3D Cinema - How it works

Jake Carroll finds the depth behind the 3D screen, and explains how it all works.

Movies have a pretty powerful effect on popular culture. It's no surprise that the movie industry also has a tendency to drive technological innovation and create consumer demand. What we see in today's movies ends up feeding into the technology that we have sitting in our GPUs at Christmas time the next year. It probably isn't a coincidence that this year, the movie industry pushed 3D cinema back into our line of sight, and as a result, a torrent of 3D display panel technology, consumer video card driver enhancements and strange looking eyewear has popped up. This month, we're all about the third dimension. Hopefully it'll jump off the page at you.

3D Cinema was not the first instance of 3D entertainment, let alone technology in visualisation. The first such device was known as the Stereoscope and was invented by Sir Charles Wheatstone in 1840. The illusion of depth in a viewfinder was mainly used for entertainment purposes, but also for photogrammetry, a technique for measuring and determining the geometric properties of objects through photography.

3D viewing, and the perception of depth in real life, let alone a movie or image is a function of a wonderful ability that humans have known as binocular vision. Binocular vision does a few things for us.

1. If we somehow end up in a situation where we lose an eye - we've still got a spare to fall back on. Call it RAID1 for eyes.

2. Because we have two eyes independent of each other, with an ability to be controlled independently (although for the most part, this is subconscious), the light that bounces through to the back of our eye, and ends up as images to our brain, come at slightly different angles. This has purpose in depth of field (DOF) perception. Because of this built in ability, we can judge distances of objects in front of us, or estimate lengths of objects.

3. We're able to apply a technique to our vision known as binocular summation, meaning we can make out or determine faint objects at distance through physics internal to the eye, and inference about what we can see.

We've got a good thing going for us as animals that evolved with more than one eye, Futurama aside.

The concept of stereo DOF or the illusion of a flat image being given depth is a result of binocular vision. When a user sees two images, each ever so slightly differing in angle or tilt, representing two different perspectives, with a slight deviation exactly equal to what the eyes naturally perceive in binocular vision, the impression of depth is given.

The images used are offset slightly in angle, colour, hue and contrast, so that there is an obviated differentiator between each eye. Without this differentiation, the 3D effect is not as obvious or strong. Additionally, the ability to perceive depth differs between every individual.

There are yet other methods of 3D viewing without the aid of external apparatus. One such method is known as a random dot auto stereogram, which allows a viewer to perceive a 3D image by diverging their eyes whilst looking at a 2D image. Software can be used to achieve this, with a dithering and image dispersion algorithm being used to inference a shape or cross sectional image into a seemingly random reoccurring pattern, which, when viewed with diverged eyes meshes together to form a 3D relief. 

Things get wearable from here on in. In the 1940s a film recorder known as the 'Stereo-Realist' system was created to put this stereoscopic effect into motion video. The idea was that the user would wear a stereoscopic set of lenses that showed an image through each piece of glass slightly offset. The technology didn't really work very well. People got motion sickness, headaches and generally, puke buckets were a standard issue in the few viewing locations that existed. Epic fail.