Digital Intermediate: The Best thing since Acetate
Although not a cutting edge technology, Digital Intermediate, or DI, has begun a new revolution in the movie industry.
The technology behind DI is incredibly complex, but the idea is simple. Take a 35mm negative, scan it, manipulate the image digitally (the Digital Intermediate part from which the process gathers its name), and then burn this new digitally enhanced image to whatever media you need. The process has been used as a color correction and editing tool for many recent releases. “Oh Brother, Where Art Thou?” used it to produce the aged tint of the entire film.
Traditionally, DI technology has been an expensive and timely process for any production house, but recent improvements have dropped both of these factors significantly, opening the door for DI to become the de-facto standard for post-production editing.
How does it work? The process is similar to digitally enhancing photography. Scan an image, edit it, crop it, color enhance it, then save it. In traditional systems, each frame is saved to one of two standards, refereed to either 2K or 4K. People savvy with digital editing will immediately recognize this as a representation of the size and resolution of the scanned image.
Given perfect optics and grain selection, a print negative of 35mm film would correspond to a 6K image. For most DI prints, a 2K image is utilized, producing 2,048 pixels horizontally to 1,556 pixel vertically for frame image. A more expensive alternative, the 4K size, produces an image that is 4,096 pixels horizontally and 3,112 pixels vertically, but is also substantially larger. A 2K frame is about 13 MB, whereas a 4K frame is 52MB.
With traditional systems, the time to scan and then output to media was the budget killer for DI. These systems would take up to 12 seconds to scan each frame. Now this many not sound like much, but keep in mind that 35mm projectors feed film at 24 frames a second. That is 1440 frames a minute. A 90-minute film will have about 129,600 frames. That is 1,555,200 seconds to scan a 90-minute film