Green-Screen Tips, Tricks and Techniques

Green Screen: A technique for mixing two images together, in which a color from one image is removed, revealing another image behind it.


1. Begin with the end: Before you even shot a frame, think ahead about what the background of your project will look like. If your project entails showing talent in an ultramodern apartment hosting an evening cocktail party, not only should you light for ambient interior, but you would also be able to choose the appropriate camera height and lens that would ensure your footage composites well. The more planning and vision you have at the start, the more cohesive your work will be when it’s all done.

2. Stay away from the background: Keep your talent at least 10 feet away from the background. This will lessen your spill and if you’re using a longer lens. It will also help separate the subject from the chroma key, which will give you cleaner lines all around.

3. Use a kicker: Even a slight backlight will really help separate your talent from the stage. Keep it hotter around the torso and head, and watch the spill from the backlight. That overflow of light onto the foreground can cause more headaches in post than the time it would have taken to adjust in production.

4. Un-sharpen that camera: Most HD cameras have an “un-sharpen/sharpen” mode. To sharpen your footage is asking for the camera to compress the input, which produces a slightly jagged, or bit mapped edge. Setting your camera to un-sharpen provides a cleaner shot and will improve the keying process.

5. Shoot a plate: Before any talent walks onto the set, roll camera for a few seconds. This footage can be used to render even sharper keys in post, since you wouldn’t be fighting against the talent’s shadows and blurs that may happen during the actual shot. The plate is a great reference for your keying application to properly separate the subjects.

6. Light it twice: Make sure your chroma key background is lit evenly. And, yes that includes the floor if you have a full shot. Plan ahead for this, as it can take several hours to get a stage lit properly. Equally important is lighting your talent according to the background or environment your project requires. If you don’t plan ahead for the look you want to end up with, this could throw uneven chroma levels onto your background, which will affect your keyed footage.

7. Use a Vectorscope: The bottom line is that light meters don’t work well enough for a green screen shoot. You need to see how the chroma and luma levels are looking, and where the hot spots are. The only way to see them is with a Vectorscope.


Source: http://brajeshwar.com/2008/green-screen-video/