Individual Channels for Color Matching

Individual Channels for Color Matching

Many After Effects artists completely ignore that pop-up
menu at the top of the Levels control that isolates red,
green, blue, and alpha adjustments, and even those who
do use it once in a while may do so with trepidation; how
can you predictably understand what will happen when you
adjust the fi ve basic Levels controls on an individual channel?
The gradient again serves as an effective learning tool
to reveal what exactly is going on.
Reset the Levels effect applied to the Ramp gradient once
more. Pick Red, Green, or Blue in the Channel pop-up
menu under Levels and adjust the Input and Output
carets. Color is introduced into what was a purely grayscale
image. With the Red channel selected, by moving
Red Output Black inward, you tint the darker areas of the
image red. If you adjust Input White inward, the midtones
and highlights turn pink (light red). If, instead, you adjust
Input Black or Output White inward, the tinting goes in
the opposite direction—toward cyan—in the corresponding
shadows and highlights. As you probably know, on the
digital wheel of color, cyan is the opposite of red, just as
magenta is the opposite of green and yellow is the opposite
of blue (a sample digital color wheel and a visual guide to
how levels adjustments operate on individual channels are
included on the book’s disc).
Gradients are one thing, but the best way to make sense
of this with a real image is to develop the habit of studying
footage on individual color channels as you work. This is
the key to effective color matching, detailed ahead.
Along the bottom of the Composition panel, all of the
icons are monochrome by default save one: the Show
Channel menu. It contains fi ve selections: the three color
channels as well as two alpha modes. Each one has a shortcut
that, unfortunately, is not shown in the menu: Alt+1
through Alt+4 (Option+1 through Option+4) reveal each
color channel in order. These shortcuts are toggles, so reselecting
the active channel toggles RGB. A colored outline
around the edge of the composition palette reminds you
which channel is displayed.

Try adjusting a single channel of the gradient in Levels
while displaying only that channel. You are back on familiar
territory, adjusting brightness and contrast of a grayscale
image. This is the way to work with individual channel
adjustments, especially when you’re just beginning or if
you are at all color-blind. As you work with actual images
instead of gradients, the histogram can show you what is
happening in your image.