Staff at two Oxford companies helped to create the stunning special effects for the Christmas blockbuster The Golden Compass.

As well as being filmed in Oxford, the movie used pioneering camera systems made by OMG (Oxford Metrics Group), based in Botley, and digital crowds created by Audiomotion, of Osney Mead.

One of the biggest challenges for the filmmakers was creating hundreds of characters - including polar bears, witches and other imaginary creatures - for the giant battle scenes.

New Line Cinema, the studio behind The Lord of the Rings trilogy, used a technology called motion capture to create a 'gyptian' crew for the film's Noorderlicht ship and to create 'digital extras' for a huge battle that pitches Golden Compass heroine Lyra, played by Dakota Blue Richards, against Tartar guards.

In the story by Oxford writer Philip Pullman, the gyptians are boat people, similar to gipsies.

Audiomotion, now Europe's biggest motion-capture studio, created a replica of the gyptian ship, using rigging from the Cutty Sark restoration company.

Cameras were used to film a group of stuntmen fighting on the rigging in the Osney Mead studio, and the images were replicated hundreds of times.

Managing director Mick Morris said: "You can get the stunt guys to do things which would be too dangerous in practice.

"When movie people shoot the live action, they will populate just the front two rows of an army with extras, where there should be thousands of soldiers behind them.

"If you can see it when the film is released, someone hasn't done their job."

More than half the motion-capture cameras used by big movie studios are made by Vicon, part of OMG.

The technology was developed by Oxford engineering don Julian Morris, for surgeons to measure the movement of children with cerebral palsy.

The actor or stuntman (or animal - dogs and cats are also used) wears a close-fitting black lycra body suit covered in small glass reflective spheres.

As the actor moves, special cameras, which can see only the markers, take hundreds of photos very quickly.

The software converts these images into three-dimensional film. Robbie Williams and Wayne Rooney are among stars who have been converted into computerised 'skeletons' by Audiomotion - for a pop video and a computer game, respectively.

It is now used by coaches analysing the bowling techniques of cricketers, road engineers and satellite navigation systems as well as movie directors creating fantastical characters and computer game makers.

Nick Bolton, who runs Vicon's parent company OMG, said: "Any time that you want to understand human movement in three dimensions, our technology is there.

"We are now building a business using the technology in other areas such as unmanned aerial vehicles for surveillance."