Saturday, September 26, 2015

How 3-D Glasses Work

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How 3-D Glasses Work
Multiple Responses:
1.
Although the 1950s are most often considered the 3-D movie decade, the first feature length 3-D film, "The Power of Love," was made in 1922. Since that time the use of 3-D technology in theaters and on television has drifted in and out of mainstream popularity. But, whether you've used them for the big screen or at home in front of your television, you have to admit 3-D glasses are incredibly cool.

They make the movie or television show you're watching look like a 3-D scene that's happening right in front of you. With objects flying off the screen and careening in your direction, and creepy characters reaching out to grab you, wearing 3-D glasses makes you feel like you're a part of the action - not just someone sitting there watching a movie. Considering they have such high entertainment value, you'll be surprised at how amazingly simple 3-D glasses are.

In this article, we'll take a look at the two most popular types of 3-D glasses in use today. But first, let's take a look at something called binocular vision.

Binocular Vision
Most human beings come equipped with two eyes and an absolutely amazing binocular vision system. For objects up to about 20 feet (6 to 7 meters) away, the binocular vision system lets us easily tell with good accuracy how far away an object is. For example, if there are multiple objects in our field of view, we can automatically tell which ones are farther and which are nearer, and how far away they are. If you look at the world with one eye closed, you can still perceive distance, but your accuracy decreases and you have to rely on visual cues, which is slower.

To see how much of a difference the binocular vision system makes, have a friend throw you a ball and try to catch it while keeping one eye closed. Also try it in a fairly dark room or at night, where the difference is even more noticeable. It is much harder to catch a ball with only one eye open than with two eyes open. If you want to try a quick test of your binocular vision, visit this Web site.

The binocular vision system relies on the fact that our two eyes are spaced about 2 inches (5 centimeters) apart. Therefore, each eye sees the world from a slightly different perspective, and the binocular vision system in your brain uses the difference to calculate distance. Your brain has the ability to correlate the images it sees in its two eyes even though they are slightly different.

If you've ever used a View-Master or a stereoscopic viewer, you have seen your binocular vision system in action. In a View-Master, each eye is presented with an image. Two cameras photograph the same image from slightly different positions to create these images. Your eyes can correlate these images automatically because each eye sees only one of the images.

3-D Viewing
In a movie theater, the reason why you wear 3-D glasses is to feed different images into your eyes just like a View-Master does. The screen actually displays two images, and the glasses cause one of the images to enter one eye and the other to enter the other eye. There are two common systems for doing this:

Red/Green or Red/Blue
Although the red/green or red/blue system is now mainly used for television 3-D effects, and was used in many older 3-D movies. In this system, two images are displayed on the screen, one in red and the other in blue (or green). The filters on the glasses allow only one image to enter each eye, and your brain does the rest. You cannot really have a color movie when you are using color to provide the separation, so the image quality is not nearly as good as with the polarized system.

Polarization
At Disney World, Universal Studios and other 3-D venues, the preferred method uses polarized lenses because they allow color viewing. Two synchronized projectors project two respective views onto the screen, each with a different polarization. The glasses allow only one of the images into each eye because they contain lenses with different polarization.
How 3-D Glasses Work
The polarized glasses allow only one of the images into each eye because each lens has a different polarization.

There are some more complicated systems as well, but because they are expensive they are not as widely used. For example, in one system, a TVscreen displays the two images alternating one right after the other. Special LCD glasses block the view of one eye and then the other in rapid succession. This system allows color viewing on a normal TV, but requires you to buy special equipment.
How 3-D Glasses Work
3-D glasses with red/blue lenses

2.
How Do 3D Glasses Work?
3D Stereoscopic glasses are nothing new. In fact you had them when you were a kid and probably didn't even know it. Remember the ViewMaster™ that showed all the cool Disney characters in full 3d? The ViewMaster™ allowed you to look at two pictures of the same thing taken from a slightly different view point and tricked your brain into seeing one 3d image.

In order to see things in 3D each eye must see a slightly different picture. This is done in the real world by your eyes being spaced apart so each eye has its own slightly different view. The brain then puts the two pictures together to form one 3D image that has depth to it.

Still want to know how do 3D glasses work? Keep reading!

Anaglyphic [ana·glyph·ic /"a-n&-'gli-fik/] adjective -- A stereoscopic motion or still picture in which the right component of a composite image usually red in color is superposed on the left component in a contrasting color to produce a three-dimensional effect when viewed through correspondingly colored filters in the form of spectacles.

The mode of 3D presentation you are most familiar with are the paper glasses with red and blue lenses. The technology behind 3D, or stereoscopic, movies is actually pretty simple. They simply recreate the way humans see normally.

Since your eyes are about two inches apart, they see the same picture from slightly different angles. Your brain then correlates these two images in order to gauge distance. This is called binocular vision - ViewMasters™ and binoculars mimic this process by presenting each eye with a slightly different image.

Now you're learning! Need to know more about how do 3D glasses work? Read on. The binocular vision system relies on the fact that our two eyes are spaced about 2 inches (5 centimeters) apart. Therefore, each eye sees the world from a slightly different perspective, and the binocular vision system in your brain uses the difference to calculate distance. Your brain has the ability to correlate the images it sees in its two eyes even though they are slightly different.

If you've ever used a ViewMaster™ or a stereoscopic viewer, you have seen your binocular vision system in action. In a View-Master, each eye is presented with an image. Two cameras photograph the same image from slightly different positions to create these images. Your eyes can correlate these images automatically because each eye sees only one of the images.

A 3D film viewed without glasses is a very strange sight and may appear to be out of focus, fuzzy or out of register. The same scene is projected simultaneously from two different angles in two different colors, red and cyan (or blue or green). Here's where those cool glasses come in -- the colored filters separate the two different images so each image only enters one eye. Your brain puts the two pictures back together and now you're dodging a flying meteor!

3D glasses make the movie or television show you're watching look like a 3-D scene that's happening right in front of you. With objects flying off the screen and careening in your direction, and creepy characters reaching out to grab you, wearing 3-D glasses makes you feel like you're a part of the action - not just someone sitting there watching a movie. Considering they have such high entertainment value, you'll be surprised at how amazingly simple 3-D glasses are.

The binocular vision system relies on the fact that our two eyes are spaced about 2 inches (5 centimeters) apart. Therefore, each eye sees the world from a slightly different perspective, and the binocular vision system in your brain uses the difference to calculate distance. Your brain has the ability to correlate the images it sees in its two eyes even though they are slightly different.

If you've ever used a View-Master or a stereoscopic viewer, you have seen your binocular vision system in action. In a View-Master, each eye is presented with an image. Two cameras photograph the same image from slightly different positions to create these images. Your eyes can correlate these images automatically because each eye sees only one of the images.

The reason why you wear 3-D glasses in a movie theater is to feed different images into your eyes just like a View-Master does. The screen actually displays two images, and the glasses cause one of the images to enter one eye and the other to enter the other eye. There are two common systems for doing this:

Although the red/green or red/blue system is now mainly used for television 3-D effects, and was used in many older 3-D movies. In this system, two images are displayed on the screen, one in red and the other in blue (or green). The filters on the glasses allow only one image to enter each eye, and your brain does the rest. You cannot really have a color movie when you are using color to provide the separation, so the image quality is not nearly as good as with the polarized system.

At Disney World, Universal Studios and other 3-D venues, the preferred method uses polarized lenses because they allow color viewing. Two synchronized projectors project two respective views onto the screen, each with a different polarization. The glasses allow only one of the images into each eye because they contain lenses with different polarization.

3.
Stereoscopy—the illusion of depth created by showing a separate image to each eye—is at least as old as photography itself. In the last few years, however, stereoscopic 3D movies have come back in a big way. Theaters show you 3D movies by projecting two images on one screen and giving you specialized glasses that separate the images. But how do those glasses work?

POLAR OPPOSITES
There are several competing 3D technologies, but the most prevalent one in theaters today is based on polarized light. The technology that fueled the 1950s 3D boom, which is still in use today, is linearly polarized stereoscopy. Two images are projected through polarizers of two different orientations, typically 45 and 135 degrees relative to the horizon. The projected images are then filtered using polarizer films in the lenses of your glasses en route to your eyes. In this way, one image is excluded from your left eye while the other image is excluded from your right.

In the original formulation of this system, two projectors were used, and projectionists needed to take great care to make sure the two images were well aligned, perfectly synchronized, and equally bright. This problem has been eliminated with the rise of digital projectors. One of the other major problems, though, is inherent to the linearly polarized system: It requires the glasses to be parallel to the projector screen in order to prevent the images from leaking through their respective 'dark' lenses. This means that if you bend down to grab the popcorn, or turn to whisper to your friend, or if you sit off to the side of the theater instead of in the center, then the 3D effect will be compromised and you may get a bit of a headache.

The latter problem is corrected with circularly polarized 3D, patented in 1989. This is the method used by the RealD system, the most widely used system in theaters today. Here, one of the images is projected using light waves that trace out a left-handed spiral, and the other using light that traces out a right-handed spiral. Each lens contains a quarter wave plate, which is a passive device that transforms the two counter spiraling waves into two perpendicular linear waves. Then the familiar linear polarizers cut out one image from your left eye and the other image from your right.

So how do you know what kind of 3D glasses you're wearing? Slip into the bathroom during the movie and look in the mirror with one eye closed. The handedness of circularly polarized light is reversed when it reflects off a mirror, but the orientation of linearly polarized light is preserved. So, if the lens in front of your open eye is blacked out, then you are wearing circularly polarized glasses. If the lens in front of your closed eye is blacked out, then you are wearing linearly polarized glasses (or possibly active shutter 3D glasses—a topic for another post).

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