User guide

KeylightThe Foundry
ADVANCED KEYING
22
Unpremultiply
• Status - displays an exaggerated view of the key so you can make a
more informed decision on how to improve the result.
See “Status” on
page 22.
• Screen Matte - displays the matte created as a result of picking the
screen colour.
• Combined Matte - displays all the screen matte, inside and outside
mattes and any Source Alpha added together. The combined matte is
used to composite the foreground over the background layer.
• Inside Matte - displays the matte that firms up the foreground.
• Outside Matte - displays the matte that cleans up the background.
Unpremultiply
Use this switch to set the premultiplication of the RGB channels in the
output image. If turned off, the RGB values will be multiplied by the alpha
channel, thus transparent areas are always black, and semi-transparent
areas are dark. If turned on, the RGB values of the output image will be not
multiplied by the alpha, thus semi-transparent pixels will have full
brightness in the RGB channels.
If colour correcting the image after the Keylight node you should switch on
Unpremultiply.
Status
The Status is one of the options in the Render menu and shows an
exaggerated view of the key so that you can make a more informed decision
when fine tuning the composite.
Figure 31 shows the Status after the
screen colour has been picked from the image shown in Figure 30.
Three colours are displayed. Black pixels represent pure background in the
final composite. White pixels are pure foreground and grey pixels are a
blend of the foreground and background pixels. The grey is just one colour
Figure 30. Green Screen. Figure 31. Status.