How the Digital Lines on a Televised NFL Game Work

Today I found out how the lines projected on the field during a televised football game work.

What is happening behind the scenes of this seemingly simple line projection is actually quite complex.  Putting that yellow line across your television screen to mark a first down or a blue line to mark the line of scrimmage requires numerous technicians, 3-D mapping of every NFL field, copious amounts of sensors, eight computers, at least four people, and, according to Fox broadcasting, approximately $25,000 per game!

To get a better understanding of just how this is done, let’s start by looking at the problems that have to be solved. No NFL field is exactly the same. All fields are contoured to allow for water drain-off.  As such, every field has its own unique shape. Because the lines are computer generated, making a 3-D map of the football field that the computer can recognize is necessary.  The computer then has to know the orientation of the field with respect to camera positions. This allows the line to show up in the correct perspective based on where every yard line is. Because that same camera moves, the system has to be able to sense the movement and understand how to change where the line is based on the camera orientation.  Further, due to the fact that the game is filmed by several different cameras at different places in the stadium, the system has to do all of the work for multiple cameras at the same time. The system must also be able to sense when players, referees, or any object other than the field, crosses the yellow line, so it doesn’t paint the line over the top of them. Finally, the system must also be aware of any overladen graphics that the network might impose on the screen.

To solve all of these problems, technicians start with a special camera mount that records all of the camera’s movements such as zoom, focus, and tilt. This information is then fed to the computer so it knows what each camera is doing in real-time. Further, before the game starts, technicians make the needed digital 3-D model of the field being broadcast. Since all the camera locations are known by the computer. It can then take the 3-D model of the field, the locations and actions of the cameras, and orient the first-down line accordingly.

The ability to show the yellow line on the field and not on anyone or anything that it crosses is another matter altogether. This is accomplished by using layers of color. The technicians input different color layers into the computer before each game. One layer usually has colors like the greens and browns of the field. These colors will automatically be converted to yellow when and where the technician draws the yellow line. A cornucopia of other colors that could show up on the line (things like the players and officials’ uniforms, shoes, flesh, the ball itself, or any overladen graphics) are added into a separate visual layer. If any color other than the calibrated greens and browns get in the way of the yellow line, those colors remain and the yellow line disappears.

During the game, the computer continually analyzes all this information to decide where the yellow line should go, feeding the data to a linear keyer to superimpose the line onto the appropriate pixels in the video and refreshing it at an astounding 60 times per second. Walla! Every drunken football fan at home can now easily see where the 1st down line is!

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Bonus Facts:

  • European football was actually more popularly called “Soccer” in its early days due to the fact that “football” was a generic name for many sports at the time, such as “Rugby Football”.  In fact, the sport being referred to as “Soccer” preceded the first recorded instance of it being called by the singular word “Football” by about 18 years.  At that time, the sport was officially named “Association Football”, to distinguish it from the myriad of other “football” sports.  British school boys of the day liked to nickname everything, which is still somewhat common.  They also liked to add the ending “er” to these nicknames.  Thus, Rugby was, at that time, popularly called “Rugger”.  Similarly, Association Football was much more commonly known as “Assoccer”, which quickly just became “Soccer” and sometimes “Soccer Football”.  Click here for more on the origin of the word “soccer”.
  • Just as intriguing, for those who like to lambaste American Football being called such when the ball interacts primarily with hands, most of the earliest forms of Football were named thus, not because you kicked a ball with your foot, but because they were played on foot.   Peasants played most of their sports on foot; aristocrats played most of theirs on horseback.  Thus, games played on foot were called “football”, whether they had anything to do with kicking a ball or not.  Indeed, many of the earliest forms of football involved carrying balls in an attempt to get across goal lines passed some opposing team or individual players.
  • The first broadcast of the yellow line (called the “1st and 10 system”) was produced by Sportvision and occurred on September 27th, 1998 during a Bengals-Ravens game. A rival company, Princeton video, released its “Yellow Down Line” a few months later during a Steelers-Lions game.
  • According a recent Adweek/Harris pole, almost two thirds of U.S. adults say they currently watch NFL football (64%), including almost three quarters of men (73%) and over half of women (55%).
  • The 2011 Superbowl was the most watched television broadcast in history with an estimated 111 million people tuning in. The 2010 Superbowl was the second most at approximately 106.5 million viewers. The series finale of M-A-S-H is No. 3. at just under 106 million.  It should be noted that during the M-A-S-H broadcast, the number of households with access to a TV was significantly less than today, making M-A-S-H’s achievement all the more impressive, particularly considering M-A-S-H is the only non-Superbowl broadcast in the top 5 most watched broadcasts.
  • NFL games have more than twice the viewers (averaging 20 million) than networks have watching their prime-time programming.
  • The first rules for American football were written at the Massasoit Convention in 1876.
  • The Latrobe Athletic Associations Football Team was the first to play a full season with only professionals in 1897.
  • In 2011, the top 10 television markets for the NFL were: 1. New York 2. Los Angeles 3. Chicago 4. Philadelphia 5. Dallas-Ft. Worth 6. San Francisco-Oakland 7. Boston 8. Atlanta 9. Washington DC 10. Houston
    • August 15, 1994 Azteca Stadium American Bowl (Mexico City) Cowboys vs. Oilers 112,376
    • August 17, 1998 Azteca Stadium American Bowl (Mexico City) Cowboys vs. Patriots 106,424
    • August 22, 1947 Soldier Field College All-Star Bears vs. All-Stars 105,840
    • September 20, 2009 Cowboys Stadium Regular Season Cowboys vs. Giants 105,121
    • August 4, 1997 Estadio Guillermo Canedo American Bowl (Mexico City) Broncos vs. Dolphins 104,629
    • January 20, 1980 Rose Bowl Super Bowl XIV Steelers vs. Rams 103,985
    • January 30, 1983 Rose Bowl Super Bowl XVII Redskins vs. Dolphins 103,667
    • October 2, 2005 Azteca Stadium Regular Season 49ers at Cardinals 103,467
    • January 9, 1977 Rose Bowl Super Bowl XI Raiders vs. Vikings 103,438
    • November 10, 1957 L.A. Coliseum Regular Season 49ers at Rams 102,368
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  • it’s “voila,” not “walla”…otherwise a great article that answers many of my drunken Sunday ponderings

  • Nice entry, thanks

  • By “Walla!”, I think you meant “Voilà!”:

  • Maybe the author was using this form or WALLA: In American radio, film, television, and video games, walla is a sound effect imitating the murmur of a crowd in the background. A group of actors brought together in the post-production stage of film production to create this murmur is known as a walla group. According to one story, walla received its name during the early days of radio, when it was discovered that having several people repeat the sound walla in the background was sufficient to mimic the indistinct chatter of a crowd. Nowadays, walla actors make use of real words and conversations, often improvised, tailored to the languages, speech patterns, and accents that might be expected of the crowd to be mimicked.

  • Walla? And I am supposed to believe these posts are 100% correct? Why do they need to know where every camera is on the field when they only show the 1st down marker/line from the side at the snap?

  • Yes but where id the line actually please?