The Secret of the Green Wall


Chief Meteorologist Bill Walsh tracks severe weather on the green wall.

The same “green screen” technology that movies use to insert special effects has been a mainstay of television news for decades. It’s called a “chroma key” effect. The chroma refers to color, in our wall’s case, a bright green, and the key refers to electronically replacing everything green with the weather maps and graphics.

So how do our meteorologists know what they’re pointing at when there’s nothing really there?


Meteorologist Chad Waston tracking storms off the coast during Live 5 News at Noon.

Simple: there are monitors on either side of the wall, so they can look to the left or right, towards the radar image, and see where they are pointing. There’s also a monitor right on the camera below the lens, so that they can look straight ahead at the viewer and still see themselves and where they’re pointing.

But even with a monitor showing you where you’re pointing, it’s still harder than it looks. Think of looking at a map: if the top of the page is pointing north, then you’d point to the west by pointing to the left side of the page. But when you’re standing in front of the map facing the camera, you’d point to your right so you’d appear to be pointing to the west on camera!

The next question we get is, “Why green?” Green and blue tend to be furthest from flesh tones, so they’re the two colors used most often. Green is a better choice than blue because if the wall were blue, it would eliminate close shades of blue from wardrobe choices. Green is a little less common in ties and suits than blue, so green makes more sense as the color to eliminate.

If one of our meteorologists wore green, especially a light, vibrant green the same color as the wall, what he was wearing would “key out,” and you’d see the map instead of the clothes. It’s not x-ray vision, but it would make him look like “the invisible man.”

So now you know how one of the oldest, continually-used TV news special effects works! And keep checking the LIVE 5 INSIDER blog for more behind the scenes secrets!


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