Why Is Football Messing with My Reality
September 28, 2008 7:32 PM   Subscribe

There must be a simple explanation for this, but I'm damned if I can figure it out: in televised football games, how do they get the digital line of scrimmage and digital arrows marking which down it is to appear as if they're underneath the players' feet and bodies?

No one I've asked seems to know, and my limited football vocabulary is seriously impeding my search for an answer. Help?
posted by Powerful Religious Baby to Sports, Hobbies, & Recreation (9 answers total) 4 users marked this as a favorite
It's the computers, Powerful Religious Baby.


Wait, that's another thing.

But yeah, they have an image processing program do it.
posted by SlyBevel at 7:39 PM on September 28, 2008 [1 favorite]

Best answer: 'Virtual first down line' is the phrase you're missing. Here's more.
posted by holgate at 7:42 PM on September 28, 2008

Best answer: Like this.
posted by googly at 7:42 PM on September 28, 2008

The field is green, the players are not.

The first down line has terrible issues when the field is not white, like when there's snow on the field. Sometimes it looks like it's under the snow, which is a neat trick in itself.

Given that, I'm not sure how it works when the Packers play.
posted by smackfu at 7:45 PM on September 28, 2008

OK, according to googly's article: "Team uniform colors, such as the Green Bay Packers, can also be tough, as the computer has to be told not to paste the yellow line over the shades of green in players’ clothing." ...which I don't really buy. Are the shades of green in a uniform materially different than the shades of green in grass?
posted by smackfu at 7:52 PM on September 28, 2008

smackfu: speaking as someone who's highschool had a terrible, awful chroma green screen: yes, yes it does. There'd be 'bumps' in the image along patches that were put onto the screen; even though it was painted entirely 'chroma green', it hiccuped at variation.

At the same time, it would wipe anything green-tinged from the announcer's clothing, so truly, it is a wondrous system which screws everything up.
posted by flibbertigibbet at 8:14 PM on September 28, 2008

Right, in that case you have a perfect shade background, so the chroma-keying can be very exact... and is thrown off by any variation. But a field isn't a perfect green to start with, and there are lighting conditions and such, so any system has to allow for variations in the green tones, and I don't see how those are different than the variations in the uniform color. Maybe if you're lucky there's no overlap, but that's not a given.
posted by smackfu at 8:28 PM on September 28, 2008

Response by poster: Nice! My understanding of this issue has been upgraded from "less than a dog knows" to "superficial," thanks to those informative links. But don't try to talk COMPUTERS to me, SlyBevel. I am like this guy.
posted by Powerful Religious Baby at 9:21 PM on September 28, 2008 [1 favorite]

With a fixed camera in a known location, wouldn't it be possible to use a known-image of the field sans players rather than chroma-key? Maybe that requires more hefty processing.

Only if you expect the blades of grass not to move during the course of the game. And have you ever watched a football game? There's not a "fixed camera in a known location" anywhere to be found.

Are the shades of green in a uniform materially different than the shades of green in grass?

posted by toomuchpete at 7:33 AM on September 29, 2008

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