# 3d image ?

Discussion in 'Physics' started by Mathematics!, Jun 11, 2010.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
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OK, I know that an image is created by the reflection of light back to your eyes. And I know the color for a part of an image is given by the frequency or wavelength of light being reflected back to your eye.

But what gives it the 3D (non flat look) i.e what gives an image it's depth.
If it is the distance at which light reaches your eye then how does your body keep track of what light source is farther or closer away?

Somebody told me it has to do with polarization. But I don't really understand how this can differentiate it.

Thanks for any help.

2. ### CVMichael Senior Member

Aug 3, 2007
416
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Amm... unless I'm totally missing the point here, I always thought that we see in 3D because we have 2 eyes...

Another part is that our brain makes things in 3D in our mind from experience. So this means that even a person with one eye can still see in 3D because our brain will process the image and "places" each object in space from what it learned previously.

For example, we know that a table is rectangle shaped, so when we look at an image we can tell that it is a table (from color, things that is on it, legs, etc.), and we can place it in space (in our mind) from the contours, knowing already it's shape from experience.

3. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4

But then if I close one eye the only reason I can see in 3D is that my brain/mind remembers what 2 eye's displayed the image like and try's to reproduce it.

So people that where only born with one working eye would always see in 2D?

I just think their is more to it then this.

questions
1) how from having 2 eyes does it work...I mean does the 2 eyes act like some type of triangulation thing to find the distance the object should be placed...etc

2) How does 3D movies make it look 3D. Basically they tell you to put on these special glass , what are these glasses doing to make it look 3D?

4. ### CVMichael Senior Member

Aug 3, 2007
416
17
Actually they still see in 3D... from experience.

For example, (for someone with one eye) when you are a child, you see the object, you don't know where it is, then you put your hand out, and you try to reach it, first of all you see your own hand, and you know where it is as you can feel it, but as you get closer to the object, you can see how all the angles change while you move, then you finally touch it, and now you know that when it looks "this" big, and when it has "these" angles, then it's "that" far...

So next time you see it, you again compare all the angles, and see the image size, so the brain now knows approximately how far it is.

Also, one thing that I did not mention before (forgot), is that while you move, using your memory, you remember how it was before, and now you see how it looks now... it's basically like having 2 eyes, except the other eye is your memory.

For example, I remember once I made a program on the computer to display a cube by drawing the edges (lines from each point). The cube did not move, and it was showing on the monitor in 2D, I was confused because I did not see the cube in 3D (in my mind), then I changed the program to rotate it, and immediately I started to see it in 3D...

So, motion is a big thing too.

Exactly... triangulation...

There are a few types of glasses, but for example, (I know this for a fact), I used to have a video card that came with 3D glasses (with wire that plug into the video card). The "glass" is basically like the display of a digital hand watch, the color is black when it receives electricity, or transparent when it does not.

The monitor had to be set at double the frequency, 120Hz, and the video card is flipping back and forth between 2 images that were taken a little bit off from the other (like 2 eyes), and the glasses were turning off/on each eye taking turns, so only one eye can see at any one time, and it was going at the same frequency as the monitor.

So, in the end, one eye sees one of the pictures, and the other eye sees the other picture, therefore it appears 3D, as if it's coming out of the screen.

By the way, the new 3D televisions do the same thing, double the frequency, 2 images, and glasses that turn off one eye at one time, except that the glasses are wireless...

5. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok , I kind of get it. But that is alot of info your brain/mind has to interpret in
a split second...etc all the time for imaging. Sort of amazing!

Anyway
Would closing one of your eyes while watching a 3D movie with the glasses kill the 3D of it. You would be only getting one of the 2 frames.

Unless something like memory paging is used to store the other image in memory to compare...etc like the person that was born with one eye...?

Also this is probably an unsolved problem but I will ask it anyway to see where it stands
From this I am wondering how the mind/brain keeps track of all this stuff ...is their sort of an algorithmic way it does it.
If you where sampling stuff using IR imaging... do we have the ability to sample/display in 3D... if so we must have built the equivalent of the transmitter/reciever (eye's and light) but for IR... if so then how do we do 3D for this. We must at least know of an algorithmic way of doing this and it wouldn't be far fetch to thing that the human eye's are doing something equivalent.

Some people have depth perception problems and are excluded from flight school because of this.
Maybe if we did the equivalent for the human eyes as we can for 3D IR imaging we could fix these eye problems?

By what you are telling me depth perception problems would be cause by the inability to triangulate correctly or use the mind to store previous imaging,...etc (this is more fundamental then a color perception problem which is only cause by cones /rods not working in the eye )

Last edited: Jun 11, 2010
6. ### Wendy Moderator

Mar 24, 2008
20,772
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There is a second mechanism for 3D, focus. The eye has a interesting layer of nerve cells behind the retina to preprocess the images the eye sees. It is thin, but as intricate as brain tissue.

Apr 20, 2004
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8. ### dokworm New Member

Oct 1, 2010
5
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Yes, closing one eye in a 3D movie collapses the depth back to 2D.

Try this experiment:
You will need an eyepatch, (or be able to close one eye) and a ball.
Have a friend throw you a ball for you to catch one handed. Have them throw it a few times until you can catch it fairly easily. Vary the depth of the throw by a few centimetres each time so you have to reach slightly forwards or backwards to catch it.
Now close one eye (the person catching, not the person throwing) and try to catch the ball with one eye closed.
You will find catching the ball very difficult as your main depth cue has now disappeared.

For 3D movies, they use one of three techniques, but they all have two image streams, one for the left eye and one for the right eye.

The new 3D TVs use LCD shutter glasses. The glasses can darken the left eye and the right eye view in turn. The television displays the right eye image and then the left eye image in sync with the glasses so each eye only sees its image stream.

Originally (usually) the two streams were shot with two cameras side by side, just like the way you would see it in real life with your eyes, so your brain merges them into a single 3D image, the same way it normally does.

Some cinemas use a polarised system, and passive polarised glasses, the left image is polarised in one direction, the right image in the other. The glasses have a matching polarised lens for each eye, so once again you only see the image intended for the left eye or the right eye.

The brain has other depth cues, but the binocular vision cues are the strongest and work well enough to give the illusion of 3D on a TV or in the cinema.

Jul 7, 2009
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Depth perception is an interesting topic and gives you some indication of the power of the visual processing portion of brains. Personally, when I analyze things, I find that stereoscopic vision and parallax play a big role. If you've ever had an injured eye where you have to have your eye covered, you'll surprise yourself a bit and find that you can get around (work and drive) pretty well -- you accommodate pretty quickly. One of the key factors in everyday life is that you have lots of experience with objects and know approximately how big they are; you use this to mentally estimate their distance.

I remember reading the Morse & Feshbach book on theoretical physics in the 1960's and was taken by the stereo pair images in the book of various coordinate systems. The book promised you that if you practiced a bit, you could "optically decouple" enough to merge the stereo images in your mind without using a stereo viewer. This is quite cool.

A few decades later, I got to play with Borland's Turbo Pascal and wrote a program to put a stereo pair for a cube on the screen and rotated it when the arrow keys were pressed. This was a lot of fun, although the computers really weren't fast enough for much more than that. With modern tools and hardware, you can write some impressive simulations.

10. ### DonQ Active Member

May 6, 2009
320
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http://en.wikipedia.org/wiki/Autostereogram

It's a little tricky, but when you finally see the 3D image, you will really be amazed at the image processing power of the brain.

Or go straight to a larger version of the Autostereogram here

Autostereogram

Note: You will not ever be able to see the 3D image with only one eye.

11. ### Wendy Moderator

Mar 24, 2008
20,772
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The ability is reduced, but you are discounting the ability of the eye's focus and brains processing power to measure distance. Even modern computers/software can use this technique, and do for 3D modeling. I suspect you are oversimplifying the problem.

Of course, I'm not talking autostereogram. Took me forever to get it down as far as getting my eyes to cooperate, now I can do it routinely.

12. ### beenthere Retired Moderator

Apr 20, 2004
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Here's a weirdy - the Windows wallpaper called greenstone is an autostereogram. It has no hidden figure, but if you do the crossed eyes thing to see the depth, then your icons float above it.

13. ### DonQ Active Member

May 6, 2009
320
11
I have plastic lens inserts, but I can still see 3D just fine.

A lot of this discussion depends on your working definition of 3D. If I only had one eye and no ability to focus my lens, I could tell which was closer and which was further by moving around a bit, but I would not call this '3D'. In the same way, I would not call a photograph taken with close things in focus, and far things out of focus, '3D'. You can use perspective to tell distance from basic photos, but they also are not '3D'. And simply remembering what is closer gets really really far away from '3D'.

At the other extreme, everything in the universe is (at least) 3D, and that doesn't change with our ability to sense it.

I think that the most useful definition of 3D is the binocular, brain-processed version those with 'normal' vision have, independent of perspective or focus (perspective and focus already have their own names). Ways of simulating this ability count also, but rely on providing slightly offset images to each eye, in anticipation of the way the eyes and brain are going to process it.

I can imagine a computer generated pair of images, with the focus and perspective manipulated so that it does not match the angular shift between images, delivered to each of my eyes. I would be willing to bet that the brain would interpret and believe the distances based on the binocular information, and the focus and perspective would look 'wrong'.

I have experimented with reversing the two images of a 3D set. I have 'seen' people recessed into walls, and portions of exterior trees protruding into a room through a window. Sometimes, the image just can't be 'locked' on (kind of like the autostereogram, blinking in and out). I've also done this same effect with a short periscope, reversing the relative positions of my right and left eye, getting the same effect in real-time. In this case, moving around a little completely destroys the effect. Apparently, if there is enough additional information, including focus, perspective and relative motion, even binocular 3D can be outvoted.

14. ### Amr hamzawy New Member

Oct 6, 2010
1
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really !! it's amazing

15. ### retched AAC Fanatic!

Dec 5, 2009
5,201
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To and fro
Up and down
Left to right

Those are the 3 dimentions regarded as "3D"

Vision is not the only way to experience 3D.

Audio has used 3D for decades.

And surround sound has attempted a 4Dish method of "behind you"

Quadraphonic or "surround sound (4.0)" uses the same timing differences as visual 3D.

Stereoscopic microscopes are 2 - eyed scopes that allow for depth to be perceived.

16. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I use them every day for my job with microelectronics. The machines with vision and pattern recognition use focus to determine distance to the substrate, a pretty standard feature.

Dec 5, 2009
5,201
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show off.