Apple Color 1.0 - Manual (Page 176)

176 Chapter 9 Primary In
Most images don’t start out with the highest contrast ratio they could have. For
example, even in well-exposed shots, videocameras often don’t record black at 0
percent, instead recording black levels at around 3–4 percent. For this reason alone,
small adjustments to lower the black point often impress without the need to do much
more. In other cases, an image that is slightly over or underexposed may appear
washed out or muddy, and simple adjustments to lower the darkest pixels in the image
and raise the brightest pixels in the image to widen the contrast ratio have an effect
similar to “wiping a layer of grime off the image,” and are often the first step in simply
optimizing a shot.
In other cases, you may choose to deliberately widen the contrast ratio even further to
make extreme changes to image contrast. This may be because the image is severely
underexposed, in which case you need to adjust the Highlight and Midtone sliders in
an effort to simply make the subjects more visible. You might also expand the contrast
ratio of an otherwise well-exposed shot to an extreme, crushing the shadows and
clipping the highlights to create an extremely high-contrast look.