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Author Topic: How Many Mega-pixels Is My Eye ?  (Read 15457 times)

Offline techmind

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How Many Mega-pixels Is My Eye ?
« Reply #25 on: 20/06/2010 22:26:26 »
I'm absolutely certain this question has been posed and answered on TNS forums before.

Anyhow, a major difference between the image sensor on a typical camera (CCD or CMOS) and the image-sensor in the eye (retina) is that the cameras have uniformly distributed and identical types of pixels over the whole image area -- whereas the retina has a cluster of high-resolution (but poorer sensitivity) colour sensors ("cones") in the central few degrees of vision (known as the fovea), and increasingly sparse and luminance-only (and much more low-light sensitivity) ("rods") in the periphery of vision.


The wonderful brain scans the eye around the image and builds up the detail and fills in (or makes up!) the blanks to make a complete perception of a scene.

So it doesn't make sense to ask what the total "megapixel" count of the human eye is, as you're not comparing like with like.
Also beware that camera-makers are full of sales-hype, and they count each R/G/B subpixel of the imager towards their 'megapixel' total - and then use digital upscaly filtering to deliver an image with that many complete RGB triplets (where we'd normally refer to an RGB triplet as a 'pixel'). In addition to limitations of the lenses, this contributes towards digital camera pictures not being as pixel-sharp as you might otherwise have naively hoped.

That said, the effective resolution of (the central part of the vision of) the eye equates to about 300dpi at a reading distance of about 14inches - if that helps. It comes from an angular resolution, so in millimetres will scale inversely with distance.
« Last Edit: 20/06/2010 22:42:15 by techmind »
 

Offline Geezer

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How Many Mega-pixels Is My Eye ?
« Reply #26 on: 20/06/2010 22:36:58 »
I'm absolutely certain this question has been posed and answered on TNS forums before.


I think you are absolutely right! At least once, but I didn't want to poke Neil in the eye :D

http://www.thenakedscientists.com/forum/index.php?topic=11174.0
 

Offline John Chapman

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How Many Mega-pixels Is My Eye ?
« Reply #27 on: 20/06/2010 23:48:57 »

John has got this bit
"Analogue images are particular, that is they are made out of discrete units. Whereas digital images use a continuous, non-divisable range of values. If you enlarge a digital image it becomes pixelated and granular whereas an analogue image becomes blurry and indistinct."
pretty much totally backwards.


Hi B.C. Yes, you are right, of course. I had it the right way round in my head and I'm not sure why it ended up written that way  ;D.

 

Hang on! The eye is digital.

..... the nerve signals from the eye to the brain are digital. ...Also, there are a finite number of rod and cone cells in the retina that receive the light. These correspond with the pixels in the camera... [etc]


Well you've got me convinced. I have never thought about our vision as being a digital system before but your explaination make perfect sense to me.
 
 

Offline Joe L. Ogan

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How Many Mega-pixels Is My Eye ?
« Reply #28 on: 21/06/2010 00:24:42 »
I am beginning to taste the megacycles in my soup.  Thanks for comments.  Joe L. Ogan
 

Offline Geezer

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How Many Mega-pixels Is My Eye ?
« Reply #29 on: 21/06/2010 00:29:24 »
I am beginning to taste the megacycles in my soup.

Joe: You have to use megahertz these days. It's something to do with the car rental outfit I think.
 

Offline neilep

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How Many Mega-pixels Is My Eye ?
« Reply #30 on: 21/06/2010 00:43:18 »
I'm absolutely certain this question has been posed and answered on TNS forums before.


I think you are absolutely right! At least once, but I didn't want to poke Neil in the eye :D

http://www.thenakedscientists.com/forum/index.php?topic=11174.0


DOH !!..well it was over two and half years ago !....plenty new peeps deserve to read the wondrous text that have been produced as a consequence of it's resurrection !
 

Offline Joe L. Ogan

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How Many Mega-pixels Is My Eye ?
« Reply #31 on: 21/06/2010 23:21:33 »
As I understand it, you may see a pixel but you have no pixels in your eye.  Thanks for comments.  Joe L. Ogan
 

Offline Bored chemist

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« Reply #32 on: 22/06/2010 06:52:09 »
Pixel just means picture element.
In the eye, the picture is made up from elements called rods and cones; the rods and cones are pixels.
 

Offline imatfaal

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« Reply #33 on: 22/06/2010 12:06:55 »
I wonder how long before the ccd of digital cameras is designed with an 'artificial fovea' - by this I mean a concentration of cells/pixels in the centre.  At present much of the ccd 'real estate' is wasted; a 6"x42 / 150mm x 100mm print has half its information in a 11/16" / 17.5mm  band around the edge.  Very few photographs have their subject matter in this area.  A digital zoom to remove a small border, in fact loses half the information. 

If the eventual limit on size of ccds is the file size (which I am not sure of at all) - then I would prefer that the centre of the photo is more information dense to allow for superior digital zooming.  Matthew
 

Offline tommya300

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How Many Mega-pixels Is My Eye ?
« Reply #34 on: 22/06/2010 20:06:44 »
Thank you for making me realize the nerves work in pulses, I was incorrect,
 I do not know what PCM is used for. I do know that PCM contains more information in its waveform than just a modulated pulse. Thank you sincerely for correcting me in several areas you pointed out to me.

Here is something that interested me, I would like to share. It is over my head but it does sound like it isn't over yours.
 
"Computers operate on a single number that is essentially constant from each input pixel. (The computer pixel is basically the equivalent of a biological photoreceptor.) Fourth, the retina performs all these calculations in parallel while the computer operates on each pixel one at a time. There are no repeated summations and shifting as there would be in a computer. Finally, the horizontal and amacrine cells play a significant role in this process but that is not represented here."

I still stick to the idea that there are no pixels to be counted in the eye.

http://en.wikipedia.org/wiki/Retina

See ya
Later friend
NO Ad hominem abusive intended Sincerely

« Last Edit: 22/06/2010 20:20:39 by tommya300 »
 

Offline Bored chemist

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How Many Mega-pixels Is My Eye ?
« Reply #35 on: 22/06/2010 20:26:33 »
"I still stick to the idea that there are no pixels to be counted in the eye."

Please yourself, but there are about 100 million of them.

From the wiki page you cited
"Physical structure of human retina

In adult humans the entire retina is approximately 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods."
 

Offline Geezer

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How Many Mega-pixels Is My Eye ?
« Reply #36 on: 22/06/2010 21:23:13 »
"I still stick to the idea that there are no pixels to be counted in the eye."

Please yourself, but there are about 100 million of them.

From the wiki page you cited
"Physical structure of human retina

In adult humans the entire retina is approximately 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods."

I believe BC is quite correct in saying that the cells on the retina constitute discrete light receptors. The CCDs in digital cameras are also discrete light receptors, so, at that level, there is little difference. It's interesting that the numbers are not so different either.

The camera's optics seems to be a bit better than human optics, but human post processing seems to be greatly superior to any digital camera currently available.
 

Offline tommya300

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How Many Mega-pixels Is My Eye ?
« Reply #37 on: 22/06/2010 21:56:30 »
"I still stick to the idea that there are no pixels to be counted in the eye."

Please yourself, but there are about 100 million of them.

From the wiki page you cited
"Physical structure of human retina

In adult humans the entire retina is approximately 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods."

I believe BC is quite correct in saying that the cells on the retina constitute discrete light receptors. The CCDs in digital cameras are also discrete light receptors, so, at that level, there is little difference. It's interesting that the numbers are not so different either.

The camera's optics seems to be a bit better than human optics, but human post processing seems to be greatly superior to any digital camera currently available.

Yes I agree being put this way. I interpreted that site I had past on, shows the similarity and differences. My copied statement from that site.
Someone please interpret it please, because in different words in some parts I interperate it as coralation with
Techmind:
http://www.thenakedscientists.com/forum/index.php?topic=32278.msg313346#msg313346

The number of light receptors can be counted in the eye.

Pixels in a camera can be counted
 If you decide to call the bio parts that similar in function with the particular computer part and label them as one label, us less educated people will never catch on.
« Last Edit: 22/06/2010 21:59:04 by tommya300 »
 

Offline Geezer

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« Reply #38 on: 22/06/2010 23:20:54 »
If you decide to call the bio parts that similar in function with the particular computer part and label them as one label, us less educated people will never catch on.


I don't think there is any deception. The detectors in the eye and the detectors in a camera's CCD do the same thing. They both react to quanta of electromagnetic energy (aka photons) within a certain frequency range.
 

Offline tommya300

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How Many Mega-pixels Is My Eye ?
« Reply #39 on: 22/06/2010 23:30:10 »
If you decide to call the bio parts that similar in function with the particular computer part and label them as one label, us less educated people will never catch on.



I don't think there is any deception. The detectors in the eye and the detectors in a camera's CCD do the same thing. They both react to quanta of electromagnetic energy (aka photons) within a certain frequency range.

OK I can understand that, but that was never contested not the issue...

can you please tell me this does not apply

 
"Computers operate on a single number that is essentially constant from each input pixel. (The computer pixel is basically the equivalent of a biological photoreceptor.) Fourth, the retina performs all these calculations in parallel while the computer operates on each pixel one at a time. There are no repeated summations and shifting as there would be in a computer. Finally, the horizontal and amacrine cells play a significant role in this process but that is not represented here."
« Last Edit: 22/06/2010 23:32:23 by tommya300 »
 

Offline Bored chemist

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How Many Mega-pixels Is My Eye ?
« Reply #40 on: 23/06/2010 07:00:42 »
It's ironic that one of the first stages of image processing in a camera is the conversion of an analog signal to a digital one. (The charge in each pixel is measured, then quantised).
In the eye, one of the first stages is the conversion of a digital signal to an analog one by summation in the retina.
However, it remains the case that both signals leave the eye or camera as digital ones- albeit processed. The optic nerves are either on and off, and so is the USB port signal (or whatever).
The actions of the retina are signal processing. when you look at a picture these processes happen whether the original picture is digital or analog. This post-procesing does not detract from the fact that the original image is captured by a finite array of individual pixels in both cases.

 

Offline Geezer

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« Reply #41 on: 23/06/2010 09:11:01 »
It's ironic that one of the first stages of image processing in a camera is the conversion of an analog signal to a digital one.

Perhaps not so ironic. It seems that "light" itself may be quantized in the form of photons. Photons seem to have rather digital characteristics.

BTW, I'm not claiming to understand much of this. These are just some of my sporadic thoughts.
 

Offline daveshorts

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How Many Mega-pixels Is My Eye ?
« Reply #42 on: 23/06/2010 09:38:11 »
Something which has been hinted at so far, but I thought I would say explicitly:

One big difference is that a camera has a constant pixel density all over the image, where as your eye has a very high pixel density at the fovea and a much lower one everywhere else. So you see 'what you are looking at' at a much higher resolution (and in better colour) than everything else.

This actually makes the job of making a camera more difficult as when looking at a photo you can move your eyes around, so if the camera tried the same trick as your eyes, you would complain that the edges of the photo looked pixelated or at least out of focus. So the camera manufacturers need to pump out high resolution everywhere with a consequent increase in data that they have to throw around.
 

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How Many Mega-pixels Is My Eye ?
« Reply #42 on: 23/06/2010 09:38:11 »

 

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