Perfecting Brightness with Curves

Perfecting Brightness with Curves

Curves rocks. I heart Curves. The Curves control is particularly
useful for gamma correction, because
. Curves lets you fully (and visually) control how adjustments
are weighted and roll off.
. You can introduce multiple gamma adjustments to a
single image or restrict the gamma adjustment to just
one part of the image’s dynamic range.
. Some adjustments can be nailed with a single wellplaced
point in Curves, in cases where the equivalent
adjustment with Levels might require coordination of
three separate controls.
It’s also worth understanding Curves controls because they
are a common shorthand for how digital color adjustments
are depicted; the Curves interface recurs in many—most—
color correction toolsets.
Curves does, however, have drawbacks, compared with
Levels:
. It’s not immediately intuitive, it can easily yield hideous
results if you don’t know what you’re doing, and there
are plenty of artists who aren’t comfortable with it.

. Unlike Photoshop, After Effects doesn’t offer numerical
values corresponding to curve points, making it a
purely visual control that can be hard to standardize.
. Without a histogram, you may miss obvious clues about
the image (making Levels more suitable for learners).
The most daunting thing about Curves is clearly its interface,
a simple grid with a diagonal line extending from
lower left to upper right. There is a Channel selector at the
top, set by default to RGB as in Levels, and there are some
optional extra controls on the right to help you draw, save,
and retrieve custom curves. To the novice, the arbitrary
map is an unintuitive abstraction that you can easily use
to make a complete mess of your image. Once you understand
it, however, you can see it as an elegantly simple
description of how image adjustment works. You’ll fi nd the
equivalent Curves graph to the Levels corrections on the
book’s disc.More interesting are the types of adjustments that only
Curves allows you to do—or at least do easily. I came to
realize that most of the adjustments I make with Curves
fall into a few distinct types that I use over and over, and so
those are summarized here.

Some images need a gamma adjustment only to one end
of the range—for example, a boost to the darker pixels,
below the midpoint, that doesn’t alter the black point and
doesn’t brighten the white values. Such an adjustment
requires three points (Figure 5.21):
. One to hold the midpoint
. One to boost the low values
. One to fl atten the curve above the midpoint

then to modulate it with one or two added points. More
points quickly become unmanageable, as each adjustment
changes the weighting of the surrounding points.
Typically, I will add a single point, then a second one to
restrict its range, and a third as needed to bring the shape
of one section back where I want it. The images used
for the fi gures in this section are included as single stills
on the book’s disc for your own experimentation; open
05_colorCorrection.aep to fi nd them.