Digital film projectors

March 27, 1999

Cinema owners would love to do without projectors and heavy reels of film. At last, digital technology has provided a feasible alternative

THE movie industry has changed quite a lot since the first motion-picture projectors sputtered into life in 1895. The business of capturing moving images and then projecting them on to screens in front of paying customers has steadily improved, with talking pictures, colour, widescreen formats, digital special effects and fancy sound systems. But one aspect of the technology has remained stubbornly unaltered: its dependence on mechanical projectors and reels of film. Only now, over a century later, has a good alternative been devised.

It is not hard to see why distributors and cinemas would like to do away with celluloid. The reels are a metre-and-a-half (five feet) in diameter, and can weigh as much as 30kg (around 60lbs). Each print of a film costs some $2,000 to make, and since a major movie requires as many as 5,000 prints in America alone, duplication and distribution are a huge exercise, with fleets of lorries delivering prints to cinemas in the middle of the night. And, worse than that, prints start to deteriorate after as few as 30 showings, with scratches, dust-marks and popping sounds diminishing the quality.

How much easier it would be if movies could be distributed by satellite or high-speed networks, stored on hard disks, and played at the press of a button. Duplication and distribution costs would vanish; rural areas would not have to wait for many days after a release for their print to be delivered; cinema owners could juggle schedules more easily; and sound and picture quality would no longer deteriorate, no matter how many times a movie were run. It would even be possible to show live events, such as boxing matches or baseball games, in cinemas.

There is just one obstacle to the arrival of this cinematic paradise. The technology exists to encode and transmit movies in digital form, to compress them for storage, and to encrypt them to stop illegal copying. But there has, until recently, been no way to project the result on to a screen. Digital projectors have been unable to deliver the bright, sharp, colourful images that are possible with old-fashioned celluloid and mechanical projectors. Instead, they produce faint, washed-out colours—as anyone who has ever watched a large screen at a conference or a rock concert knows.

In the past few months, however, two new kinds of digital projector have been making waves in the movie industry. At last, digital projectors may be able to compete with film. As a result, a consensus has emerged that it is now a matter of when, rather than if, the industry will go digital.

Lights! Mirrors! Action!

How seriously the new technology is being taken was demonstrated earlier this month when George Lucas announced that his company, Lucasfilm, will stage a test of the two rival versions in June, during special screenings of “Star Wars: Episode I”. Four cinemas (in two as-yet unnamed American cities) will take part. Two will use projectors from Texas Instruments, and two will be equipped with hardware made by Hughes-JVC. This will be the first time that paying customers have seen full-length motion pictures projected digitally, rather than from celluloid.

Both kinds of projector rely on technology borrowed from smaller projectors that are commonly used in, for instance, corporate presentations. At the heart of the Texas Instruments “digital light processing” (DLP) projector is a rectangular array of 1.3m tiny aluminium mirrors, each of them 16 millionths of a metre wide. Behind the mirrors is a memory chip, each cell of which corresponds to one mirror. The operation of electrostatic forces between a mirror and its cell means that loading the electrical equivalent of a “1” into the cell causes the mirror to tilt 10° in one direction; a “0” causes it to tilt 10° in the other.

When combined with a suitable light source and projection optics, the array of mirrors can project an image. Each mirror acts as a beam-steering device, controlling whether a single picture element (pixel) in the image is light or dark. Shades of grey are created by tilting the mirror backwards and forwards thousands of times a second to vary the brightness of the pixel it is projecting. Colour is added by using three separate arrays, each fitted with a filter for one of the primaries—red, green and blue—that, in combination, produce a full-colour image.

The Hughes-JVC projector uses “image-light amplification” (ILA), which also relies on reflection, but otherwise employs a completely different approach from the Texas instrument. The red, green and blue components of the signal are fed into three separate high-definition cathode-ray tubes (in effect, fancy black-and-white televisions).

In each case, the resulting image is focused by a clever arrangement of lenses on to a three-layer sandwich made of special materials. The first layer of the sandwich is photoelectric. Light falling on to this layer creates an electric charge. That charge, in turn, affects the third layer, which is made of liquid crystals. Applying an electric charge to the liquid crystals causes the molecules they are made up of to realign themselves, altering the transparency of that layer. (The screens of portable computers work in a similar way.) The result is that a high-resolution negative copy of the moving image is formed in the liquid-crystal layer. This negative is illuminated from the front by an arc lamp, and the light from this lamp passes through the transparent regions of the liquid-crystal layer to the middle layer. This is a so-called dielectric mirror, which reflects almost 100% of the light that falls on it. Add appropriate filters, and the whole thing produces a full-colour moving image.

Both technologies have advantages and disadvantages. Texas Instruments claims that its DLP system is superior because it is entirely digital. The movie streams straight off the hard disk into the mirror arrays, and thence on to the screen. Hughes-JVC, on the other hand, says that ILA, in which the signal is converted to analogue form, is smoother and better because it makes no assumptions about the number of pixels in the original digital signal. At any rate, both systems are said to be at least as good as, and probably better than, film, which looks jittery and flickery in comparison.

The biggest hurdle facing digital cinema is financial not technological. At around $100,000 each, the new projectors cost two or three times as much as conventional ones. The switch to digital may thus produce savings for studios and distributors, but it will cost cinema chains money.

Cinecomm Digital Cinema, a Los Angeles-based company that is promoting the Hughes-JVC system, thinks it has an answer to this. It plans to buy the new projectors and lease them to cinemas on a per-showing basis, while handling the distribution by satellite. Cinecomm (and similar, rival companies) would then extract distribution fees from the studios.

Not everyone likes the sound of this, because it would put intermediaries such as Cinecomm in an extremely powerful position. But if history is any guide, the switch to digital projection may be inevitable. Mr Lucas, who pioneered computerised special effects in the 1970s, plans to shoot his next two “Star Wars” films with digital cameras—eliminating film altogether. He hopes that digital projectors will be commonplace by the time the last of the trilogy is ready. If he is right, digital technology may herald the death of film, but another rebirth of movies.