How do they make those fake yellow first down lines appear on the field during televised American Football?

They appear to be painted on the field – even as the players walk on top of them. Is it just graphics magic?
I get that they aren’t really there.. *pause for a dramatic eye roll*… I was hoping someone could explain the magic…

The Technology
One of the funniest things about computer-generated video effects is the amount of effort it takes to do seemingly simple things. The most basic concepts can sometimes take a gigantic amount of effort to implement (see How Centropolis FX Creates Visual Effects and How Industrial Light & Magic Works for interesting background).

Painting a virtual first-down line on a Football Field is an excellent example of this process. The idea to paint a first-down line across the field on people’s TV screens sounds so simple. As it turns out, implementing this is incredibly complex. It takes a tractor-trailer rig of equipment, including eight computers and at least four people, to accomplish this task!

The lines are computer generated for TV audience and cannot be seen on the ground at the field by anyone.

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