# The First Down Indicator on TV Football Games **URL:** \ **Category:** Factual Questions\ **Created:** [October 24, 1999, 7:19pm UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211 "1999-10-24T19:19:00Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Torgo](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@Torgo](https://boards.straightdope.com/u/Torgo)\ **Post date:** [October 24, 1999, 7:19pm UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/1 "1999-10-24T19:19:00Z")
I’m referring to the yellow line FOX-TV uses in the broadcast of their NFL games. It’s obviously electronically imposed but I can’t figure out exactly how they do it. For one thing I’ve noticed that it seems to be used in such a way so that the players can be seen stepping over it, instead of having the line “keyed” over the entire picture. Are there any TV engineering types out there who can give a clue? * * * Tim “My hovercraft is full of eels.” ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [October 24, 1999, 9:43pm UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/2 "1999-10-24T21:43:00Z")
They’re ALL doing it now: ABC, ESPN and CBS. I don’t think NBC is doing it because the only football they show now is Notre Dame home games and a couple of New Year’s Day games. I don’t know how it’s done, but I remember when it was introduced last year on ESPN (they were first), they said it was expensive and would only be used on national telecasts. Maybe it got cheaper. BTW, have you noticed the line sometimes disappears when it “crosses” a shadow? * * * Those who do not learn from the past are condemned to relive it. Georges Santayana ---
**Author:** ![Hunsecker](https://avatars.discourse-cdn.com/v4/letter/h/d78d45/32.png) [@Hunsecker](https://boards.straightdope.com/u/Hunsecker)\ **Post date:** [October 24, 1999, 10:55pm UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/3 "1999-10-24T22:55:00Z")
Well, heres my WAG for how it works: The trick would be knowing exactly where the camera is, and where it’s pointing. Maybe focal length too, but I don’t know about that. Once you know that, you can find out where, in the cameras view, the 1st down markers ought to be. Then along the line between the markers, just replace the green of the field with yellow. Thats why it doesn’t work well with shadows, crossing the logo at the 50, etc. I saw some very cool demos of similar technology that UNC-Chapel Hill is working on called Augmented Reality. One page on it is here: [http://www.cs.unc.edu/~azuma/azuma\_AR.html](http://www.cs.unc.edu/~azuma/azuma_AR.html) They use head mounted displays and half silvered mirrors rather than cameras and computer composition, but the principles are probably the same. ---
**Author:** ![aseymayo](https://avatars.discourse-cdn.com/v4/letter/a/a88e57/32.png) [@aseymayo](https://boards.straightdope.com/u/aseymayo)\ **Post date:** [October 25, 1999, 12:54am UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/4 "1999-10-25T00:54:00Z")
Augmented reality - oh, I want that! ---
**Author:** ![Troy\_McClure\_SF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troy_mcclure_sf/32/4150_2.png) [@Troy\_McClure\_SF](https://boards.straightdope.com/u/Troy_McClure_SF)\ **Post date:** [October 25, 1999, 4:39am UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/5 "1999-10-25T04:39:00Z")
It’s so consistent and non-wavering. Wow. Reminds me of something Fox Sports Net-Bay Area (and probably oodles of other stations) uses. It’s called either ELVIS or L-VIS, I forget which one. It’s used to “project” an advertisement onto the panels behind home plate in the basic centerfield camera shots. The panel isn’t treated with anything, and I’ll bet anything its pretty much the exact same technology as the down line. Whenever a gust of wind blows, it causes what looks like a shadow, and when a lefty steps out, he casts a shadow, too, a little bigger than the player’s image. * * * JMcC, San Francisco [http://members.tripod.com/~weirdstuff/index.html](http://members.tripod.com/~weirdstuff/index.html) “Hear the voices in my head, I swear to God it sounds like they’re snoring” ---
**Author:** ![zuma](https://avatars.discourse-cdn.com/v4/letter/z/e9c0ed/32.png) [@zuma](https://boards.straightdope.com/u/zuma)\ **Post date:** [October 25, 1999, 5:05am UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/6 "1999-10-25T05:05:00Z")
[howstuffworks.com](http://howstuffworks.com) covered this very question a few weeks ago… [http://www.howstuffworks.com/question225.htm](http://www.howstuffworks.com/question225.htm) ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [October 26, 1999, 2:32am UTC](https://boards.straightdope.com/t/the-first-down-indicator-on-tv-football-games/4211/7 "1999-10-26T02:32:00Z")
Well that certainly answers it. * * * Those who do not learn from the past are condemned to relive it. Georges Santayana