Digital imaging: first down line in football

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Discussion Overview

The discussion revolves around the technology behind the artificial first down line used in professional football broadcasts, specifically how it is rendered behind players and other graphics on the screen. Participants explore the technical aspects of this imaging technology, including its relation to greenscreen techniques and the challenges involved in maintaining accurate positioning and perspective during dynamic camera movements.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant inquires about the method used to place the first down line behind players and other images, noting the visual effect of players appearing over the line.
  • Another participant suggests that the technology is similar to greenscreen techniques, which raises questions about the implications for teams with green uniforms, such as the Packers.
  • A participant mentions the need for the system to accurately track the camera's orientation and movement to maintain the correct perspective of the first down line.
  • Concerns are raised about the challenges of recalculating the line's position at a high frame rate as the camera moves, as well as the need to account for the curvature of the football field.
  • Participants discuss the historical use of blue screens in imaging technology and speculate on the reasons for the shift to greenscreens.
  • Several technical challenges are outlined, including the need for the system to detect when players or referees cross the line and to manage superimposed graphics from broadcasts.

Areas of Agreement / Disagreement

Participants express curiosity and raise questions about the technology, but there is no consensus on specific technical details or the implications of using greenscreen technology in this context. Multiple viewpoints and uncertainties remain regarding the effectiveness and limitations of the system.

Contextual Notes

The discussion highlights various assumptions about the technology's operation, including the need for accurate camera tracking and the challenges posed by the physical characteristics of the football field. Specific technical details and definitions are not fully resolved.

Naty1
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I was asked how the artifical colored line now used in pro football games to mark the first down line is placed behind players and other images. And could not.

In other words, print overlays, say with team names and scores, block the underlying field images...but somehow the artifical first down line is placed behind regular screen images ...so when a player runs over the artifical first down line, for example "painted" on the field, the leg of the player remains visible as he passes over the first down line image...How do they accomplish this "3 D" sort of overlay??
 
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The field is green - the technology is the same as a greenscreen.
 
I've always wondered, what about the Packers? They're green too. How come they don't become the first down line?
 
Russ...what is greenscan??...never heard of it...no hit in wikipedia...
Thanks
 
It's greenscreen not greenscan.

http://en.wikipedia.org/wiki/Chroma_key"
 
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Don thanks...
odd that the Wikipedia search engine can't suggest 'greenscreen' for 'greenscan'...a 'greenscreen' search entry immediately turns up your refrenced page...
 
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Does your local weatherman have active radar displays, updated temperatures and wind speeds, etc on maps behind him? Same technology.
 
Weird that the initial work on picturing inlaying on TV used to use a blue screen. They suddenly appeared to change the switching colour. Why was this? Could it have been because of the need to work out of doors for large scenes?
 
Wetmelon said:
I've always wondered, what about the Packers? They're green too. How come they don't become the first down line?

For what it's worth, it's common to see a team with similar colors in their unforms that the line will show up on.

What's interesting to me is that the line stays in the correct spot even if the camera is randomly panning or zooming after a player. I've always wondered how they do that...
 
  • #10
Ask, and you shall receive:

http://entertainment.howstuffworks.com/first-down-line.htm"

HowStuffWorks said:
Here are some of the problems that must be solved in order for this system to work:

- The system has to know the orientation of the field with respect to the camera so that it can paint the first-down line with the correct perspective from that camera's point of view.

- The system has to know, in that same perspective framework, exactly where every yard line is.

- Given that the cameraperson can move the camera, the system has to be able to sense the camera's movement (tilt, pan, zoom, focus) and understand the perspective change that results from that movement.

- Given that the camera can pan while viewing the field, the system has to be able to recalculate the perspective at a rate of 30 frames per second as the camera moves.

- A football field is not flat -- it crests very gently in the middle to help rainwater run off. So the line calculated by the system has to appropriately follow the curve of the field.

- A football game is filmed by multiple cameras at different places in the stadium, so the system has to do all of this work for several cameras.

- The system has to be able to sense when players, referees or the ball crosses the first-down line so it does not paint the line right on top of them.

- The system also has to be aware of superimposed graphics that the network might overlay on the scene.
 
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