Primary Color Correction: Tonal Correction Tools - The Art and Technique of Digital Color Correction - page 36

Another very common way in computer applications to adjust
tonal ranges is via curves. Curves is a popular tonal correction tool
because it offers incredibly precise control and is very intuitive. So
you'd figure that it is the tool to use for tonal corrections, but there
is a caveat: you can really screw up your images with this tool. Most
applications that have curves allow you to place as many as 16 distinct
points on the curve to control it. All of these points can do some very
funky things to your image, including creating severe posterization
or banding. Patrick Palmer, formerly of IRIDAS and now with Adobe,
points to these issues as the reason Speedgrade does not have Curves.
Curves is a favorite tool of Photoshop users, After Effects users, and
those who move back and forth between Photoshop and video applica-
tions. Full-time colorists are much less enamored of this tool, though
with exposure to it through Apple's Color and DaVinci Resolve, that
may change.

D e f i n i t i o n
posterization: Posteriza-
tion happens when an
image breaks down from
having continuous tones to
having specific regions of
tones where each region
has a distinct transition to
the next ( Figure 2.2 b ). This
effect is similar to banding. Fig. 2.1 Tangent Devices Elements control panel.

(a)

(b)

Fig. 2.2 (a) Original image (16 mm film transfer to HD courtesy Vanderpool Films). (b) Posterized image.