Primary Color Correction: Tonal Correction Tools - The Art and Technique of Digital Color Correction - page 64

look at a waveform display and figure out approximately what parts of the
image on the video monitor correspond to the waveform display.
Luma Range Display
The skill of knowing what parts of the image on a waveform will be
affected by a specific tonal correction isn't important only in using curves.
You also have to be able to do this if you're just using shadows, midtones,
and highlights. Color Finesse and Avid Symphony have a nice function
that allows you to develop this skill. It's called Luma Ranges. In Color
Finesse, this is one of the main viewing modes at the bottom of the list
of tabs in the upper right pane. When you view your source using Luma
Ranges, it shows you each of the three tonal ranges as a shade of black
and white. So parts of the image that you would control with the shadows
control are black. Parts that are considered midtones are displayed in gray,
and parts that are considered highlights are white ( Figure 2.34 ) .
Import some of the test images from the DVD, or bring in some movies
and images of your own and try to guess what the resulting Luma Range
display will look like. This is a fairly simple exercise with a well-lit image,
but if it's over or underexposed, your eye will get fooled into spreading
the tonal range. For example, on an underexposed image, you will be
surprised how little of the image is considered a highlight.
Fig. 2.34 Luma Range GUI in Synthetic Aperture's Color Finesse 2.