User guide

KeylightThe Foundry

ADVANCED KEYING

Screen Balance

Foreground Pixel If the primary component in the pixel is not the same as the primary

component of the screen colour we have a foreground pixel, and the alpha is

set to completely opaque. The pixel colour is not modified. See

Figure 20.

Figure 20. Foreground pixel gives full alpha.

Screen Balance

Saturation is measured by comparing the intensity of the primary

component against a weighted average of the two other components. This

is where the Screen Balance control comes in. A balance of 100% means

that the saturation will be measured against the smallest of the other two

components in the screen colour.

A balance of 0% means that the saturation will be measured against the

larger of the other two components. A balance of 50% will measure the

saturation from the average of the other two components.

The appropriate balance point for each image sequence you key will be

different depending on the colours in that image. Generally speaking, blue

screens tend to work best with a balance of around 95% and green screens

with a balance of around 50%. If the key is not working too well with these

settings, try setting the balance to about 5%, 50% and 95% and see what

works best.