Primary Color Correction: Tonal Range Primer - The Art and Technique of Digital Color Correction - page 2

cannot pass 110IRE. (There
are other ways to measure
the signal other than IRE,
such as in millivolts.) Also,
as our delivery systems
become more and more
digitally based, “gamut”
is also included in “legal”
levels. Not all waveform
monitors or vectorscopes
can monitor gamut levels.
These gamut levels are
the legal amounts—or
values—of certain colors.
It is possible for the lumi-
nance of an image to be
well under legal levels, but
because of a combina-
tion of saturation and
luminance, the legal gamut
levels can be exceeded.
We'll get into this more
later in the topic. In addi-
tion to “legal” levels, there
is a second, similar term
called “valid” levels.

Fig. 1.1 The graticule of a vectorscope superimposed onto a color wheel. Notice that the “targets” on the
vectorscope—the small boxes next to the black letters—correspond to the colors of the color wheel.

vector: A position or
coordinate in space or a
direction between two
coordinates. On a vector-
scope, the vector is the
specific position of a color
in the two-dimensional
circle defined by the vec-
torscope. The “targeted”
vectors on the vectorscope
are the three primary
colors—red, green, and
blue—and the second-
ary colors fall between
them—magenta, cyan,
and yellow.

There are two big problems with this behavior. Simply setting the
brightest pixel to 100 and the darkest pixel to 0 with all of the intermedi-
ate pixels spread evenly between them does not necessarily provide the
best spread of the tonal range across the most visually important parts of the
image . The other problem is that the image may not need to have either its
brightest pixel at 100 or its darkest pixel at 0.
The first problem is solved with some experience. Great colorists know
tricks that can enhance the perception of an image's tonal range. They
know that they can sacrifice the detail in a certain tonal range where
it may not be noticed so that they can use that tonal range to enhance
a more visually important part of the picture. These are tricks that you
will learn in this chapter and throughout the rest of the topic, Automatic
software doesn't know what is visually important, so it treats all areas of
the image equally.
Even if the image should be spread from 0 to 100, that still leaves
out one critical component: gamma. Spreading out the tonal range really
serves to increase contrast, but the real impression of how bright or dark
the image is relies largely on your gamma or midtone controls. Gamma
really refers to a curve. The reason that midtones are sometimes referred
to as “gamma” is because by lifting or lowering the midtones, you are

valid levels: Levels
that remain legal when
transferred, translated,
or transcoded between
formats.