Primary Color Correction: Tonal Correction Tools - The Art and Technique of Digital Color Correction - page 65

In the image of Brian in Figure 2.34 , I used the Luma Range editing
tools so that there would be a good distribution of black, gray, and white
in the image. The actual source image shows up as mostly gray and white
when no Luma Range editing is done.
Luma Range Editing
With Color Finesse and Avid Symphony, there are ways to alter the defini-
tions of the three Luma Ranges: shadows, midtones and highlights. In other
words, you can determine what the application considers to be shadow and
where it transitions to being a midtone and then where midtones become
highlights. For most normal images, you don't need this kind of control.
The definitions make sense and give you the kind of control you want. But
for certain shots, you may want to alter the definitions of these tonal ranges
so that you can gain greater control over specific parts of the picture. I don't
have specific technical information from the manufacturers, but I would
assume that most applications consider the range from 0IRE to about 25IRE
to be shadows, from 25IRE to 75IRE to be gammas and from 75IRE to
100IRE to be highlights. Obviously, these numbers (even if they're right)
wouldn't be hard cutoff points. It would work something like this: if you
move the shadow control, the darkest 10 percent would be affected 100
percent by the control, the next 10 percent of the darkest part of the image
would be affected 90 percent by the control and so on, until the brightest
parts of the picture aren't affected by the shadow control at all.
Avid Symphony and Color Finesse both have tools to define Luma
Ranges. They are essentially the same, though Symphony gives a little
bit of added control. At the current time, there is no ability to edit Luma
Ranges in the lower-end Avid products.
Figure 2.35 shows the Luma Range control for Color Finesse. It shows
a histogram of the image with three curving lines overlaid and two
Fig. 2.35