User guide

KeylightThe Foundry

ADVANCED KEYING

Clip Rollback

Pulling a Screen Matte (Figure 44) will typically produce lots of transparency

(grey) in the matte at the edges. This is good since this is what you need to

key hair well. You may also get transparency in the foreground as shown in

Figure 45. This is bad as your subject will appear slightly see-through, and

this should be corrected. You can do this with an inside matte, or you can

use the Clip Max parameter to turn these grey pixels white. This cleans up

the foreground (

Figure 46) but it will also destroy the edge detail you want

to keep.

This is where Clip Rollback comes in. This is used to put back the edges to

restore the detail that was lost. A rather exaggerated clip rollback is shown

in Figure 47 to illustrate the point.

Figure 44. Screen matte highlighting the close

up view as shown in Figure 45.

Figure 45. Close up screen matte showing

unwanted (grey) transparency in the (white)

foreground.

Figure 46. Clip White has been used to

remove the unwanted grey pixels in the

white matte.

Figure 47. Clip Rollback has been

used to reduce the unwanted erosion

of the edge.