Primary Color Correction: Color Control Primer - The Art and Technique of Digital Color Correction - page 106

Even after these two corrections, the midtones still look very red.
We'll sample the middle gray tone and adjust the gammas to eliminate
the cast. I scrubbed around and settled on a gray sample of 136 for red,
118 for green, and 102 for blue. As there's no absolute value given on the
chart for gray, I'm going to match red and blue gamma to green gamma.
It would also be possible to attempt this correction using the hue off-
set wheels. This method requires some real knowledge of how the colors
combine to make each other. Moving the wheels to match the numbers
of the sample is a little like trying to solve the Rubik's cube puzzle. Some-
times as you get close to “solving” one color, one of the other colors drifts
away, and it doesn't seem like you can move the hue offset wheels in
a direction that solves all three colors. For example, when trying to get
highlights of red and green down and blue up, I pulled down toward blue
until the number for blue got close to 235, and then I had to maintain the
distance from the center while I swung the hue offset wheels clockwise
and counterclockwise to get the red and green numbers to match. This is
actually a good exercise to learn the hue offset wheels. You can also adjust
the hue numerically with the arrow keys.
Using very subtle movements in the wheels, try to match numeri-
cal values of each channel. Of course, you want to make sure that your
sample is of a black, white, or gray image and that when you are control-
ling the midtones, the sample is of a midtone area. You shouldn't sample
a black chip and try to balance it using the midtone wheel, of course.
Another good exercise is to load up a chip chart like the “ChromaDu-
Monde_warm” clip from the exercise in this section and use the hue off-
set wheels to balance while looking at an RGB parade. This exercise is
considerably simpler with a manual interface like the WAVE or Element
by Tangent Devices ( Figure 3.41 ) , Avid MC Color, or JLCooper Eclipse
that allows you to control all three hue offset wheels at once.
Fig. 3.41 Tangent Devices' Element color control panel.