Luma Mattes

Luma Mattes

The honest truth is that I don’t use the above effects very
often; there are less immediately obvious but more powerful
ways to generate transparency from color data:
. Blending modes
. Blending modes with color adjustments
. Shift channels and levels
In the interest of full disclosure, I often use track mattes
(as detailed in Chapter 3) with a duplicate of the layer,

instead of luminance keys applied directly to the layer.
With a track matte, I can use Levels to work with color
ranges on all channels in order to refi ne transparency.
Other artists may consider this approach more cumbersome,
preferring to work with a single layer and an effect,
so the choice as always is yours.

Blue and Green Screen Keys

Keylight is useful in many keying situations, not just studiocreated
blue- or green-screen shots. For example, you can
use Keylight for removal of a murky blue sky (Figure 6.8).
You wouldn’t use Keylight to pull a luminance key, however,
or when you’re simply trying to isolate a certain color range
within the shot; its effectiveness decreases the further you
get from the three primary colors.
Keylight is most typically used on footage shot against a
uniform, saturated, primary color background, where preservation
of edge detail is of utmost importance.