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for The Prince of Egypt
by Ron Magid
The two princes of Egypt, Ramses and Moses, race through the city on chariots with some added help from DreamWorks' new Exposure software, which facilitates 3-D perspective changes.
Beginning with Disney's Beauty and the Beast in 1991, the computer graphics revolution has had a significant impact on traditionally animated motion pictures. While CGI has produced imagery that would be nearly impossible to achieve with traditional techniques, the infusion of three-dimensional animation and parallax into a two-dimensional universe can be somewhat jarring to the viewer's eye. On the technical end, 3-D animation is much less forgiving than 2-D: animators are forced to work within the 3-D environment's parameters rather than being able to follow the dictates of drama. Essentially, animators needed a system that would enable them to compose and recompose shots like real cinematographers, then translate any camera moves from the characters to the backgrounds and vice-versa in essence, a motion-control system for animation. DreamWorks SKG has devised just such a system dubbed Exposure for its animated Biblical epic The Prince of Egypt.
Previously, if animators wanted to incorporate three-dimensional CG imagery in animated films, the 3-D background elements complete with camera moves had to be created first, with the traditional animation choreographed through the environment afterwards. But DreamWorks co-founder Steven Spielberg didn't want the film's characters to be subservient to their surroundings, particularly in such key sequences as a breathless chariot race between Moses and Ramses through streets and around palaces. "Steven wanted a very active camera, one that was submerged in the environment, which is very difficult to achieve in 2-D animation," explains The Prince of Egypt's scene-planning supervisor, Dave Morehead. "So we said, 'Okay, if we're going to do that, we want a full 3-D environment.' Now, the solution to that is to create a 'live-action set' in the computer, and put our characters in there, which is exactly what Steven specified. But up until now, that approach has been very limiting, because we couldn't change our camera moves after the fact. Suppose I put my 3-D chariot in this world, do a camera move around it and everything looks great. The animators, being who they are, probably decide that they will want a character to stand up and crack a whip halfway through the shot, which means that the character will go out of the top of the frame."
Before the introduction of Exposure, the animators would have been forced them to confine the character's actions to the background's boundaries. "Exposure allows us to go with 2-D animation first or 3-D animation first, depending on which should lead artistically," says Morehead. "In the chariot race, we wanted the 2-D horses to seem as if they were pulling the 3-D chariot, so the 2-D animator would start off by drawing a rough horse and a rough chariot. We'd format those drawings so that the 3-D animators could work with them in that environment. Then, we'd plot out the chariot's movement, relative to the horse drawing, and the 2-D artists would go in and draw the driver. At the same time because Exposure allows us to simultaneously maintain both sets of data discretely and choreograph them separately we always maintained the possibility that we could change the camera move or the animation, within reason, throughout the process."
Exposure is the latest in a long line of software camera packages designed to bridge the 2-D and 3-D realms. Previous incarnations never quite addressed all of the problems faced by animators moving between the dimensions. "I've worked on three other systems that tried to solve this problem, but we never went the whole hog," Morehead admits. "We tried just to bite off little plug-ins in Alias, and an interpreter for the 2-D package we were working on. This time, we said 'To hell with it,' and decided to build a fully integrated package to allow the animation scene-planners to work a little bit more like live-action directors of photography. We're essentially the cinematographers, and it's our primary responsibility to handle the integration between all of the 2-D and 3-D elements. Up until now, the choreography of those 3-D and 2-D worlds has been kind of difficult. 3-D packages like Alias and SoftImage are great for working in 3-D environments, but they don't really lend themselves to the flat 2-D world. What we wanted was a tool that would combine the strengths of both worlds, and allow us to conveniently choreograph all of these 2-D and 3-D elements in one interface.
"Now, if we want to animate Moses sitting in a chariot, we can animate Moses and then use Exposure to bring that into [Cambridge Animation Systems'] Animo our 2-D animation package along with an Alias wire file of the chariot. We then choreograph them both and put a camera move around them. That way, the two individual packages are doing what they do best Alias deals with 3-D objects, and Animo does all of the 2-D work. Thanks to Exposure, the traditional animators could get the 3-D elements from Alias onto paper, and the Alias animators could have all of the drawings in the shot in the 3-D world. Exposure started off as a choreography tool, but turned into a sort of 'translator.' And it's not just a one-time translation it's an ongoing communication between the 3-D, 2-D digital and paper worlds, which allows us to pull in the best features that each component has to offer. But we don't actually composite the elements in Exposure instead, it acts as the choreography tool, sending instructions back to the individual packages as to where to put the cameras and how to move each object in the scene so they all lock together. Then the compositing of all the elements is done in Animo."
The Prince of Egypt's sceneplanning supervisor, Dave Morehead, "In the chariot race, we wanted the 2-D horses to seem as if they were pulling the 3-D chariot, so the 2-D animator would start off by drawing a rough chariot. Then we'd format those drawings so that the 3-D animators could work them in that environment."
With Exposure, the virtual camera rotates around the 3-D chariots as it's also rotating at the same speed around the "billboards," flat cutouts of the characters in the chariots over which the artists animate. "Through Exposure, we can assign behaviors to the billboards that the characters are on," Morehead reveals. "Before, when we'd do all of the 3-D elements first, and then animate the character to it, we'd have to re-draw the character in a different position every time that 3-D object moved. But in Exposure, we have all the common 3-D properties, like being able to 'parent' one object to another object, which means that we can actually put a billboard inside a chariot and parent it, so when we move the chariot around, the billboard goes with it. That way, the character doesn't have to be animated every time the camera moves, which is a distinct advantage."
"Then, we lock a 'plot camera' to the billboard to print out each frame of the chariot on 11" by 17" paper, translating the perspective of the 3-D object onto the billboard itself. For example, that gives us a full 360-degree move around a chariot in 3-D; when that's plotted out, the character animator sees the chariot revolving completely and can actually animate that revolve to his character," adds Morehead. "Then we'll take their drawings and scan those back into the computer."
Animators can also employ this technique to create the illusion of growing size as a character rides from the distance into close-up. "Most of the animation is not really done in perspective, per se," Morehead says. "For a scene of the chariot flying down the street, the animator might be looking at the chariot from the same perspective the whole time. We can use the plot camera to extract out all the translation movement, rather than drawing the character small when he's far away and large when he gets closer. That way, the chariot pretty much stays the same size and the animators animate a constant-size image. It's a significant advantage not just in look, but cost as well because we don't have to re-animate that character every time the chariot moves."
But if this powerful tool primarily handles choreography of the 2-D and 3-D elements, why the name Exposure, which conjures images of a lighting tool? "It does everything but the lighting," concedes Morehead. "We didn't actually pick the name, the developers picked it. To me, it doesn't matter what you call it, except that people are always asking me, 'Oh, now show me the Exposure portion,' and I have to explain, 'Well, it does choreography.'"
Although Exposure does not affect the lighting of a 3-D scene, it has enabled real-world background painters to translate their 2-D work into 3-D, with remarkable results. "After we've built a 3-D set, we'll print a specific angle out, which becomes a template that the background painter physically paints using oils," Morehead says. "Then we scan the painting and project that image onto the 3-D geometry. The Exposure tool extends the painting into the room and gives us parallax on all the objects. Therefore, what we got when we rendered the images were actual paintings in 3-D, instead of 3-D lighting. We used very little 3-D lighting in rendering."
As with a masterful painting, DreamWorks' artists relied on different shades to convey the sense of lighting. Despite the fact that no computer can quite match the rich patina of oil paints, Exposure enabled animators to place their characters in totally hand-painted 3-D landscapes. The end result is that The Prince of Egypt resembles a canvas in motion. "These backgrounds are literal paintings, and the same background artist also painted whatever 3-D props and objects are in the shot," claims Morehead. "I know that other companies care trying to develop a system that allows artists to paint directly on the computer, but artists will always want to use real paints. We wanted to make sure that our background artists who are trained in oils and have painted that way for 20 years could contribute significantly to the look of the film."
Best of all, The Prince of Egypt's spectacular visuals are merely the "tip of the proverbial pyramid" in terms of what Exposure can deliver to the screen. "Many of the scenes in The Prince of Egypt were started before we had a working version of Exposure," says Morehead. "A lot of the software was rapidly prototyped, so we kept going back in and ironing out problems. We're still working on it even today, making things quicker and cooler. But it's done everything we'd hoped it could do and more. We used Exposure for 178 shots in The Prince of Egypt. So far, our next animated feature, El Dorado, has somewhere around 350 Exposure shots, and we're only about halfway through the production."
This new technology may have even greater resonance in the domain of live-action moviemaking. "Anybody who is faced with integrating 3-D CG into their film is going to have exactly the same problems that we encounter," opines Morehead. "I suspect that in the very near future, live-action directors are going to be using tools very similar to Exposure to integrate 3-D and live-action, so look for a tool like this on your shelf in the next couple years."
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© 1999 ASC