Apple Color 1.0 - Manual (Page 171)

Chapter 9 Primary In 171
Adjusting the Midtones
The Midtone contrast slider lets you make a nonlinear adjustment to the distribution of
midtones in the image (sometimes referred to generically as a gamma adjustment).
What this means is that you can adjust the middle tones of the image without
changing the darkness of the shadows or the lightness of the highlights.
Here are two examples of using the Midtone contrast slider. The midtones have been
lowered in the following image. Notice how the overall image has darkened, with more
of the picture appearing in the shadows; however, the highlights are still bright, and
the shadow detail has not been lost. The top and bottom of the gradient’s slope in the
Waveform Monitor remain more or less in place, and the slope itself curves downward,
illustrating the nonlinear nature of the adjustment.