Mystery Solved: the yellow first down line
First down, no yellow feet
If you watch football on TV, you’re familiar with the first down line that appears on the field as the players are running around. It’s usually a bright yellow line that moves with each play, and it’s pretty obvious that it’s not really on the field but is superimposed for TV broadcast. I figured it was just some simple overlay done in the TV studio. Then one day, I happened to stop on a game while flipping through the channels and noticed that when a player walked across the line, his feet didn’t turn yellow. In fact, the line never once encroached on any solid item that crossed it.
A lot goes into that line
It turns out that adding the first down line to your TV screen takes an incredible amount of human labor and technology. It’s actually created by a company called Sportvision, and they use a tractor trailer full of equipment—including eight computers and at least four operators—to make it happen. The system needs an incredible amount of data and needs to solve a number of problems:
- It needs to know the orientation of the field in relation to the TV camera covering the field so that the line can be “painted” with the correct perspective;
- The system needs to be able to detect camera movements, including pans, zooms and focusing;
- It has to be powerful enough to refresh the line 30 times a second to keep up with your TV’s refresh rate;
- It has to be able to tell when players, referees and flags cross the line.
And that’s not even the half of it. Key to the process are special camera mounts that detect the movements and digitize them, as well as a computerized 3D model of the football field that helps the system account for crests and irregularities in the field. Equally important is a color palette built into the computer system. This helps the computers recognize when something that’s a different color than the underlying grass crosses the line.
The geeks behind the game
When a game is in progress, the Sportvision system collects all of the data from the camera mounts and then combines that with the data from the 3D map and the color information in the video feed. Two people, a spotter and an operator, manually enter the correct yard line information into the system. The spotter sits in the press box, and the operator sits in the production trailer. Two other people in the trailer work to make any manual changes necessary, including adding colors to the computer’s palette. This usually happens due to changing field conditions, including snow and mud. Once all of this information is collected and combined, the yellow line finally appears on your TV.
So this Sunday, when you’re sitting down on the couch watching your favorite team win (or lose), give a shout-out to the four guys putting in the hard work to make sure your favorite player’s foot doesn’t turn yellow when he crosses that first down line. They’re the geeks behind the game.
Article by Matthew West - Circuit City Life - September 2009
