Archive notice: This article was originally published on February 1, 2010. Links and embedded videos are preserved as part of the historical record.
A new approach promises naturally animated trees for games and films instead of static background graphics. Computer scientists Peter Hall and Chuan Li at the University of Bath have developed software that learns to create realistic animations using video recordings of real plants. The computer then creates natural-looking forests whose trees also move in the wind. The simple method is suitable not only for big-budget Hollywood blockbusters.
At first, the approach sounds similar to the motion-capture process used to animate humanoid beings, as in the 3D film Avatar. “Trees present a more complex problem. Branches look very similar and obscure one another when they move,” Hall emphasises in response to a question from the pressetext.de news service. Reproducing the tangle of a treetop is therefore difficult.
Computer learns from video
Motion capture usually uses markers on the body, which would be very difficult with trees. If no markers are used, it relies, among other things, on the knowledge that the skeletal structure of the human body is always the same. “Branches, by contrast, vary greatly even within one species of tree. The actual ‘skeleton’ of a tree is usually not recognisable at all because of the foliage,” Hall says. Nevertheless, the computer scientists have succeeded in developing software that uses video recordings of trees to learn how to create realistic animation models.
“Our software infers the wooden skeleton from the movement of leafy branches,” Hall explains. Using a single video, the system learns to make virtual trees “grow” so that they also differ slightly from one another. “Animators no longer have to draw or use complex interactions to create new trees,” the computer scientist emphasises. Thanks to statistical methods, the system avoids unnatural shapes when reconstructing trees in three dimensions.
To create genuinely different kinds of trees - such as oaks and birches - the software needs a video template for each genus. It can then create a mixed virtual forest. “All our trees move in the wind as they did in the original recording,” says Hall. The software generates the moving 3D models directly, whereas until now animators first had to add movement subsequently to initially static tree models.
Simple and fast
According to Hall, the software is very easy to use. “The user only has to draw the outline of the tree in one frame. Then it takes only one click to create a new tree,” says the computer scientist. Different wind strengths or seasons can be simulated. “Our system will make it faster and easier to create animated backgrounds,” Li believes.
Animation studio Aardman, known for “Wallace and Gromit”, has already expressed interest in the technology, which Hall says is also likely to be of interest to architects and game producers. “You could even use a mobile phone to create a personal animated tree that dances to the ringtone,” says the computer scientist. Li, meanwhile, emphasises that the technology is also intended subsequently to be used for other animations, such as clouds, water, fire or smoke.
