservative 120 degrees as your horizontal field of view and 60 degrees in the vertical plane, this translates to ...
MORE THAN 576 megapixels of available image data.
The Sensitivity of the Human Eye (ISO Equivalent)
At low light levels, the human eye integrates up to about 15 seconds. The ISO changes with light level by increasing rhodopsin in the retina. This process takes a half hour our so to complete, and that assumes you haven't been exposed to bright sunlight during the day.
The sensitivity of dark adapted eye to be about ISO 800.
During the day, the eye is much less sensitive, over 600 times less which would put the ISO equivalent at about 1.
The Dynamic Range of the Eye
This is like saying a camera can function over a wide range by adjusting the ISO speed, aperture and exposure time.
In daylight view, the eye can see over a 10,000 : 1 CONTRAST RATIO, but it depends on the scene brightness, with the range decreasing with lower contrast targets. The eye is a contrast detector, not an absolute detector like the sensor in a digital camera, thus the distinction.
The range of the human eye is greater than any film or consumer digital camera.
In low light, the ISO sensivity increased, that leads to increased dynamic range
Here is a simple experiment you can do. Go out with a star chart on a clear night with a full moon. Wait a few minutes for your eyes to adjust. Now find the faintest stars you can detect when the you can see the full moon in your field of view. Try and limit the moon and stars to within about 45 degrees of straight up (the zenith). If you have clear skies away from city lights, you will probably be able to see MAGNITUDE 3 stars. The full moon has a stellar magnitude of -12.5. If you can see magnitude 2.5 stars, the magnitude range you are seeing is 15. Every 5 magnitudes is a factor of 100, so 15 is 100 * 100 * 100 = 1,000,000. Thus, the dynamic range in this relatively low light condition is about 1 million to one, perhaps higher! In LCD TV measures, 1.000.000 : 1 or MORE contrast ratio, about 20 F-STOPS are possible
The Focal Length of the Eye
the correct value is ~22 mm focal length
This then makes more sense for the F/RATIO: with an aperture of 7 mm, the f/ratio = 22.3/7 = 3.2.
Of course these values vary, with cited values from 22 to 24 mm, same with the aperture. The maximum aperture also decreases with age.
The f/stop maximum in the astronomical community is spec'd at f/3.5 for a dark adapted human eye. With a maximum aperture of 7mm, this implies about a 25mm focal length. Astronomical telescope minimum magnification is commonly cited as an f/3.5 light cone, meaning if you look through a faster system, the eye's f/3.5 optics can't gather all the light.
Other Technical Data:
HUMAN EYES DEPTH COLOR: 2-3 Million Colours
Thus means, 16.7 Million Colours Monitor (24-bit) is a waste for us 
- Quick autofocus from distances of 10 cm (young people) ... 50 cm (most people 50 years and older) to infinity. Your eyes are able to focus in less than 100ms or 0.1 seconds, thus is faster than any DSLR on the market.
- Angular resolution: 1–2? (about 0.02°–0.03°), which corresponds to 30–60 cm at a 1 km distance
- Field of view (FOV): simultaneous visual perception in an area of about 130° × 160°
- Faint stars up to +6.5 magnitude
- Photometry (brightness) to ±10% or 1% of intensity —in a range between night and day of 1 : 10,000,000,000
- Symmetries of 10–20? (5–10 cm per 1 km) —see the excellent measurements of Tycho Brahe and the Egyptians
- Interval estimations (for example at a plan on paper) to 3–5%.
- Unconscious recognizing of movement (that is "alarm system" and reflexes)
Visual perception allows a person to gain much information about his or her environment:
- the distances and 3-dimensional position of things and persons,
- the vertical (plumb line) and the slope of plain objects
- luminosities and colours —and its changes by time and direction
- ... and other qualities of objects.
[ This Message was edited by: Hiron on 2008-07-18 10:09 ] |
Posted: 2008-07-18 05:18
