What Is "Digital Remastering"?

The process of turning classics into HD

the Blu-ray format stores and plays movies in high definition—easy for new flicks shot digitally in HD, but what about classics like Metropolis (due out on Blu-ray next year) that were shot on film? The trick is to make a small digital file without losing too much information in the process, which could yield a poor-quality image. Here's how it works.

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Step One

Remove dirt from the original film roll with ultrasonic waves and a liquid, and fill scratches with a special fluid to make them temporarily invisible.Steve Karp

Step Two

Put the film on a scanner to make a digital image of each frame. Scanning at 4,000 lines per frame is a good approximation of a 35-millimeter celluloid film.Steve Karp

Step Three

Scan each color channel—red, green and blue—four times to produce a vivid image, true to the film, which naturally captures color better than digital sensors.Steve Karp

Step Four

Edit the film frame-by-frame. Technicians manually correct for color discrepancies and remove blotches and other signs of age. This can take up to a year.Steve Karp

Step Five

Compress the digital file. The MPEG-4 compression often used in Blu-ray is better than other methods at creating a small file while preserving the original's detail. Instant Expert: Launch Your Quick and Easy Primer on Just About Everything at popsci.com/instantexpert.Steve Karp