Apple Color 1.5 - Manual (Page 268)

Note: You can manually set the key blur to even higher values by typing them directly
into the Key Blur field.
No key blur With key blur
One of the nice things about keying for color correction is that, unlike keying to create a
visual effects composite, you don’t always have to create keyed mattes with perfect edges
or completely solid interiors. Often an otherwise mediocre key will work perfectly well,
especially when the adjustment is subtle, so long as the effect doesn’t call attention to
itself by adding noise, or by causing vibrating “chatter” around the edges of the matte.
For example, holes in a keyed matte often correspond to shadows that are falling on the
subject you’re isolating. If you’re making a naturalistic adjustment to the highlights of
the image, you probably don’t want to include such shadowed areas in the correction,
so there’s no need to make further adjustments to the matte.
Check Your Secondary Keys During Playback
It’s always important to double-check to see how the secondary keys you pull look
during playback. Sometimes a secondary operation that looked perfectly good while
you were making the correction exhibits flickering or “chatter” at the edges that is the
result of noise, or of including a range of marginal values that are just at the edge of
the selected range. (This happens frequently for “hard-to-key” features in an image.) In
these cases, additional adjustments may be necessary to eliminate the problem.
Also, secondary keys that work well in one part of a shot may not work as well a couple
of seconds later if the lighting changes. Before moving on, it’s always a good idea to
see how a secondary operation looks over the entire duration of a shot.
Controls in the Previews Tab
The Previews tab is a two-part display that helps you guide your adjustments while you
use the HSL qualifiers and the vignette controls. Two reduced-resolution images show
you different views of the operation you’re performing.
268 Chapter 10 The Secondaries Room