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The second interesting challenge handed to the miniature photography crews was the different way Duboi extracts mattes. Duboi, which uses proprietary compositing software, works down a different path than most compositing teams. Henry explains: "The compositing process that they use to extract the mattes from our photography at Duboi is reminiscent of working on the Henry; they use a color difference system to pull mattes."

The Betty photographed motion control against a greenscreen. For more photos on the miniature set of ALIEN, visit General Lift's web site.
To develop this color difference photography for miniature ship shots, the miniature unit experimented and tested for a month, "to make sure everything would work correctly," Henry said. "This was important, since we needed to come up with the best combination of techniques to get all of our passes to work with Duboi's system. Could we just use a red screen? Can we use a greenscreen? We had to test everything."

In shooting for this color difference matte, Henry explains, "we placed a red screen behind the object that was exposed once on the film. The film was backwound, and the redscreen was turned off, and blue light was spilled all over the object in the foreground," giving a final print of blue against red, the color difference matte. Henry continued, "For the most part, that worked very well. It would eliminate the amount of spill on the foreground image, and that's what Duboi was most interested in. They simply could not use an object that was black--their color difference system doesn't see black."

Joe Lewis remarked about the process, "'Viva le differance!' I would shout to our French friends," he joked. "It was quite arduous. We got a beautiful matte from the process, no doubt about it. The grain would be very fine, with little or no noise, and it fit beautifully. It turned out quite nice."

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