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Puppet Kaos - where Kelvin Kao plays with puppets and tell random stories

How to Do a Green Screen Effect

I’ve already written a tutorial on how to do a green screen effect before, but I thought the example wasn’t the best because it wasn’t the best example since I was replacing the green with something that’s also green. So here is a better example from the last video Start A Band. As usual, it’s done in Adobe Premiere Pro but any editing software with chroma key function can achieve this effect.

Step 1: Film the Footages

First, you need to film some footage in front of a green background. In the picture, you see a puppet in front of a piece of green fabric taped to the wall. The more standard green screens are usually of a lighter shade. I wanted to give this shade a try, though, since I happen to have this piece of fabric in my room. Also, the editing will remove the green and show whatever background you put in, so you’ll need a background as well. In this case, I want the puppet to be in front of a blackboard so I drew one.

green_screen_originalgreen_screen_background

Step 2: Put the Footages into the Timeline

In the timeline, make sure the green screen footage (brad math.avi) is in the layer above the background (classroom.bmp). This is so the character appears in the foreground, instead of being covered up by the background picture.

green_screen_layers

Step 3: Chroma Key

In Premiere, it’s under Video Effects => Keying => Chroma Key. First, use the dropper to pick a shade of green that’s close to majority of the background. Ideally, a green screen should be lit evenly so it only contains one shade of green. However, my lighting isn’t that good at the moment, so it will requires more tweaking during editing. In this case, I changed the similarity parameter to get a wider range of green removed. If this value is too small, then some green will not be removed. If this value is too big, something that aren’t that green (such as blue) will start to be removed as well.
green_screen_chroma_num

And you’ll get something like this:

green_screen_chroma_key

Notice that some of the edges weren’t cleaned up that well (I pointed them out with those red arrows). There are certainly a few more things you can do to clean it up some more.

For example, you can use a garbage matte, which gets rid of those things around the edge of the video by keeping only the area you defined using a quadrilateral (Look! A math term! How fitting!).

green_screen_garbage_matte

And also I want to move the character to the side, so the math problem on the blackboard is seen more clearly.

green_screen_done

So there it is, a green screen effect. The next post will be about how to use this same green screen effect to accomplish the shot in the Start A Band video in which the whole band is seen playing together.

Related Posts:
Start A Band Music Video
How to do a green screen effect – the theory
How to do a green screen effect – case study
How to do a garbage matte effect
Using a garbage matte effect to put a character in a car

Comments

  1. April 16th, 2009 | 5:39 pm

    That’s pretty cool. I’ve known about the green screen for awhile but never saw it in action like this. Maybe one day I’ll get a chance to try it out.

    Melissa Donovan’s last blog post..The Elusive Verb Phrase

  2. April 17th, 2009 | 2:46 pm

    Yep, a green screen is quite useful, but it’s also kind of time consuming to get it to look just right.

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