Digital imaging: first down line in football

[Naty1]

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??

 

[russ_watters]

The field is green - the technology is the same as a greenscreen.

 

[Wetmelon]

I've always wondered, what about the Packers? They're green too. How come they don't become the first down line?

 

[Naty1]

Russ...what is greenscan??...never heard of it...no hit in wikipedia...
Thanks

 

[dlgoff]

It's greenscreen not greenscan.

http://en.wikipedia.org/wiki/Chroma_key"

 

[Naty1]

Don thanks...
odd that the Wikipedia search engine can't suggest 'greenscreen' for 'greenscan'...a 'greenscreen' search entry immediately turns up your refrenced page...

 

[turbo]

Does your local weatherman have active radar displays, updated temperatures and wind speeds, etc on maps behind him? Same technology.

 

[sophiecentaur]

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?

 

[Mech_Engineer]

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...

 

[Mech_Engineer]

Ask, and you shall receive:

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

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.