Of these temperatures, the ones most commonly affecting photography are the temperatures of outside light, ranging around 5500K, and
those from inside, artificial lighting, around 3200K. The lower temperatures tend to have a redder, warmer tint that gradually changes to
a bluish tint at the higher temperatures. As a consequence, photos taken indoors with film designed for outdoor use or taken digitally with
a camera set to expect outdoor lighting have a warm, orange discoloration. Photos taken outdoors with either film or a digital imager
expecting indoor lighting are cold and bluish. The pictures of Daffy were shot without color correction, left to right, in fluorescent light,
daylight, and incandescent (tungsten) light. The spectra show how colors were distributed in each photo.3
In film photography, there
are three ways to counter the
inconsistency of light: film
designed for outdoor or for
artificial lighting, lens filters
that temper the light with
colors that balance out the
inaccurate hues of outdoor
or indoor light (filters can
also be used in the dark-
room, but relatively few
photographers do their own
color film printing), and a
flash unit that gives outdoor
colorations to indoor scenes.4
The fixes for film photography require some degree of planning, and
they are tricky to accomplish given all the possibilities for false whites.
Digital photography can correct for off-white lighting on an ad hoc
basis by changing a setting for white balance. On some digital cam-
eras, the process of setting white balance is accomplished by giving
the camera an example to go by. The photographer merely presses a
certain button while pointing the camera at something known to be
white (despite our human tendency to interpret many different hues of
white as being identical). This is similar to taking an exposure meter
reading by pointing the camera at something known to be a medium
gray. But the two types of readings are measuring different qualities of
light around your subject matter, and taking one measurement does
not replace your need to take the other measurement. White balance
can also be set by dialing in a specific Kelvin temperature or a precal-
culated setting for common situations such as indoors or candlelight.5
The camera’s software notes the ratio of red to blue pixels in the
white example. (Green does not have a significant effect on white
balance.) If the ratio doesn’t match the usual proportions of red
and blue for a white object in normal daylight, the camera’s
processor adds more red or more blue pixels to the image to
correct the color. Subsequently, when a photo is snapped, the
processor makes the same red/blue adjustments to it.6
Should small lighting changes occur without the
photographer noticing and resetting white balance,
a digital photo’s white balance can often be easily
adjusted later using photo-editing software.7
CHAPTER 5 HOW DIGITAL EXPOSURE SIFTS, MEASURES, AND SLICES LIGHT 79