Hallet's presence in the attic is a direct challenge to the newly freed Jimmy, who shimmers with a diffused quality as he circles the detective. The interaction needed to make the scene work drove Riddle to shoot the two actors against greenscreen in the confined attic set using motion control. "Originally, we weren't going to shoot any motion control," Riddle admits. "But it was important in a performance sense to have the actors connect with each other, and we realized that if we just did all the shots as lock-offs or with added post moves, it really wasn't going to play. We pulled in motion control strictly for a couple days and kept it simple - pan-and-tilt stuff only. Once we knew exactly what the pans were, we just tacked the greenscreen to the walls of the set and lit it to get separation between the actors and the background. Then we went back to our original set lighting and shot the empty set via motion control to match it, so we could put them back into the plates later. This allowed Griffin to use the same space, get the performances he wanted and get the essential backgrounds that were needed."
This strategy was particularly helpful with regard to a remarkable moment when Jimmy pushes Hallet and his hand literally penetrates the detective's chest. "In the original greenscreen plate, Goron moved his hand forward, grabbed Aidan's chest with his open palm and pushed him back a bit," Riddle remembers. "Because the two actors were actually shot together, you feel the physical impact and you see it in Aidan's clothes, which shake a little bit. We just painted away all the contact of Goron's hand with Aidan's chest, replaced the clothes, put a little wrinkle around there and created a matte, so it would look as if the hand went right in."
An instant later, Jimmy yanks out his hand and stares at the imprint of Hallet's five-pointed badge burned into his palm. Realizing the power of his badge/talisman, the detective points it at Jimmy, who rapidly disintegrates. Jimmy's spectacular destruction is the result of a new proprietary technique that Cinesite has dubbed Optical Flow. This remarkable program correlates the positions of thousands of individual pixels from one frame to the next, then applies that data to an unrelated series of frames to create perfectly synched effects on the most minute level, like using an explosion to drive the destruction of Jimmy's body. "If Goron turned his head," Riddle posits, "the program showed us which direction each pixel was moving in, and at what velocity. Once we have that type of information, we can simply apply the data to a totally different sequence of images and have the movement of the original set of images drive the second set of images."
In this case, Riddle's crew shot a large-scale pyro-effect, analyzed its movement using Optical Flow, then applied that explosive motion data to Visnick's image. The result is a disintegration that explodes the actor's body into minute fragments with far greater naturalism than straight particle systems, which tend to look too mathematically precise. The process was also far less labor-intensive than trying to animate an organic explosion. Riddle explains, "This is more of a 2-D technique, but unless you're willing to spend lots of time animating it and lots of processor time rendering it, there's no 3-D approach that can create the real, organic quality that something as simple as a little puff of smoke can give you. For the sequence in question, we analyzed the movement of the explosion to see how it changed from one frame to the next, and then applied that to Goron's image and exploded him apart in a way that looks very natural and intricate. It's quite CPU-intensive, but it depends on how fine a detail you want. The rougher you can live with a particular shot, the faster you can get it done, but it typically takes five to 10 minutes per frame. The method certainly has its limitations, but it gave us a lot more for a lot less effort than in the past."
Other changes were made to Jimmy's appearance to shift the film's dark tone back toward the comedic. "Griffin wanted to turn this moment, which could have been very tense, on its ear and make it comical," Riddle relates. "Once Jimmy was exorcised, we originally thought that we were just going to make a liquidy thing or a big mass of hornets flying around in roughly Jimmy's shape. We figured we didn't need to shoot anything with Goron; we'd just be able to model him with stills, because this mass of swirling stuff didn't really need to have his image on it. Then Griffin decided he wanted to see Goron in the scene, which became an interesting 3-D challenge. That evolved over a short period of time, from a big gelatinous mass that was flung up on the ceiling to a desaturated version of Goron hovering on the ceiling in a cloud of swirling dust made of what we call 'bits.' We shot Goron hanging on wires against a greenscreen, with no proximity to any kind of ceiling. The set itself had no ceiling, so we created that element and added a drop shadow so Goron looked as if he was hanging a little bit below it."
For Jimmy's ultimate demise, Dunne once again changed the original scenario in favor of humor. Where the original ending called for the evil spirit to make a final death-defying leap into his grave and disintegrate in mid-air, the revised climax called for a more active approach, wherein the heroines pour a big cauldron of witch's brew over Jimmy's midsection - with predictable results. "He's like the Wicked Witch in The Wizard of Oz," Riddle grins. "Jimmy melts down into the ground with this terrible expression on his face, and all that's left are his boots! We did that using a combination of the 2-D Optical Flow to analyze his movement over several frames, plus 3-D tracking to match-move our 3-D Goron model to his movements, so we could disturb his image as it was going through the ground plane. He's melting from the middle of his body, and his head and legs sink into the ground at the same time. We therefore added some steam and stuff where his body intersects the ground, then created an effect to make him look as if he was just dissolving away."
As fun as the onscreen antics appear, putting the digital-effects magic in Practical Magic was not always so carefree and fun. "You know, I could easily say that it was a nightmare show to work on, but I try to put a good spin on it," Riddle sighs. "I think we managed to create an environment that allowed the director to make a lot of late creative decisions. We were able to roll with the punches so Griffin could change the ending of the movie, and we still produced something great by the original deadline. It's a powerful thing to be able to say, 'We can still work this late in the game,' but I'm not necessarily excited about having people know about it!"
