Graphics Reference
In-Depth Information
D e f i n i t i o n
tonal range (singular):
The tonal range is the
difference between the
brightest and darkest areas
of the image, sometimes
also called the dynamic
range, luminance range,
or contrast range, though
these terms can have
slightly different technical
definitions. The tonal range
of the image—and how
those tones are spread
throughout the tonal
range—defines its con-
trast. For some applications
of this phrase, tonal range
indicates the actual num-
ber of levels of tones that
a recording medium can
record (256 per channel in
the case of RGB 8-bit, or
1025 per channel in the
case of RGB 10-bit). For our
purposes, we will refer to
tonal range (singular) as
the range of tones between
brightest and darkest. Ansel
Adams and other propo-
nents of the Zone System
break the tonal range of an
image into 11 distinct tonal
ranges.
Automatic Corrections Are Bad
Let's run an experiment to show that you are already a better colorist than the automatic
color correction tools available in most software packages. Even if you aren't tempted to
use these automatic features, this little experiment is an important lesson in using your
eyes instead of the numbers or doing things technically perfectly.
Open the “Artbeats Popcorn” image (from Artbeats' beautiful Food1 collection;
Figure
1.3
) in any application that allows you to automatically color correct. Most of these tools auto-
matically spread the tonal values and “white balance.” But because these tools don't know
what the image actually looks like, they do everything by the numbers. Sometimes using
them can get you in the ballpark very quickly, and sometimes it makes an image look worse.
For my example, I brought the popcorn QuickTime into Avid Xpress Pro and color cor-
rected it using the automatic color correction tools. To be fair to Avid and other applications
with these tools, these automatic corrections can sometimes do a pretty good job. If you're
in a rush, give each image a shot with them, but be prepared to take matters into your own
hands. Doing things manually is actually a good thing. If all someone needed to do was
push a button, then there'd be nothing special about the skills you're trying to develop.
Anyway, after running the popcorn image through the auto color correction, it
doesn't look nearly as appetizing as the beautifully color corrected original image.
Most of these tools figure that you want something that's pretty “white” or neutral-
looking and with a tonal range that's completely spread out. In the case of the popcorn
image, the image needs to have a nice, warm golden tone. Also, the original image
doesn't really go much beyond 80IRE in brightness, yet the autocorrection spreads the
tonal values over the entire range, which causes the steam rising from the popcorn to
take on a harsher feel and the brighter parts of the popcorn come close to clipping out,
destroying detail by overexposing (
Figure 1.4
). (See definition of clipping on page 22.)
tonal ranges (plural):
The three commonly used
tonal ranges that are
used to break down the
description (and control)
of an image are shadows,
midtones, and highlights.
Sometimes shadows are
referred to as blacks,
pedestal, set-up, lift, or
even lowlights. Midtones
are often referred to as
gamma, but also as grays
or mids. Highlights are
sometimes also referred
to as whites, gain, luma,
or even video. These are
Fig. 1.3
Original image courtesy of Artbeats' Food1 collection.
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