How do they put the yellow line on the field during football games?

Y’know, that yellow line that appears on the field that indicates where the ball needs to get to for a down. It looks just like it’s painted on the field, the players step on it, the ball bounces over it, etc. etc. But we all know it’s fake. What’s the technology behind it?

Seems like if they just painted it across the screen that they’d have problems when a player or the ball crosses it. Mr. Athena postulated that they have a couple of guys down on the field that move markers that beam some sort of beam across the field, and the cameras pick it up as a yellow line.

So how do they do it?

It’s a matte. The line is computer-generated on one video source, and the game is displayed on another. The matte is keyed to the green color of the field, so when the green is blocked, the line is not displayed in that spot.

I’m sure a tech-type will be along shortly, but IIRC, it’s done with smart software.


An excellent article describing the process, courtesy of

IMHO, this would make an excellent Staff report or even (gasp!) Column by The Master.

Here is a very detailed description of how they do it.

They first tried using this basic technology in hockey, to make a “glowing puck” that was much easier to see on the TV screen. I liked the idea a lot, but most people didn’t, so it was dropped. When the Carolina Hurricanes were being introduced to central North Carolina, I actually heard one confused guy call in to the local sports station to ask if the players “found the puck’s glow to be distracting”.