Dark Knight Director Shuns Digital Effects for the Real Thing — but not totally:
“So we got an Imax shot of Christian Bale as Batman standing on top of the Sears Tower,” Pfister says. “Here we are with our principal actor standing on the edge of one of the tallest buildings in the world. I think a lot of people will assume that’s CGI.” Perhaps, but when you see the shot (featured in the first trailer), your eye instinctively detects something different, something thrilling and rare: photographic reality.Settling for anything less, Nolan feared, would send the Batman franchise back into camp and mummery. That’s why he transported his hero to the very real city of Hong Kong. Unfortunately, the real world has its drawbacks. “The Chinese government was a nightmare in terms of filming stuff,” Pfister sighs. “They wanted to limit the amount of helicopter activity over the city.”
And Nolan needed helicopters. He especially wanted to minimize digital meddling in those high-altitude Imax sequences. His reasons were both aesthetic and practical: Imax film stock is enormous, roughly 10 times the size of 35-mm celluloid, and it soaks up a vast amount of visual information. Those dimensions are what make the image so rich and sharp, even spread over a screen the size of a blimp hangar. While conventional films are digitized at 2K resolution (2,000 pixels across), or 4K at most, adding visual effects to Imax footage requires digitizing each frame at up to 8K. In other words, the difficulty and expense of doing f/x rise exponentially with the size of the negative.
If I may geek out here for a moment — math-geek out, that is — the expense of doing f/x should rise polynomially — quadratically, in fact — with the (linear) size of the negative. An image with twice as many pixels across should have four times as many pixels total — two squared.
What? Why are you looking at me like that?