The Ideal Green

by Dyske Suematsu  •  October 5, 2006

Not all shades of green are ideal for a green screen. To get the best key possible, we need to know a bit about how computers interpret colors. In the video world, we break up a color into three components: hue, saturation, and brightness. You want the hue to be as different as possible from the hues in the foreground. In terms of saturation and brightness, the more saturated and brighter, the better.

Exhibit A

In Exhibit A above, the color on the left is a typical green that you get with green screen footage. I took this green and set the saturation to 100%; the result is the middle. I then took this green and set the brightness to 100%; and you have the one on the right. Given the same hue, this is the best possible green you can have for a green screen. Although, you will never get this kind of green in reality, you can see that the one on the left has a lot of room for improvement.

Below, you see three examples (Exhibit B, C, and D). “S” stands for saturation and “B” stands for brightness. The numbers are in percentage. In terms of brightness, Exhibit B is the best, followed by C and D. In terms of saturation, it goes in the opposite order. In this sense, none of them are better than the others. Thus, when you are lighting the background, try to keep in mind both saturation and brightness. The brighter is not necessarily the better. You want it to be both bright and saturated.

Exhibit B

Exhibit C

Exhibit D

Making something brighter is easy. You put more lights on the set or let more light into your camera. But, achieving a higher saturation level is not so obvious.

Another word for saturation would be color contrast. In photography, this is achieved in several ways. Naturally, the most important thing would be to use paint, cloth, or seamless that has the highest possible saturation. Cloth and paint designed specifically for green screen seem to have a higher saturation level in general than seamless paper.

Also, you want to avoid any sheen on your green screen. It would reduce saturation, making it simply brighter and whiter. For this reason, using a polarizing filter to reduce the amount of sheen and to increase color contrast is a good idea.

Having a vectorscope on the set would probably be a good idea too so that you know you are achieving the best possible green. It should also come in handy for detecting any deceptive greens on the subject, or any colors that are close to green by monitoring him/her in front of a white background.

Keyers like Ultimatte are now so sophisticated that many people feel it is not necessary to be so exacting on the set. This is not true. It is a matter of degree. The better the separation between foreground and background, the more detail information you can keep, such as hair, clean edges, foreground color accuracy, etc.. So the amount of care you put into your set contributes proportionately to the quality of your final footage.

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