How Software Corrects Bad Lighting
One of the most common problems of the amateur photographer is that of the backlit subject without a flash. Here, the camera makes its
adjustments based on the bright background, which turns out perfectly exposed. Unfortunately, because light from behind a subject puts it
(or him or her) into shadow, the subject is left underexposed.152 PART 3 HOW THE DIGITAL DARKROOM WORKS
While use of a
flash would
have prevented
the problem, the
digital darkroom
can provide a
flash fill after the
fact. It treats the
photo like two
photos: one that
is perfectly
exposed and
one that is
underexposed.
To find the two
areas, it calcu-
lates the bright-
ness values of
groups of pixels.1
Areas with a balance of
tones are judged to be
correctly exposed.(^2) Areas that are predomi-
nantly dark are designated
as part of the underexposed
portion.
3