A chromakey demo

Today, I traveled to O-A High School to discuss and demonstrate using chromakey in a video production.


First we discussed what chromakey is. As an example, several students said that is how the weather person on TV can stand in front of the weather map.

How else could you use chromakey? How would it help you tell your video story? What could this technique add to your production? Could you create visuals that never really happened?

At that, I asked for a volunteer from the class, and B stepped up. He said he liked to water ski, so we did a fast demonstration on how to create a chromakey scene.

I had brought a collapsible green chromakey background, which we leaned against the whiteboard. I had B stand in front of the background, and then I handed him a prop. I had brought a nylon rope with a stick on one end. B was to hold the stick, while a student off camera pulled the rope tight on the other end.

I quickly set up my miniDV camera on a tripod, started the tape rolling, and instructed B to pretend to water ski. Soon, he was bouncing, leaning to and fro, and for a finale, he threw the rope to the left while he fell toward the right. He did an excellent job.

Next, I went to the Avio editor that was set up in the class. Connecting my Canon camcorder to the editor, I transferred 30 seconds of B to the editor.


Years ago, I had taken a ferry from the U.S. to British Columbia. While on the ferry, I pointed my camcorder out the aft window and taped the water that churned up behind the ferry. I used that footage next, transferring 30 seconds of that to the Avio. I had the student's attention.

The Avio editor has software that let's you create a chromakey effect. They call it "bluebox," but is still the same thing: keying by removing a part of the chroma (or color) signal. We keyed the two scenes together, removed the green behind B, and in a few minutes, we had the illusion of B waterskiing in the ocean.


Again, we discussed the effect. Did this really happen; did he really water ski today? How else could we use this? Could we create a virtual stage and set, and do a TV newscast with the virtual set chromakeyed as the background? Could you show a person flying on a magic carpet? Could you hold a set of handlebars and make it look like you were riding a motorcycle? Could you pose as a reporter in historical times, and for example, interview a slave helping to build the pyramids while showing video of the pyramids in the background?

That's a lot of information to put in one class period. But they heard the facts, they helped with a demonstration, and they discussed the results. And in the end, they understood the concept.