Computing: Could computers kill the soap opera star?: Actors, watch out: technology may eventually enable us to simulate images of real people. Steve Homer reports on a digital revolution in broadcasting

THE WORLD of television is changing - the computers are taking over. This doesn't just mean that automated systems play pre- recorded tapes in the middle of the night without the intervention of human hand, it means everything from computer-based editing in the studio to the transformation of the TV set in your living room into a computer. It could even mean a computer-generated actor appearing in your favourite soap.

The big change lies in the digital representation of TV images. In the 'good old days', TV pictures were stored and manipulated as squiggly waves representing the colour and brightness of each line on the TV screen. These analogue systems are dying. The world is turning digital.

In a digital TV image, pictures are represented by little blocks of discrete colour, each with a code for its precise shade and brightness. With enough of these elements, you can make up a beautiful picture.

TV stations all over the world are moving to digital for production and in- house working and, over the next few years, they will start digital transmissions to the home. Channel 4's new headquarters, for example, is all digital and the signals stay digital all the way to the transmitter, where they are then converted to the analogue PAL TV system that domestic TV sets use today.

But what is so good about this technology? The answer is flexibility and robustness. 'Digital pictures stay clean pretty much whatever you do to them,' says Chris Daubney, chief engineer at Channel 4. 'You can store them in lots of different ways and they are much easier to manipulate without introducing undesirable effects. Once you have made the investment in digital systems, life becomes much simpler.'

Digital is more robust because the data contains additional information to correct any mistakes. If there were a minor scratch on a digital video tape, for example, a new, perfect copy could be made, even though the original was damaged.

But it is the flexibility of digital information that is really intriguing. For a start, you can suck the information into a standard computer and manipulate it in many ways. At its most basic, you can put the data on to a computer hard disk, which can then be used for many different broadcasting tasks. Instant access to any part of the disk means that controlling the insertion of advertisements into programmes is simple, and editing a doddle.

The big problem for disk-based systems is that a video takes up a huge amount of storage. For broadcast-quality images, you need up to 4,050 Mbyte per minute of output. But for critical tasks, although disks work out about 1,000 times as expensive as tape, this can be worthwhile.

Editing on a hard disk, for example, is much simpler than on tape-based systems. An editor can jump to different parts of the disk surface in milliseconds, and re-order scenes in a matter of seconds.

Computerised digital video images are also being used to create special effects in films and advertisements. These same techniques are coming into ordinary programmes. A camera crew reflected in the wing of a car during shooting, for example, can be digitally removed. You can also add detail and alter reality - the leaves on the trees could be turned from summer greens to autumn russets.

Ultimately, computers could simulate live actors. Hollywood agents are already putting clauses into contracts to control the electronic image rights of the star. The reason is simple: computer simulation and graphics technology are becoming so clever that, conceivably, a star could be fired from a movie and scenes shot using a simulated actor. The technology isn't there yet - but it will be.

Digital TV is coming right into the home. In fact, in a way, it has already arrived. Interactive products such as CD-i and games machines from Sega and Nintendo store their images and storylines in computer form either in cartridges or on CDs. Next year BSkyB is expected to start test transmissions of digital pictures by satellite. You will need a new box to receive them but, if the system is implemented properly, you should get crystal-clear pictures.

Cable companies are also likely to start digital TV within one or two years and the BBC hopes to start digital transmissions in 1997. Again, the pictures should be crystal clear. Many new services should be possible, particularly on cable TV, using what are essentially computer networking techniques.

In many offices around the country people use local area networks to link up their computers. A message for a computer goes around the network with a certain address on it. This is only read by the specific computer and all the others ignore it.

Cable TV will use the same type of technology. So you will be able to send a message back to the central computer of the cable TV system saying you want to watch a specific movie or play a game and it will be able to send messages to you. These (digital) messages will in fact be the movie that you requested, delivered to the screen as you watch.

Within 10 years, every aspect of TV will be digital and broadcasting will have become a computing enterprise. There will still be a role for the creative spirit, but if you want to get ahead in broadcasting perhaps you should start with a computer science degree.