Fox's hi-def slo-mo solution
R&D engineers slow down the action with high-speed camera and HD disc recorder
By Michael Grotticelli -- Broadcasting & Cable, 10/14/2001 8:00:00 PM
Engineers at the News Technology Group, the R&D arm of Fox Television in Los Angeles, say they have figured out a way to produce high-quality slow-motion images in high definition.
Using a Panasonic 720-line, progressive-scan, variable-speed HD camera (the HDC-27V) and the HD Station, an all-format HD disc recorder made by Germany-based DVS, they capture images at a faster frame rate than normal, 60 frames per second as opposed to 30 or 24, and then slow the footage down during playback from the disc recorder to produce the slow-motion effect.
"The HDC-27V and the DVS HD Station produce excellent slow motion," says Jim DeFilippis, vice president, television engineering for the group.
Fox Television has used the system for slow-motion (and fast-motion) effects in sitcoms Titus and The Bernie Mac Show, both shot on HD video. Fox Sports has also been experimenting with the system.
"We're trying to get as much out of existing equipment as we can," says DeFilippis. "Progressive scan makes the video look film-like. It enhances the quality and provides better motion capture."
TV producers have to struggle to come up with good HD slow-motion. According to DeFilippis, it's difficult to run the 1080-line interlace-scanning cameras at the high frame rates needed for slow motion and still produce good-quality images.
"Right now, it's technically not possible because of all the information that's needed to fill a 1080 interlace picture," says Ken Aagaard, vice president of technology, CBS Sports. "As far as we know, it can't be done."
To get a little slow motion into its 1080i HD football broadcasts, CBS is shooting the slow motion in standard-definition and upconverting to HD.
The News Technology Group's slow-motion system derives from post-production work it did three years ago, transferring 35mm film to 1080 progressive-scan, 24-f/s HD, DeFilippis says. The film was run through a telecine at 30 f/s (instead of film's normal 24 f/s). To get back to 24 f/s, technicians had DVS design a special disc recorder that would play back the 30-f/s material at 24 f/s.
For the two sitcoms, DeFilippis says, footage was recorded at 60 f/s and played back at 24 f/s. The DVS recorder adds a 3:2 "pulldown sequence" (alternating playback of three repeat frames and then two repeat frames) to provide clean and smooth slow motion.
DeFilippis picked the DVS recorder because it can switch frame rates "on the fly," he said. "With the disc recorders available [in the U.S.], you have to choose a frame rate and stay on it. The ability to change rates immediately gives producers more latitude."
DeFilippis says his group is waiting for the prototype Philips LDK-7000 camera from Thomson, which can capture images up to 72 f/s. It promises even better slow motion, he says, noting that the higher the capture frame rate, the smoother the slow motion. (Thomson's LDK 23, a digital super-slow-motion camera system for standard-definition digital, captures images at 90 f/s.)
For sports applications, for which portability of the recorder is important, the group may be able to use the Panasonic HDC-150 digital VTR, DeFilippis says. It is able to play back video at variable speeds up to 60 f/s.
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