The makers of the latest Disney animated blockbuster "Tangled" say one of the biggest challenges was making Princess Rapunzel's long flowing hair seem realistic, including in 3D.
Disney's 50th animated feature is based on the Brothers Grimm fairytale and fits into the long tradition of a studio that brought children's classics "Dumbo" and "Cinderella" to the world decades ago.
But moviegoers can be forgiven for being reminded of films by younger animated movie rivals Dreamworks (with "Shrek" for example) and Pixar, of "Finding Nemo" and "Toy Story" fame.
"There's a look in the film that kind of relates back to the Disney animated from the 40s and the 50s," said Nathan Greno, co-director of the movie, which opened Wednesday on the eve of the Thanksgiving holiday in the United States.
"But because it's been made by computer, it's so fresh it's so new, it's unlike anything audience have seen. We really tried to have one foot in the past and one foot firmly planted in the present," he told AFP.
The film - initially called "Rapunzel" but changed to reflect the boosted role given to her charming rescuer - tells the story of the princess born with magic hair but trapped in a tower.
She is saved by bandit Flynn Ryder - voiced by Zachary Levi - but that only marks the start of her real journey.
"The core of the script is this coming-of-age story with this girl trying to find herself," said Greno's co-director Byron Howard.
"We did look at the original Grimm's fairytale, which is very dark and kind of confusing in a lot of ways. And we tried to take the best part of that and expand it to something epic and huge."
In addition to its narrative drive, the film used the very latest hi-tech advances in computer-generated graphics - in particular for the princess's river-like hair, splashed across giant publicity posters for the movie.
"The biggest challenge has been to raise the bar, the artistic bar, the animation bar for the human characters," said animator Carlos Cabral.
"The hair was a huge technical bar that we had to achieve. The interaction of the hair with the clothes and multiples layers of clothes really kind of raised the bar on CG character animation."
Cabral said it was particularly difficult to simulate hair because every strand of the princess's locks had to be reproduced.
"And every hair has to collide with everything. This is a huge calculation. Literally up until recently, we haven't had the computing power to be able to get even close to that," he added.
The latest technology also helped the animators give the characters expressions reflecting the actual faces and movements of the actors who lend their voices.
"I saw Flint's face when I first auditioned for the role, they had pretty much already conceived it. And I thought, 'Well it's a good looking guy!,'" said Levi.
"There's a camera in the voice-over booth, kind of picking up your movements and facial expression. There's a little bit of you in the character."
Voicing characters - a growing source of income for actors amid the explosion of animated movies in recent years - presents unique challenges.
"It was very strange not being able to have like a give-and-take with another actor," said Levi.
"You always have to use you imagination to picture the world. At least in a live-action show you have all this things that help you to picture this fictitious world.
"In voice-over, it's all about imagination."Reuse content