Marrying IMAX and 35mm in The Dark Knight
Digital and Photochemical Blend Together
The conversation continued on The Prestige, when Imax lent Nolan an Imax camera and did the post for no charge. The two or three shots in “The Prestige” shot in Imax were then scanned at 8K, an extraction for 35mm’s aspect ratio was made and they were integrated into the film. “He proved it could work,” said Keighley.
These escalating experiments with integrating Imax footage into a 35mm film came to a head in “Dark Knight,” which incorporates 28 minutes of Imax footage. “Imax filmmakers have taken the cameras to Mt. Everest, to the Titanic at the bottom of the Atlantic Ocean, and in space,” said Keighley. “Great documentaries have been made. Chris said, How can I take this incredible medium and put it in a narrative Hollywood story. We’ve been waiting for this for 40 years.”
Posting Imax and integrating it with 35mm footage, for both an Imax and 35mm version, presented a lot of unknowns. “We did a lot of tests and we talked about how we could use the Imax format within the 35mm footage,” said Keighley. “We decided on doing straight cuts between the formats, and Chris decided to shoot anamorphic because it’s the biggest negative. And we started down the road.”
“In the post process, nobody had tried to integrate the two footages,” he continued. “Would it be weird to go from the one aspect ratio to the other? Chris and [editor] Lee Smith researched it carefully. We did 2.40:1 tests and put it on the Imax screen, cut between the two, and it worked. Artistically, they liked what it did.” The decision was made to use the Imax camera when the scene called for “more dynamic visuals.” The final film, reported Keighley, cuts between 2.40:1 and 1.33:1 more than a dozen times. “Sometimes it’s very evident, and sometimes you don’t even notice it,” said Keighley, who emphasized the testing Nolan did before he went forward. “His vision was correct.”
For the 35mm version of “Dark Knight,” Technicolor color timer David Orr handled the majority of the film as a photochemical finish. “The only part of it that was digital was anything derived from the Imax footage or digital effects,” said Keighley. To incorporate footage from the Imax frame, DKP 70mm first scanned the selected Imax takes at 8K resolution, using its Filmlight Northlight scanner, and then Nolan and his editor Smith took an “extraction,” or a portion of the image, based on the framing they choose. “It’s usually a center slice,” said Keighley, who confirmed that the Imax version of “Dark Knight” incorporates the footage cut out of the 35mm version of the film.
The Imax version, however, involved a much heavier digital hand, since all the 35mm footage went through Imax’s DMR process, in 4K. With regard to the Imax shots, any one that incorporated a visual effect was created as a DI; every Imax shot without a digital effect was timed photochemically. “We take the data from the DI, perhaps that’s 2K, and we up-res it and use out proprietary algorithm to de-grain,” said Keighley. “If it’s all digital, it’s a DI, usually at 4K. Out of the 2,000 plus shots, 200 were digital effects, so those were digital. But the Imax shots without visual effects-which were a significant amount-have no digital version.”
How time-consuming is it to go through this digital/photochemical pipeline? “The dual pipeline for Imax is developing,” said Keighley, who noted that, when he talks about the dual pipeline, he is not simply talking about photochemical and DI finishes, but about the digital projection of Imax. “But it absolutely worked out how we hoped it would. Chris’ vision has come to fruition.”
At the end of post production, Nolan expressed his desire to make all the prints from the original negative. “From discussing it, we knew it was impractical,” said Keighley. “With 65mm, you can only print at 120 feet a minute, and that’s slow. We print the DMR negatives at 240 feet a minute. Also, your negative is like tires on your car. You only get so much mileage. The movie has 135 prints, and to make that from the original negative, you’d probably scratch it eventually.”
The solution was an A and B roll process. The A roll contained all the 35mm negative and a dupe negative for the Imax footage, in a single roll, all cut together. Whenever the roll would arrive at Imax footage, the shutter closed, and the B roll, with the original negative, would roll for that sequence. That saved a huge amount of time, since the A roll passed at 240 feet a minute. “That was quite innovative,” said Keighley. “Nobody had done it before, and we were able to make a significant number of prints that way.” Keighley also noted that, because Imax is physically 3.7 times longer than 35mm film, the Imax version of “Dark Knight” is comprised of 45 reels in the Imax version, 25 of which have Imax footage in them.
At the end of this unusual post pipeline, said Keighley, he counted up “hundreds of surprises.” “You have to be committed,” he said. “Chris is a tough customer, and amazing. He has real talent and real technical talent. He doesn’t have a perfect eye, but it’s pretty close.”