Neutralize Direction and Hotspots
When the direction or diffusion of light on a foregroundelement doesn’t match the target background environment,
that’s potentially a big problem. The solution is
generally to neutralize the mismatch by isolating and minimizing
it, rather than actually trying to fi x the discrepancy
by attempting to simulate relighting the element in 2D.
Every shot in the world has unique light characteristics, but
a couple of overall strategies apply. Once you’ve exhausted
simple solutions such as fl opping the shot (where lighting
is on the wrong side), you can
. Isolate and remove directional clues around the element,
such as cast shadows (typically by matting or
rotoscoping them out).
. Isolate and reduce contrast of highlights and shadows
in the element itself, typically with a Levels or
Curves adjustment (potentially aided by a luma matte,
described later in this chapter).
. Invert the highlights and shadows with a countergradient.
The simple way to undo evidence of too strong a key light
in a scene is to create a counter-gradient as a track matte
for an adjustment layer; a Levels or Curves effect on this
layer affects the image proportionally to this gradient. The
Ramp effect can be set and even animated to the position
of a key light hotspot.
A radial ramp is merely linear, which is not the correct
model for light falloff. Light’s intensity diminishes proportionally
to its distance from the source squared, according
to the inverse square law. An object positioned twice as far
from a single light source is illuminated by one-quarter the
amount of light. To mimic this with a gradient, precomp it,
duplicate the radial gradient layer, and set the upper of the
two layers to a Multiply blending mode.
Of course, you don’t want to fi ght the fundamental source
lighting in this way unless you absolutely have to do so;
hopefully you will rarely have to “fi x” lighting and will most
often want to work with what you’ve got to make it even
stronger and more dramatic.
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