Secondary Color Correction Primer - The Art and Technique of Digital Color Correction - page 166

Qualifications in secondaries are done in three basic ways:

T I P
Increased contrast is one of
the brain's visual cues that
something is closer to us
(and therefore inherently
more important).

1. Isolating a specific color vector or luminance range or a combina-
tion of the two

2. Using a shape to define a portion of the image

3. Using a combination of the two

For all three of these methods, the basic concept is to create a matte or
mask that limits the correction to a specific portion of the image.
There are also three basic steps to doing a secondary color correction:

1. Determine what you are trying to accomplish

2. Figure out how you can qualify the correct portion of the image
without qualifying unwanted areas

3. Make a correction inside and/or outside of that qualified area

Let's take a look at the three methods of color correction and walk
through each of the three steps with each method.

Color Vector Isolation

One of the main secondary color correction qualification methods is to
isolate a specific color vector and alter it in some way. This is a very good
way to do secondaries as opposed to “vignettes” or “spot” color correc-
tion, because you don't have to worry about camera movement or things
crossing the foreground. The color corrections that you apply to a specific
color vector isolation or qualification stay with those pixels as long as
those pixels stay relatively the same color. They don't need to be tracked
or rotoscoped. Passing shadows or other active lighting effects or semi-
transparent foreground effects like smoke or fog will have an effect on
color vector isolations, though, as they will change the color of the image
behind it.
Each color correction application has a slightly different set of controls
to accomplish isolating specific color vectors, but most of them work very
similarly to Color. You can try to isolate the vector in the old-school way
by guessing at the correct hue and saturation and luminance values and
moving the HSL sliders until you have a clean matte, but nearly everyone
will start his or her qualification of the selected color by sampling it with
the eyedropper first.
Nearly all color correction applications have the ability to sample a
portion of an image with an eyedropper. Symphony uses a “syringe”
for sampling large areas. Each application has slight differences in how
the eyedropper works. Some—like Color—allow you to add and subtract
from your qualifications using the eyedropper and certain modifier keys.