Football visuals question.

[CoolBreeze]

I've never watched a complete game of football in my life. I don't care about it or any other sport for that matter. I have always said that I don't care to watch sports or porn for the same reason: Why would I want to watch somebody ELSE have all the fun? If I want to have fun, I'm the one going to right in the middle of it, which is why I was a skydiver for 35 years.

Now to my point:

I was skipping through the channels and see a Cincinnati vs Cleveland game in progress. Right before each play, I see a blue line running across the field which then disappears. Sometimes an orange line appears also. How do they do that? You can see the players walk right on that line, and the line never covers the numbers on the field either. I'm assuming that they are using the field itself as a Green Screen. As long as the players don't wear green, should work OK. Am I right?

[genlock]

They use different color LED's embedded in the grass.
The linesmen control them with the first down markers and the line of scrimmage flag.
They are powerful and can be seen thru snow or mud.

I would go back to skydiving if I were you.

[genlock]

It is really some kind of computer trick.
I have never worked with it so I don't know how it works.
I remain amazed by zoom lenses.

[genlock]

It is really some kind of computer trick.
I have never worked with it so I don't know how it works.
I remain amazed by zoom lenses.

[The-Hammer]

Whenever ESPN comes to town they hire a bunch of students from the journalism program to help out. About 6 years ago I worked with the guy who did the "First and 10" line. I'm not an expert, but this is my understanding of the system.

There are two components: a set of boxes on the cameras and a computer.

The boxes read the exact pan, tilt and zoom settings from each camera. That way they can keep the line in the right place even when the camera moves. The tripods are tightly anchored to the surface so that they can't move and lose alignment.

The computer component is, as you suggested, just a green-screen system. Each camera has two feeds, the plain (top left) and the chroma-keyed (top right). The computer takes the chroma-keyed feed, filters just the line they want (bottom left), then overlays it on the plain feed (bottom right).

First and Ten Line.gif

EDIT: As you say, it _is_ a problem when the players are also in green.

[CoolBreeze]

I'll have to say this, however it's done: Even a person like me who has little understanding of the game can appreciate those lines... and actually seeing where the players have to go.

[genlock]

Now, If only the football didn't disappear on passes and kicks, we could all enjoy it.

[Bar Rat]

ESPN's on-field down and distance graphic has some red in it. During the Eastern Washington-Villanova game (which I watched because I wanted to burn my retinas with the red field), I could occasionally see it on the helmets of EWU's players because the shade of red was so close to the one used in the graphic.

[Lester]

http://www.howstuffworks.com/first-down-line.htm

[Bar Rat]

http://www.howstuffworks.com/first-down-line.htm

Thanks That's an excellent article!

[CoolBreeze]

The thing that amazes me most is that according to the article referenced above, this system has been used in some form or another since the late 90s. I scan past a lot of football games and have never seen it till today.

Second, it's not a simple Chroma Key setup. We're talking Star Wars stuff here:


* 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.

[Lester]

Well then, you'll love this:

http://moconews.net/article/419-word-le ... iting-for/

Here's a pic I shot at Target yesterday, using the demo mode (reverse word). Pretty impressive.

[CoolBreeze]

I would LOVE to have that in my travels! (but I'd have to get an iphone or some other variation which I flatly refuse to do until monthly rates reach my land-line rates... which may be never)

It seems however... this technology would be fairly simple compared to the football stuff. I mean, we've had OCR on our personal computers since the beginning of time, and computer translation is also old news. Toss them together and have that app. (yea I know, it's not THAT simple but it's close)