The magic behind the making of Brave

That's in addition to all the people who worked in the music, animation, sound and animation departments. The entire crew list isn't quite as long as the actual film but it's a close thing. At the height of the prolonged exercise, Pixar had a few hundred employees beavering away. The production budget is said to have come in at $185 million.

Thus the responsibilities of the director (or directors, in the case of Brave) are onerous. Brad Bird, who directed The Incredibles and Ratatouille, has likened the process to "getting hit from a million different angles, having a barrage of questions - Everyone just wants the answer but from your perspective it's like you're being hit left and right and sometimes you don't even know after a while what anybody's talking about."

A new book, The Art Of Brave, tells the story behind the movie, from original director Brenda Chapman's concept to the hiring of senior crew (head of story Steve Purcell, production designer Steve Pilcher, producer Katherine Sarafian) and a couple of field research trips to Scotland, the first of which took place in 2006. The visits saw the director and the story and art directors filling notebooks with drawings, colloquialisms, song lyrics, snippets of conversations – anything that could help Pixar get further into the essential Scottish element of the story.

Scots-born Gordon Cameron, who was global technology supervisor on Brave, explains: "At this time the crew was very small. They wanted to establish a look and a colour palette for the film so that by the time the technical crew came on board they had a fairly solid idea how the film would look: what the various seasons would look like, how realistic you want the characters to be, and how important all the other elements are."

Back at Pixar's base in Emeryville, northern California, the characters and various scenes began to take shape in pencil or acrylic sketches before being rendered digitally, the plot was painstakingly storyboarded and the look was designed and tweaked. The list of crew members grew and grew. Eventually, the stage was set for the actual animation, the crown jewel of the process, the place where the performance actually happens.

This is where the simulation department came into play. One sub-department focused on the character's hair or fur, a second on cloth, tapestries and costumes, and a third – the shot technical directors – ensured that hair and clothing moved with the characters and in the wind. Just look at Merida's red hair bouncing as she races through the forest on her Clydesdale horse, Angus, and you will realise this was no easy task.

A key role in the animation is played by the colour scripts, which visually orchestrate the overall lighting, colour, weather and time of day. However, some 90% of the work on the colour script had to be jettisoned when it was decided that there would be no snow in the film.

The book also quotes Danielle Feinberg, director of photography for lighting, as saying that Brave's forest "is one of the most complex things we've ever done", with extremely complex characters riding through the forest. "The complexity, when you're trying to bring those shots to the big screen, is mind-boggling."

And, all the time, the directors have to ensure that everything that is done is absolutely in keeping with their vision of the finished film. You begin to understand what Brad Bird means when he says it's like getting hit from a million different angles.

Cameron, 44, who is from Banff, Aberdeenshire, has worked on the animation side of Pixar's business for several years, starting with Finding Nemo and going on to The Incredibles, Cars, Ratatouille, Wall-E, Up and Toy Story 3. He flew home to attend the premiere of Brave in Edinburgh. The day after we spoke, he faced a 20-hour trip back to California.

He said: "From the start, Brenda, the director, had a very particular idea about how she wanted the film to look. Merida's hair was important and we knew it was a challenge, because curly hair has never been done particularly well in the past in computer graphics. We've done bob haircuts or ponytails in previous films but it was super-important that Merida had this particular personality. From the very first sketches it was all about her hair.

"What tends to happen is that we try to reuse as many of the [software] tools that we used in previous films when we can, but for Brave we knew we had the curly-hair challenge and also that we wanted a much more realistic, if stylised, look than our previous films.

"Lighting was important, the vegetation and scenery were much more important, the water was even more important, and there were also the crowds.

"The goal is to try to nail down the story as much as possible early on, partly because we don't have infinite budgets.

"We need to know what the technical challenges are early on so that we can throw people at it."

He said he was "particularly proud of the way it all holds together, with the hair simulation, the animation, interaction with fluid and skin/flesh and muscles all playing together, so you hopefully don't notice the individual elements but, seen together, they feel right."

A pivotal scene in Brave sees Merida (voiced by Kelly Macdonald) having a furious argument with her mother, Queen Elinor (Emma Thompson), then slashing at a wall-hung tapestry. Like other scenes, this was storyboarded carefully so that any problems could be anticipated in advance of any digital content.

"You work out what elements are going to be in the scene, you try to call out any elements that will be problematic, like the slashing of the tapestry," says Cameron. "By that stage you know the tapestry is an important story element, and it has to survive cutting

"So you spend money developing a 'weaving' technology – all the garments in the film, and that tapestry in particular, are all digitally woven rather than just being textures. There's a procedural geometry involved so that you can see the actual stitches, and you can see the weave, so that when the tapestry is cut, you can see the exposed threads.

"Then you will come up with some technology to be able to do the slashing motion, and have it work when you simulate it properly."

That scene, Cameron acknowledges, is one of his favourites in the film: "There is so much emotional stuff going on, and so much acting. It's pretty dramatic, so it's important that the scene doesn't contain anything that doesn't feel just right.

"What makes it interesting for me to be there – and I know a lot of people at Pixar often say this – is that you want to know technically how to model reality. We're not interested so much in depicting reality as using reality and then bending it to give you something that is believable, so that the world feels consistent. People will say Brave looks very realistic, and I'm hoping that because it's reminiscent of something that they know, the pieces fit together and give them a particular feeling."

Like other Pixar features, Brave was first screened at a wrap party for its employees and their friends. "Someone has built an Italian castle in the Napa Valley – it's the craziest place you've ever seen – so we rented it and had a party," Cameron says. "Everyone really enjoyed the film. It's amazing to see it actually done, especially when you work on it for so long.

"You see the individual pieces over and over again but very few people will see the whole film while it's being put together. For me, it's amazing to see the whole thing. Seeing all the disparate pieces come together is pretty spectacular.

"But what's weird is that you finish the film and have the wrap party, then the film usually isn't released for a few weeks, so you have this sort of dead zone. You have no clue as to what people are going to make of it at all. It's exciting when it starts to show in theatres. I like to see it in a cinema without anybody from Pixar ..."

He sums up Pixar's philosophy thus: "All we want to do is to make movies that people will want to see and that we enjoy making. It's really nice that we've been successful, crazy that we've been so lucky, but we don't take it for granted. Back when we were about to release Finding Nemo, we were thinking, 'Oh man, are people going to like this?'. We really had no clue."

Early box-office returns for Brave indicate that there need be no cause for concern. As of last Monday, it had grossed an estimated $197m in the US and $47m overseas. Expect these figures to grow substantially in the weeks ahead, not least when Merida finally comes home to Scotland. Brave – and its feisty, red-headed heroine – are shaping up to be Pixar's lucky 13th. n

The Art Of Brave by Jenny Lerew is published by Chronicle Books, priced £25.