Chroma-Keying Made Easy, part 2 of 3

The previous post talked about how to use chroma keying (blue-screen/green-screen) techniques in home video, relatively inexpensively.  The question is, so now what can you do with that?  Really, it’s up to you and your imagination.  The most obvious use is to put yourself in front of a background which, for practical reasons, is difficult to film.  Here’s one example in which filming the scene for real would have caused a number of problems.  So instead, I filmed the background while driving, and filmed myself running in place and cycling on a stand, both in front of a screen.  You can tell it doesn’t completely work, because the scenery moves much quicker than I appear to pedal!  But what about placing yourself in an exotic location?  Or in the scene of a favorite movie?  Or even on the set of the Simpsons?  You can even create a video in which you are talking to yourself.  Or multiple versions of yourself.

Once you start playing around with ideas like these, you realize that it’s almost always necessary to resize one or more of the clips in order to make it work.  And then it gets more interesting – now you realize you can create a video in which you are being chased by (your) giant dog.  Or tower above buildings.

The example below, from a video contest entry centered around Dr. Seuss’s “Green Eggs and Ham” uses multiple chroma-keyed video clips to recreate a version of the book’s cover.  To give you some ideas, I’ll dissect it and explain how it was done.

The clip consists of a background – the solid orange with the letters and the white part at top right (created using photoshop and a graphic tablet/pen).  In addition, there are two chroma-keyed elements:  the person standing on the edge of the plate, and the child waving in the corner.  The plate with eggs was supposed to be chroma keyed, but it didn’t work.  Can you guess why?

I used a tripod to film myself in fron of a blue screen, and did the same with my daughter (top right).  Notice neither of us are wearing any clothing that approaches blue or green.  There’s still a bit of a blue edge along my back because the lights were off to the side.  Be sure and use proper lighting as described in my previous post.  For the plate, I simply stretched the blue screen on the floor, and placed the plate as you see it (yes, the eggs really are green) on the blue screen material.  I used a small tripod to photograph the plate at the right angle (you might try a few different angles so you have a few options).  But then I ran into a snag – the green in the eggs is too similar to blue, and no matter how I adjusted the chroma key properties, I either picked up nuances of the blue screen, or the green eggs had transparent spots or altered areas of green.

Luckily, however, the eggs were a still photo – and that’s what photoshop is for.  I used the magic lasso tool to cut out the plate, and simply pasted it on a background of the exact same shade of orange.  You can then either add the eggs to the background still, or run it as a separate video element, which allows you to adjust the size later on.

The first 8 seconds of this video show what everything looks like together:

In my next post, I’ll take this a step further, and we’ll combine a few additional chroma-keyed elements with additional “photoshopped” still items.  I’ll show you how to make a “virtual” blue screen, and cause the items to move on screen using keyframes.

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