The target lighting level for a blue or green screen varies slightly, but in general should be around .70 of the full range of the green channel in Previzion. The red and blue channels, of course, should be as low as possible. See “Lighting Practice and Light Meters“ for more information on how to convey this to a lighting crew.
The above image was taken of a digital green background with standard light on a 4:2:2 camera. As can be seen, the RGB values at the sampling point are:
- R: 0.46
- G: 0.70
- B: 0.25
When using a digital green screen the use of green fluorescent tubes is frequently unnecessary, and can often cause problems with the green screen reflecting on other objects or people in the scene. For most productions it is best to match the existing fixtures. If the rest of the set is lit with normal quartz tungsten bulbs 3200k tungsten tubes should work just fine on your fluorescents.
Space lights are very nice for lighting the floor of a stage because they cover a large area and provide soft light.
Fluorescent lights like Kino Flo lights light green screen walls nicely because they have a short to medium throw and are soft and able to cover a large area.
Blue Screen Lighting
Blue screen lighting is much less forgiving, and this is one of the reasons why green screens are so much more common than blue screens at present. The despill operation on a green subject resolves to a grayish fringe, which can be easily re-tinted to blend into a given background. Also 4:2:2 video has twice as much information on the green channel which will make for smoother edges. For more information on blue vs green screen see the section “Blue vs Green Screen“
The despill operation on a blue screen subject resolves to a harsh magenta edge, and this is extremely difficult to remove, and explains a lot of the ugly dark lines around older composite images. Motion blur is also a problem with blue screens with inadequately separated light; this will show up as magenta streaks whenever someone moves quickly in the scene.
The solution is generally to light blue screens with gelled lights (Lee 079 Just Blue), or color matched Kino-Flo fluorescent bulbs. When lit with this type of lighting, Digital Blue screens will provide color channel differences similar to that of the lit green screen to the left, and will not have the magenta artifacts mentioned above.