I remember as a kid when I went to a 3D movie and you would have to wear those glasses with one blue eye and one red. Then a couple years later, you don’t need those red/blue glasses but these clear ones. And now you don’t need glasses at all.
Why is that?
In: 9
So the red/blue or red/green method essentially made your two eyes see different images that your brain then merged together to give the illusion of three dimensional image. This works because the image being projected has a red image and one has a blue (or green, less popular) offset. The red lens blocks the ~~red~~ blue light and the blue/green lens blocks the other set of light and this is how it makes each eye see a different image.
The trouble with using color to make each eye see a different image is that it significantly impacts the color of the image you’re seeing. So, they produced the “clear” method that uses polarized lenses to get the same effect.
I say “clear” because it’s actually colored yellow and brown. With the polarized method there are two images projected, one polarized horizontal, one polarized vertical and the glass’s lenses each blocks light of a vertical and horizontal polarization respectively giving the illusion of three dimensions with a much lower impact to color quality.
[https://entertainment.howstuffworks.com/why-arent-3d-glasses-red-and-blue.htm](https://entertainment.howstuffworks.com/why-arent-3d-glasses-red-and-blue.htm)
There are better ways now of feeding the appropriate image to separate eyes than red/blue lenses and thus can preserve colour in the images. One uses up/down versus left/right polarization. Another, suited to digital media, is to synch rapidly alternating images on the screen with lenses that alternate which one blocks or transmits.
When you look at something in real life, because there is a distance between your eyes they recieve slightly different images. Your brain patches them together in a way which allows you to “see depth”.
If you want to see something in 3d being projected from a 2d screen, you need to make your eyes recieve distinct images that “capture” the depth, albeit in an artificial way.
Coloured glasses did this by basically showing a blue and a red image on top of each other, each corresponding to what each eye would “see”. The coloured glasses just filter one image each, so you get distinct images in each eye.
More modern 3d movies use polarisation instead of colour. Basically (and this is not exact, rather ELI5) the image that they want your right eye to see vibrates up and down, the image for your left eye vibrates left and right. The right lens has a grating that vertically, so the left-right vibrating image gets blocked but the up-down image passes through, and vice versa in the other eye.
I’m not sure how glassesless 3d works, I know of some prototypes that used gratings slightly offset from the original image, so the light that passes through is different depending on where you view it from, I think the Nintendo 3ds used this. The big problem is you have little flexibility in viewing angle.
Stereoscopic vision works because your right eye sees slightly to the right of things and left slightly left.
To produce a stereoscopic image, a projector projects one image recorded to the left and one to the right slightly.
These are then projected at a slight offset from each other, but we have to find a way to make it so only one eye sees one image.
We used to do this by displaying two different color-altered images and wearing colored lenses. A red lens won’t let blue light through and a red lens won’t let blue light in. This allowed the right eye to see the left image and the reverse for the other eye.
Now, we can use polarization to do this.
Think of polarization as “lining up” waves of light. Instead of absorbing, reflecting, and passing based on color, it does do based on alignment.
One image for one eye is polarized in one way and the other eye the other. We’ll simplify by calling the left lens vertical and right horizontal, though they’re usually polarized a little more complexly than that.
Now, they project one image using vertically aligned light and the other with horizontally aligned light and they’ll inky make it through the respective lenses!
Of course, there’s a bit more complexity to it, but that’s the gist!
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