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eZedia Resources
eZedia Tips & Tricks
 From Hawaii, With Love: How to Shoot Blue Screen Video for iMovie
Blue Screen, also known as Chroma Key, is a technique used in video special effects to place an actor or object in front of a different background. It was used heavily in movies like The Matrix and Star Wars: Episodes I/II/III to place actors in digitally created environments. eZeScreen™ provides Mac OS X users with a simple solution for creating blue screen composites with iMovie.
So how does it work?
To start your blue screen project, you'll need to shoot video of your actor in front of a large, solid-colored backdrop or screen. While the color of the backdrop is usually blue or green, depending on the circumstances, it doesn't have to be. eZeScreen can remove the blue (or any other color) areas of the screen and layer the actor over any background video you choose.
Make sure your actor is wearing clothes with colors that are not too similar to the color of your screen, or they will become transparent with the screen when you apply the blue screen effect! This is usually the primary factor in the decision between choosing a blue or a green screen.
Lights...
The best thing you can do while shooting for blue screen is to make sure your backdrop has even lighting. To the camera, the backdrop should appear solid - no shadows, gradients, creases, or reflections should show up in the final take. Make sure that the lighting for the screen is behind the actor.
If you don't have a good broad light to evenly light the backdrop, try reflecting light onto the background by shining a spotlight onto something like white Foamcore. Be careful not to over-light the backdrop, because the color of the backdrop will reflect onto the actor, a condition known as background reflection or spill.
Light the actor separately from the backdrop. Move your actor as far away from the backdrop as possible, to avoid having foreground lights or shadows from the actor show up on the backdrop. Keeping your actor farther from the background also helps reduce spill.
If you have the resources, soft-lighting your actor from the sides or rear will help separate him or her from the background, and further reduce or eliminate the chance of spill. If you want the most realism, study your background footage and try to duplicate its lighting in your studio.
Camera...
Watch your background footage closely to make sure the camera angle didn't change during the film shoot. If it does, you will have to try to duplicate that movement with your own camera - which will be near impossible!
Make sure your actor is being filmed in a way that would suit the background. Some shots will work better with a close-up, others are more suited to a wider body shot. To simplify things, make sure the actor's feet are not visible. Full body shots are very difficult to composite realistically. It's also important to have the backdrop fill the frame, otherwise the edges will show up in your final composite.
If you have a camera that allows manual shutter speeds, try increasing the shutter speed past the default. With a higher shutter speed setting, you should get crisper edges, allowing for better background masking. Experiment with this to get the best setting for your scene.
Action!
Make sure your tripod is sturdy, and record away. The hard part is out of the way... whew! Now on to the fun stuff in iMovie!
Import your movie and background footage into your iMovie project using the standard method. All you need to do is apply your actor to your background clip as an eZeScreen effect. For more information on using iMovie, refer to iMovie's online Help.
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