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How is 3D created?
The world which we see has three dimensions – height, width and depth. Our eyes however can only see two of these dimensions. The act of seeing anything starts when the eye lens focuses an image on a membrane called the retina. This image is two-dimensional. But, evolution has put our eyes in the front of our face. This enables our eye lenses to produce a slightly different image in each of the two retinas. The retinas transmit the image to the brain, which uses the parallax or the slight difference between the angles of the two 2D images to extrapolate the depth. This type of vision is called stereoscopic.
How is a 3D film made?
While making a 3D film, filmmakers project two similar images shot from different angles simultaneously on the screen. In the older days a 3D illusion was created by using anaglyph images. The films had two different layers. These layers with two different colours, typically red and green/blue, were superimposed in a way to counterbalance each other. On screen, the two predominantly red and green/blue images were projected by using a single projector. The audience were given 3D glasses with one red lens and the other blue or green depending upon the colour of the film. The red part of the image was obstructed by the green lens and vice versa. This enabled the two retinas to form two different images and hence the optical illusion of depth was created. However, the colour filtering by the lenses distorted the final colour and many in the audience watching a 3-D film complained of headaches and nausea. The picture quality was also low and hence 3D did not take off even though the first such film was screened as early as the 1920s.
What is polarization of light?
Like the expanding ripples created by a stone dropped in water, light is also a disturbance or a wave that travels in space and time. But unlike the simple ripple in water, light is a rather complex wave. In the case of light, the angles of vibration can vary through 360 degrees. Ordinary light from the sun or a light bulb is made up of many waves with different wavelengths and different angles of oscillation. Now imagine what would happen if a filter was devised so that these waves vibrating in different angles were made to vibrate in a single plane or the pre-adjusted angle of the filter. The light would now vibrate in a particular angle and to view this light one would have to wear glasses which have filters similar to these angles. A projector or two projectors can project light on the screen which is differently polarised; say 45 degrees and 135 degrees. The light waves whose plane is polarised by 45 degrees can only be viewed by glasses which have the same angle of polarization. Now, if 3D glasses have differently polarized lenses, both can receive different images and hence the optical illusion of depth could be created.
What are the different types of 3D glasses?
All types of 3D glasses can be divided into two categories: passive and active. Active 3Dglasses interact wirelessly with images on a screen to enhance 3D viewing, whereas passive glasses do not. Passive 3D glasses are divided into two major subcategories: anaglyphic and polarized glasses.
Practically anyone who has ever seen a 3D movie is familiar with anaglyph glasses, which feature a combination of red and blue lenses. Anaglyphic 3D works by projecting two identical but slightly offset images on a screen, each image tinted with a different color. To the naked eye, an anaglyphic image appears blurry, with reddish and bluish hues. The glasses use color-filtering lenses to target one image to the right eye, and another to the left; the result is that each eye sees a different image, but the mind is tricked into believing it sees only one. The mind compensates for this by focusing in between the two offset images and blending them into one, which creates an illusion of depth.
Passive polarized glasses operate on the same basis as anaglyph glasses, only they filter light waves rather than color. Again, two identical and slightly offset images are superimposed, except in this case each image is polarized to project light differently than the other. With polarized 3D glasses, each eye only processes one image. Again, however, the mind is tricked into blending the two images into one, creating a 3D experience. Unlike anaglyphic 3D, which can be projected from any screen, polarization 3D works best with screens able to relay different light frequencies without sacrificing picture quality.
Which 3D technology is more preferred in 4D 5D theaters?
With the advent of 3D technology, especially passive, 3D viewing has been able to reach exceptional heights with the help of purposely made animation movies for 4D 5D theaters. The passive polarized glasses are of two types as mentioned above – anaglyphic and polarised. With passive polarized glasses 3D viewing has become more articulate.
Anaglyph glasses use two different color lenses to filter the images. The two most common colors used are red and blue. If you were to look at the screen without your glasses, you would see that there are two sets of images slightly offset from one another. One will have a blue tint to it and the other will have a reddish hue. If you put on your glasses, you should see a single image that appears to have depth to it. The red lens absorbs all the red light, cancelling out the red-hued images. The blue lens does the same for the blue images. The eye behind the red lens will only see the blue images while the eye behind the blue lens sees the red ones. Because each eye can only see one set of images, your brain interprets this to mean that both eyes are looking at the same object. But your eyes are converging on a point that’s different from the focal point — the focus will always be your television screen. That’s what creates the illusion of depth.
Today, a more popular type of passive lenses in movie theaters can be found in the polarized glasses. Again, if you look at a screen that uses this technology you’ll see more than one set of images. The glasses use lenses that filter out light waves projected at certain angles. Each lens only allows light through that is polarized in a compatible way. Because of this, each eye will see only one set of images on the screen.
Polarized lenses are becoming more popular than anaglyph glasses because the glasses don’t distort the color of the image as much and provide a better audience experience. With dual projectors on a silver screen it is easy to project such images.
