Download Nuke 6.2v2 User Guide

KEYING WITH ULTIMATTE
Using Overlay Tools and Screen Correct
• spill suppression - check this to use the controls on the Spill tab.
• cleanup - check this to use the controls on the Cleanup tab.
• color conformance - check this to use the controls on the Color tab.
Using Overlay
Tools and Screen
Correct
Screen Correct compensates for anomalies in the backing area such as
uneven lighting, smudges, seams, variation in the backing color, green set
pieces, and unwanted shadows cast by set pieces, boom arms, etc. This
technique assumes that an exact copy of the problematic green screen
element with the subject matter omitted, usually called a Clean Plate, is
supplied.
Although this technique gives great results by differentiating between
foreground elements and backing flaws, you often haven’t got the necessary
reference materials. In that case, you can create a synthetic Clean Plate
with Ultimatte.
To achieve the best results, use a reference Clean Plate as an input to
Ultimatte in addition to allowing Ultimatte to generate a synthetic plate. In
this way, the reference plate allows for the best shadow separation, while
the synthetic plate is be used to reduce such artifacts as film grain or video
noise (which is rarely accurately reproduced when the clean plate is shot
during the time of principal photography). Switch the view to screen by
clicking the overlay dropdown and selecting screen.
With screen correct selected, use the add overlay tool to scrub on areas
that represent the green screen, including shadows. Usually, it’s best to
press Alt+Ctrl/Cmd while scrubbing, so that you are picking the color in the
input image at that pixel, instead of the color of the processed image.
The overlay will be used in the final process to fully eliminate these areas
from the final composite. Continue in this manner until the foreground
subject and its shadows are surrounded with an overlay. Make sure the
overlay does not cover any foreground detail that is to be retained. If the
overlay does cover foreground subject matter, then use the remove overlay
tool to scrub on those areas that should not be covered by the overlay.
Repeat these two processes until the overlay covers the green screen areas
and no subject matter. View the composite in the Viewer to see the screen
corrected composite with anomalies in the backing area removed. To learn
which controls were automatically set by Ultimatte, click the Screen Correct
tab and note the position of the controls.
The Foundry
Nuke 6.2v2
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