A quick do-it-yourself guide

Blue and green screening are techniques commonly used in special effects production to place actors and objects in front of backgrounds that can be shot or created separately. One common example is the news weather-person standing in front of a screen that changes to show the temperature, weather conditions, etc.

How it works:- To be able to place your subject against any background, you'll first need to shoot them against a painted wall or material that has a solid color on it that you can remove later in post-production using a process called matting or keying. Blue and green are used for this, because these colors are less represented in skin tone than colors such as red and yellow.

As a DAS student you will have access on a need basis to the Green Screen Studio at the REVE.

Plan Your Shoot:- Before you start have a clear idea as to how you are going to use your shot. You should know ahead of time what type of background you'll be eventually placing behind your subject. Your subject should be in scale with your background Shoot your background first or if you are using a still image have it available so you can light your subject accordingly.

Subject - Your subject should not contain the color that is used for the background. For instance, if using a green screen, don't have your subject wear a bright green shirt that matches the color of the background, unless you want their torso to appear transparent.

Lighting - Good lighting is essential to a "clean" greenscreening process. The background should be lit evenly, so that there are no dark or light patches, shiny spots or shadows. Your subject should be lit so that they do not throw a shadow on the background, if possible, and so that there is no green light bouncing off the background and spilling onto the subject. Doing all this will take some trial and error, so give yourself time.

Camera - Needless to say, you want to shoot this. You can use a still camera or any other kind of camera, depending on your situation and if you want to use moving images or not. For this process, anything that will allow you to get your picture of footage into a computer will do. Digital video cameras work great, because they can connect directly to most video equipped computers.

Computer hardware/software - Many different software programs will allow you to key out colors like blue or green. Premiere (PC/Mac) and FinalCutPro (Mac) are two of the more popular ones. AfterEffects (PC/Mac) has more sophisticated keying tools, as does Ultimatte (PC/Mac).
Probably the most interesting tool to key your Gree or Blue screen work is Z-Matte which is available as a plugin for After Effects (and other programs) and which you can find installed in at least 2 computers at the FAC Lab.

How to do it:

1) Positioning your subject – Position your subjects as far away from the background as practical (to avoid the green color spilling on your subject), or suspend objects from fishing wire. Be creative. Subjects can walk through the frame, and even disappear behind objects covered with green material.

2) Framing your shot – Make sure the angle of your camera matches as close as possible the angle of the camera that took the original footage

3) Lighting your scene - Pay special attention to shadows and bright spots on the background and reflected light on the subject. If possible light the background with a filtered light (green or blue) and your subject with a “warmer” light.

4) Import your footage - Premiere and FinalCutPro have their own import capabilties. See the individual program you're using for info.

5) Position your background footage and bluescreened subject on different layers - You'll need to put your bluescreened subject on a video layer above the background subject, to set up the transparency. You won't be able to see the background until you apply the key effect.

6) Apply the key effect - This process is different from program to program. In Premiere, it's called Transparency. In AfterEffects and FinalCutPro, it's called Chroma Key. Other options are Bluescreen or Greenscreen. See the individual program for more info. We use a plugin for After Effects called Zmatte which does an excellent job even with poorly lit backgrounds. This is available at the NAVE and at the FAC Lab.

7) Adjust the effect - Most of the time, you'll have to adjust the parameters of the effect in order to get the "cleanest" possible results. Premiere uses "Transparency" and "Cut-off". AfterEffects uses "Tolerance" and "Edge Thin". Zmatte has many more controls for multiple combined mattes and it is harder to use but gives a better result. Experiment with different types of keying effects and different parameters. You may need to apply more than one keying effect if your background had shadows or bright spots. You may need to mask out parts of the foreground, like the wire holding up your subject or the edge of the bluescreen material that got into the shot. AfterEffects is the best program for this kind of advanced work.

8) Keep practicing!