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Two guys, one of them not exactly a rabid football fan, go to the Meadowlands for a late-season Jets game. With things barely underway, our unlearned fan turns to his friend and asks, "Where's the stripe?"
His buddy looks perplexed. "What stripe?"
"Y'know. The stripe. The first-down stripe."
He means, of course, that electronically generated stripe that turned up on TV this year, the one that shows you how far the offense needs to go to make a first down.
ESPN introduced the stripe in a 27 September telecast between the Cincinnati Bengals and Baltimore Ravens in Baltimore. So this is a new wrinkle, meaning the technology is a Super Bowl rookie this season. But it will be there, says Fox Sports, which will broadcast Super Bowl XXXIII from Miami.
On 31 January, TV viewers will see a thin, colored line across the field showing not down, but distance. Various incarnations of the technology go by different names, including the "First and Ten" and "First-Down."
"From sideline to sideline at the first-down marker, [viewers] will see a thin line running across the field that will instantly let them know whether or not a runner or receiver has made first-down yardage," said Fox spokesman Lou Dermilio.
Fox even hopes to introduce the stripe in time for the National Football Conference championship game.
CBS, which broadcasts AFC games, deployed the stripe earlier this season and ABC, which owns ESPN, used it on Monday Night Football. Fox is working to finalize a deal with one of the two companies that provide the service: Princeton Video Imaging and SporTVision.
The innovation is only a simple stripe, but the result belies the underlying technology.
"The applications of existing technology in this format did not exist prior to this season," said Dermilio. "You could have drawn a line across the field, but that would have messed up the field. This gives the viewer a visual aid without scarring the field."
The marker almost appears as though it was painted on the field along with the yard lines. Players walk over it, and it remains stationary relative to the field -- not moving with the camera as other on-screen graphics do. Broadcasters consider it critical that the line not obscure the many moving on-field objects it intersects: players, a flying ball, helmets, and the occasional pigeon -- all while it is painted into live video frames at a rate of 30 times per second.
"That's why it's been accepted so quickly -- it's unobtrusive," Dermilio said.
The job requires a trailer-full of Silicon Graphics workstations and four technicians parked outside the stadium, said SporTVision chief operating officer Jerry Gepner.
A 3-D representation of the field in question -- be it 3Com Park in San Francisco or the Meadowlands in New Jersey -- is at the center of the computer work. Each field has unique characteristics that set it apart from all others. These differences must be incorporated into the digital representation so the computers can generate a stripe that will lay perfectly across the field. Building that 3-D model requires surveying and measuring lines, slopes, graphics, and other distinguishing characteristics of the field.
The other half of the technology involves overlaying the stripe generated by the 3-D model onto the video frames spewing from the camera. That image is anything but a simple grid pattern. It is skewed by camera angles, lens distortion, and motion.
To understand that image accurately, enhanced cameras send real-time data to the computers in the trailer, revealing their current pan, tilt, zoom, and more. The result is that the computer can tell exactly what the camera sees at any one moment.
The computers create a parallel camera view of the 3-D version of the field and use it to paint the stripe with the correct characteristics. The stripe is extracted and merged with outgoing video frames -- and the viewer barely notices a thing.
Finally, the stripe has to learn to distinguish grass -- or Astroturf -- from the rest of the content of a video frame. It mustn't draw over players, on-field graphics, or the ball itself. That's where manual intervention meets automation. The computers learn to automatically determine which patterns of color, hue, and saturation are the green of grass -- or in some cases the brown of dirt. Thus the white of a player's uniform appears to be "on top" of the line.
But if conditions change during the course of the game -- due to weather, sunlight, or a worn-down field -- technicians show the computer new excerpts to exclude the stripe from. A Kansas City game broadcast by ESPN earlier this season was suspended for rain, and when play resumed a giant puddle lay over the field. SporTVision technicians "sampled" the puddle and instructed the computers not to draw the line over the puddle. They felt it would look too unrealistic.
Though the technology is sophisticated, Gepner said "the bigger trick was developing a clean user interface for this." The interface had to let technicians quickly work with images and easily select and sample excluded content.
"We think it's definitely an enhancement that serves as an aid to the viewer. And, ultimately, the goal is for all our technological enhancement to improve the viewer's experience," said Dermilio.
