User guide

KeylightThe Foundry

ADVANCED KEYING

Clip Levels

Source Alpha If your blue screen material has an embedded alpha channel, setting the

Source Alpha to "Use As Inside" will add this matte to any internal inside

matte.

Figure 39 shows a Screen Matte that needs improving. The

embedded alpha in the source clip is a rotospline around the inside of the

woman.

Figure 41 shows how this source alpha used as the inside matte has

improved the screen matte.

Clip Levels

The clip levels are adjusted using two parameters - Clip Min and Clip Max.

Any alpha value at or below Clip Min will be set to zero and any alpha value

at or above Clip Max will be set to 100.

Figure 42 shows the original alpha

of an image and Figure 43 shows the result of clipping it.

Notice how the grey areas in the black background have been reduced and

that the grey edges have hardened up considerably. When compositing, the

Clip Min control can be used to improve the background image if parts of

the foreground are showing through. The Clip Max control on the other

hand can be used to firm up the centre of the matte, making it less

transparent to the background.

Note

You need to be really careful if you chose to use Clip Min and Clip Max that you

don't destroy the edges on your foreground. It is possible to use Clip Rollback to

compensate for this.

Figure 39. Screen Matte.

Figure 40.

Figure 41. Combined Matte.

Figure 42. Clip Min = 0. Figure 43. Clip Min = 50.