# How do they put the yellow line on the field during football games? **URL:** \ **Category:** Factual Questions\ **Created:** [September 24, 2002, 6:05pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484 "2002-09-24T18:05:04Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Athena](https://avatars.discourse-cdn.com/v4/letter/a/35a633/32.png) [@Athena](https://boards.straightdope.com/u/Athena)\ **Post date:** [September 24, 2002, 6:05pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/1 "2002-09-24T18:05:04Z")
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? ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [September 24, 2002, 6:14pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/2 "2002-09-24T18:14:51Z")
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. ---
**Author:** ![Delta-9](https://avatars.discourse-cdn.com/v4/letter/d/3be4f8/32.png) [@Delta-9](https://boards.straightdope.com/u/Delta-9)\ **Post date:** [September 24, 2002, 6:18pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/3 "2002-09-24T18:18:27Z")
I’m sure a tech-type will be along shortly, but IIRC, it’s done with smart software. ---
**Author:** ![Ins\_Outs\_What-have-yous](https://avatars.discourse-cdn.com/v4/letter/i/8797f3/32.png) [@Ins\_Outs\_What-have-yous](https://boards.straightdope.com/u/Ins_Outs_What-have-yous)\ **Post date:** [September 24, 2002, 6:20pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/4 "2002-09-24T18:20:26Z")
[link](http://ask.yahoo.com/ask/20001012.html) > [@](#): > > “There are eight computers… three sets of special encoders and abundant wiring dedicated to generating the virtual first down line in video format.” The virtual line is drawn on video based on the position first down marker, ridiculously exact details of of the live camera’s position (including altitude and lens angle), a digital 3D model of the field, and two palettes of colors for the field and the players. The player’s colors automatically override the virtual line’s colors, so it appears as though they’re stepping over it. ---
**Author:** ![Skammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skammer/32/143_2.png) [@Skammer](https://boards.straightdope.com/u/Skammer)\ **Post date:** [September 24, 2002, 7:11pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/5 "2002-09-24T19:11:33Z")
An excellent [article](http://www.howstuffworks.com/first-down-line.htm) describing the process, courtesy of [HowStuffWorks.com](http://HowStuffWorks.com) ---
**Author:** ![Mars\_Horizon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mars_horizon/32/2804_2.png) [@Mars\_Horizon](https://boards.straightdope.com/u/Mars_Horizon)\ **Post date:** [September 24, 2002, 7:33pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/6 "2002-09-24T19:33:57Z")
IMHO, this would make an excellent Staff report or even (gasp!) Column by The Master. ---
**Author:** ![xizor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xizor/32/102_2.png) [@xizor](https://boards.straightdope.com/u/xizor)\ **Post date:** [September 24, 2002, 7:36pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/7 "2002-09-24T19:36:25Z")
[Here](http://www.dtvprofessional.com/cgi-bin/getframeletter.cgi?/2002/09_sep/features/cw_pvipete.htm) is a very detailed description of how they do it. ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [September 24, 2002, 8:46pm UTC](https://boards.straightdope.com/t/how-do-they-put-the-yellow-line-on-the-field-during-football-games/129484/8 "2002-09-24T20:46:50Z")
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”.