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Macs Do Star Wars Dirty Work
bfl writes "The BBC is running a story about Lowry Digital Images and how they used 600 dual G5s and 400 TB of storage space to clean the dirt off of the old Star Wars reels, and upgrade the resolution to get them ready for their DVD release."
Movie dirt is a special kind of "noise" in images, from a statistical point of view. Thus special filters can be applied.
Apple has it on their own web site here.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
Can someone elaborate on how shot noise applies to optical systems, specifically, cinematography? Since the original source material is conventional 'analog' film, at what point is the noise introduced? How is it introduced?
Well, it's all explained in the article. And you've got half the answer yourself. But I'll try to explain further...
(Yes I realize that film is not a pure analog format; the resolution being limited by the grain size of the emulsion - but at the same time, it's not what we consider digital.)
Film grain itself is a noise component. Film grains are nothing more than crystals sensitive to a particular light wavelength. In commonly used 35mm film stocks, there are three layers of emulsion - one red, one green, one blue. Think of the grains as "pixels", although they're somewhat randomly distributed, they're not all of a uniform size, and they're not all uniformly sensitive to light. The end result is that the minute differences between adjacent grains makes them easily discernible on a theatrical-size screen, and somewhat visible on a large TV set. They appear as noise.
Optical effects also involve compositing several layers of film on top of each other. According to the article, the light saber scenes were the worst. I'd imagine at that time, shooting a light saber duel probably involved three layers of film; the master shot and one optical shot for each light saber. Obviously this triples your noise and also softens the image. It can also introduce color casts because the light is being altered through each layer of film.
As films age, chemical reactions also cause color shifts in the grains. This can lead to even more noise.
Films also get just plain dirty over time. The Star Wars negatives have been handled a lot, so they're probably dirtier than most. 35mm not being very big, when you blow it up onto a theater screen or even a TV set, a small layer of dust or tiny particles of dirt will add a lot of crud to the image.
The software they used to clean up these films apparently works by comparing each frame of film to the frame before and the frame after, to see what's picture information and what's noise (random noise will be easy for a computer to pick out, because it will not match at all from one frame to the next). It should have no problem removing both film grain and dirt, as well as other types of noise.
I'd imagine they must have manually isolated each individual edit in the film to reduce errors, but this wouldn't have been that big a deal in the grand scheme of things. There's probably only maybe a couple thousand cuts per film (assuming a high average of 5-10 cuts per minute), so it wouldn't take more than a couple days for one person to do this.