Creating galaxy-wide space battles? No problem. Showing prehistoric dinosaurs rampaging through New York? Easy peasy. Simulating a Hoxton Fin? Impossible. For years, the one challenge that has had computer animators scratching their heads is creating a realistic head of digital hair.

‘ Simulating a mass of curls is one of the most complex problems out there,’ says Frédéric Leroy, Director of the Physics Department at L’Oréal’s Advanced Research Laboratory. A typical head (Matt Lucas and Patrick Stewart aside) will contain between 120,000 and 150,000 individual strands of fuzzy, wispy, straight or permed hair, each of which moves independently when you move your head, talk or simply stand in the wind. ‘Motion is the hardest part to simulate,’ says Leroy, ‘Up until now, computer models just haven’t been able to render moving hair in a realistic, physical way.’

The problem is that if you try to copy hair and get it wrong, the results look terrible. The film Final Fantasy: The Spirits Within was the first computer generated imagery (CGI) movie that attempted to show realistic people. Unfortunately, despite accurate skin colouring and smooth movements, its digital characters made many people feel uncomfortable and the movie flopped at the box office. Its seems that while we like animated toys, robots and animals, digital people often just look weird – and much of that distaste is due to stiff, unnatural virtual haircuts.

Leroy notes that, ‘Even if you look at the latest animation titles like the Incredibles, moving hair isn’t computer generated – it’s still drawn by hand.’ Ken Bielenberg, Visual Effects Supervisor on Shrek 2 developed what he calls ‘the wig system’, a process of animating hair that combines computer-generated motion and manual movement, controlled by the human animators. An actual wigmaker was employed to help animators understand how wigs are made and the colour and shape patterns that go into creating various hairstyles.

This is the problem that researchers at L’Oreal’s Advanced Research Laboratory set out to tackle and, after five years of pulling their hair out, they finally think they’ve finally cracked it. ‘We started by modelling the physical characteristics of one single strand of hair. Even with powerful computers and the latest algorithms, that took two years,’ admits Frédéric Leroy. ‘Then it took three years to integrate that single fibre into a model of a head of hair. But we’ve now got a well rendered and physically realistic description of hair. That’s not just its look, but also the physical constants that let us predict changes to its shape, colour and movement when treatments are applied.’

L’Oréal is already using its digital model to develop new hair care products faster and with less reliance on costly real-world experiments. It expects the first digitally-developed products to be available shortly. But the possibilities of making the model widely available are endless, says Leroy: ‘It could help hairdressers design new haircuts. Soon, salons will be able to show customers in advance exactly what their hair will look like after cutting, brushing, perming or colouring treatments.’

‘ We’re also confident that the film and games industries will be very interested in our model,’ says Leroy. He’s not wrong. The success of characters like Lara Croft, currently debuting on mobile phones in Tomb Raider: Legend, depends on how natural they look. Simon Protheroe, New Media Director at Eidos says, ‘The current generation of handsets enables us to get Lara’s trademark ponytail, which has always been a key feature of the character, looking right in the 3D mobile environment for the first time.’

That’s all very well on small phone screens but the arrival of High Definition movies and gaming into our living rooms demands a whole new level of detail and realism. Frédéric Leroy from L’Oréal says, ‘The simulation process is constantly running, and always improving. The next step is to move on to skin, although we then have to consider a very complex mixture of mechanics, physiology and optics.’ It seems that while digital shampoo is just around the corner, virtual make-up might take a little longer…

Right hair, right now
If 150,000 hairs on a human head sounds like a lot, spare a thought for the animators of Mumble the penguin in Warner Brothers’ holiday movie Happy Feet. His fuzzy body contains over six million individual feathers, each of which reacts to water, ice and light in its own way. Happy Feet took almost four years to make and, according to director George Miller, ‘Over half that time was spent in creating the digital pipeline. Hundreds of people came from all over the planet to work on the film – and a large proportion of them were maths wizards as well as artists.’ Producer Doug Mitchell says, ‘The amount of processing dedicated to this project would have been impossible to achieve only a few years ago. We pushed the computers to breaking point.