A Beginner’s Guide to … 3D entertainment
Don't know your passive display from your active glasses, then read on for everything you need to know about 3D.
A TV, PC, projector or cinema screen is essentially flat, but even when we’re watching normal 2D footage we choose to ignore its flatness when viewing a picture that simulates a 3D world, such as a film. It’s not hard, because the image is packed with clues to help us understand the 3D space it attempts to simulate: perspective, familiar sizes and so on.
We can get caught up in the excitement of a horror film, but we don’t really believe that the on-screen monster is about to burst through the screen and terrorise the audience. It was different for the first people ever to attend the cinema in 1895, though. They famously fled the building for fear of being run over by the train that loomed before them on the screen.
Today, 3D cinema sounds echoes of this historic event. Dennis Laws, Technical & General Manager at the BFI Imax in London, describes the reaction to the animated short film Paint Misbehavin’, where “the entire audience is trying to catch these globules of paint which appear right in front of their noses.” The 3D effect is not only so convincing but also so unexpected that viewers struggle to believe that’s just an illusion.
That illusion works when a screen is able to transmit different images to the left and right eyes. With control over what each eye sees, it’s possible to simulate the stereoscopic effects – stereopsis and convergence – by offsetting the viewpoint of one eye compared to the other.
CINEMATIC DEPTH
The theory behind 3D visuals is fairly simple but it’s not so easy in practice. First, you need two discrete images that interact in a meaningful way to create a 3D effect. Then you need a system that sends each image to the correct eye and that eye only.
Classic anaglyph glasses, great if you don’t mind watching in blue and red
Cinemas have experimented with various techniques over the years. The most memorable one for most people will be the anaglyph approach with its distinctive red and green glasses. This works because a red line will look red through the red filter, but black through the green filter. A green line has the opposite effect. This makes it easy to separate the left-eye and right-eye images, simply by converting them to monochrome green and red images. No special projector is required and the glasses are cheap.