Graphics Reference
In-Depth Information
CHAPTER 1
Range Primer
Color correction is generally broken down into two distinct processes: pri-
mary and secondary color correction. These two processes will probably
always be referred to as two
distinct
processes, but the technology itself is
starting to change the perception of how and why these two processes are
used and when the colorist moves from one process to another.
Primary color correction is the process of setting the overall tone, contrast,
and color balance of the image. Secondary color correction is an additional
step that refines the image in specific geographical regions of the image or
in specific color vectors of the image. Don't let that word “vector” scare you.
There are a number of definitions of the word “vector” that are used when
discussing color space. It basically means the specific location or coordinates
of a color. A vector can also mean the direction that something is heading,
from one point in space towards another. So, essentially, in the color correc-
tion world, “vector” is just the technical word that defines a specific “color.”
Think of a vectorscope, which is a tool that allows you to kind of see the
“color wheel” (
Figure 1.1
)
. The vectorscope shows you where parts of the
picture are on the color wheel. So the vectorscope shows you the vector—or
location on the color wheel—for the elements of your video image.
The first step in any color correction is to assess the tonal range of the
picture. What are the problems with the tonal range and how can you
address them? From a purely technical standpoint, it seems like an easy
question to answer. As a matter of fact, many color correction plug-ins
or color correction systems built into nonlinear editors have “automatic”
buttons that will attempt to spread out the tonal range for you based on
purely technical information. These automatic systems assume that the
brightest parts of the picture should be as bright as possible while remain-
ing “legal.” The darkest part of the picture is also set automatically to be
as low as possible while remaining “legal.”
D e f i n i t i o n
legal:
For video-based
images, “legal” means that
the brightness and color
saturation of an image
does not exceed minimum
or maximum levels that
have been determined for
a specific delivery channel
for a video. This usually
implies broadcast, but can
also pertain to duplica-
tion. Each duplicator or
broadcaster sets their own
specific requirements for
video levels, but in general
these levels adhere to
national and international
standards and describe that
the darkest portions of the
luminance of the picture
can not fall below 0IRE for
NTSC digital video (and
most other international
video of any type) or 7.5IRE
for composite NTSC in the
United States. The bright-
est pixels are not to pass
100IRE when monitoring
luminance only or, when
combined with chroma,
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