Tuesday, November 13, 2007

Physics-based cartoons

Remember when our family went to see Ratatouille? Mark posted about it and I commented that the fur and water motion was soooo realistic.

One of my coworkers gave a talk about his PhD work simulating water flow and rendering it in 3D. It took a long time on a supercomputer to make the movie he showed of water being poured into a glass. The sewer scene in Ratatouille reminded me of my coworker's PhD work.

Sure enough, this month's Physics Today has an article called Animation uses old physics to new effect which discusses recent technical breakthroughs in animation. The article cited the scenes that most (technically) impressed me in Ratatouille.
Achieving visual realism with physically based simulations while taming the result to fit artists' imaginations is the goal in animated filmmaking and gaming.

Ever wonder how animated films such as The Incredibles get hair, clothing, water, plants, and other details to look so realistic? Or how, like the lion in The Chronicles of Narnia, animated characters are worked into live-action films? If not, the animators would most likely be pleased, since they don't want special effects to distract from the story. Behind the scenes, though, is a lot of artistry, computation, and physics.
My coworker told me the real reason that the Incredibles do not wear capes. It is not because they are so dangerous to the superheroes. They just put that in the storyline to help justify the lack of capes in the movie. Apparently, it is very difficult to make physics-based animated capes show up only behind the superheroes. Sometimes, the capes pop up through the figures and show up where they shouldn't.


  1. Hmmm, that's really interesting. I guess I never stopped to think about how much work must go into making animation feel "real". A friend of mine who started a ph.D. in physics at Berkeley, but left midway through to go to design school is now working for Peter Jackson's special effects company in New Zealand and told me that Ratatouille is one of his favorite films. Now I know a little more why!

  2. During grad school, I used to make animations of molecular dynamics simulations. It was so cool to make molecules 'dance'. It was quite crude by Ratatouille standards, but it made me happy.

  3. I liked The Incredibles, but I thought it borrowed heavily in places from the graphic novel Watchmen (which itself borrows-freely-bordering-on-plagiarism in certain places).

    The "capes are impractical" idea was in Watchmen too.

  4. Not only do they model the physical reality of the depicted phenomena, but computer animators also model reality as it winds up on film. This includes phenomena such as lens flare (which shows up in every Pixar film) and different types of focus. Strangely enough, things seem more real when the artifacts of photography are replicated. Recall that black and white was used throughout the 50s and 60s for movies that wanted to appear "realistic", whereas color provided a hyper-reality.