how do 3D movies work, and why are the glasses 2 colors?
In: Technology
3D movies (and books) work by having two layers of information encoded on the screen/page. You then wear a special pair of glasses that filters out one layer so that your left eye only receives on layer of information and your right eye receives a different layer. This is basically how your eyes work in real life since they are spaced out from each other (they each have a different point of view of the world). By mimicking how your eyes work in real life, you can create the illusion of three dimensions.
Early on, it was common to do this with colors. You would have a layer with one image in red and another layer with one image in blue. You would then have glasses with a red lens (which filters out the red layer) and a blue lens (which filters out the blue layer).
Today, we work with light of different polarization. Light that hits your eyes can be though of as a wave. Think about if you and a friend took a jump rope and one of you wave your arm up and down making the rope undulate, creating a wave starting from your end and moving toward your friend. You can do this in an up-and-down fashion, or a left-to-right fashion, or any orientation in between. We call this orientation *polarization.* Light waves behave in this same fashion and individual waves will be oriented randomly.
We can create filters which will block light waves that are oriented in a certain way. This is how sunglasses work. For a 3D movie, we can create an image with two layers of information and each layer only uses light of a given orientation. Imagine one layer only uses light oriented up/down and the second layer only uses light oriented left/right. Then your will have one lens which blocks on type of polarization and another lens that blocks the other. The result is the same with the red/blue strategy above, but now you can do it using any color and create a more realistic image.
There’s different types of 3D but they generally all work the same way. In short, the lens over your left eye only lets certain images pass through to that eye, and the lens over your right eye does the same, but with a different image.
The eye sees in 3D because they are offset and each receive a slightly different image fused by the brain to be able to see in 3D. Flat screens mostly interfere with this process because they only display a single image that is seen virtually identically by both eyes. 3D movies are typically filmed with two cameras offset so they capture two different images of the same content. They then display these images in a way that 3D glasses enable splitting those separate images into each eye separately.
In the case of red/blue like you mentioned, one of the cameras films with a red filter, the other films with a blue. When both are displayed on the same screen and you’re wearing red/blue glasses, one eye sees only the red content, and the other eye sees only the blue content. The brain fuses these images together and makes it look 3D.
Newer 3D technology allows us to do this without distorting the color by using polarized lenses (passive) or by blocking the frame not intended for each eye with electrically activated shutters so each eye only sees the frame intended for it (active).
Stare out your window. Cover up one eye, then the other eye, back and forth. Notice how when you switch eyes, the far away objects barely change, but the ones close to your eye jump around a lot? That’s called parallax! When you have both eyes open, your brain can figure out how far away stuff is by subconsciously comparing the differences between what your left eye and right eye are reporting.
To make a 3D movie, we need to TRICK your brain into thinking that it’s seeing parallax, when really we’re just using a flat screen like a normal movie. There’s a few different ways to do that trick. The one with the 2-colored glasses works by making your left eye and right eye each see different parts of the movie. If you take off the glasses, the screen will look blurry, but it’s blurry in a very peculiar way. Everything will look like it’s bleeding red color to the left and bleeding blue color to the right (or vice versa). The more that the colors bleed away from the center, the more difference that your eyes will detect when you put the glasses back on — and your brain will be tricked into thinking that the differences it’s seeing are real parallax.
To make a movie appear 3D, there needs to be a different picture shown to each eye. Older movies did this with the red/blue tinted glasses. The movie shown on screen would contain two pictures at once – one would be filtered out by the blue lens, and one by the red, so each eye only sees the picture it needs to.
Modern 3D movies do the same thing but with polarized lenses. One only lets through light polarized vertically, and one horizontally.
3D movies work by projecting different images into your eyes so that your left eye see a different perspective from the right eye, just like in the real world. There are several different technologies used for this. What you are refering to is an older technique that uses color to split one image into two. So you have a normal screen or projector but show the red light from one camera and the green light from the other camera. The audience is then given tinted glasses that filters away the light of the other image. A more modern approach is to use a special projector or screen that is capable of showing two images at different polarizations. The viewer then uses glasses with polarization filters in the different orientations to filter the light. The advantage of this is that each eye gets the full color spectrum however it requires specialized equipment. Another approach is to use a lenticular lense on the screen so that each pixel is only projected into a sector of the view field. So you will only be able to see every second pixel, however moving to the side you will only see the other pixels. By positioning yourself at exactly the right angle from the screen you are able to have your eyes see different pixels without any glasses. This is a relatively cheap approach however it is only usable by one person and he have so sit perfectly still.
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