NEW - Ken Gilbert

NATURE
of the scene is overexposed, it still
appears natural—in fact, it would
look odd if the sun had any detail.
nChange the channel
We’ve been talking about luminosity
(or brightness) histograms, which
combine readings from all three color
channels. But while these work well
for evaluating overall exposure, they
can be misleading.
Take a scene containing a bright
red fl ower. The histogram may show
perfect exposure, since somewhere in
the frame all tonal ranges are found
in one or more of the color channels.
But it won’t tell you that pixels in the
red fl ower may not have any readings
in the blue channel or may have
oversaturated (i.e., clipped) the red
channel. You will get no detail in the
fl ower, even though the luminosity
histogram shows a full range of tones.
For greater insight and control,
most DSLRs today can also show
separate red, green, and blue channel
histograms. The RGB graphs make it
is easy to spot cases when one or two
channels are clipped, and to correct
WITHOUT SPLIT ND FILTER
WITH SPLIT ND FILTER
THERMAL POOL, YELLOWSTONE
NATIONAL PARK, WY
The contrast was too great for the
dynamic range of the camera, so a
2-stop split ND fi lter was used over
the sky to allow for detail in both
the highlights and shadows. Tripodmounted
Canon EOS 5D with 17–40mm
f/4L; 0.8 sec at f/22, ISO 100.
BIRCH LEAF IN FROZEN POOL
The correct exposure according to
the luminosity histogram resulted in a
near-neutral gray. To accentuate the
cool blues, I adjusted the white balance
so that the blue channel in the RGB
histogram was further to the right than
the other channels. Tripod-mounted
Canon EOS-1Ds with 50mm f/2.5 Canon
Macro EF; 0.8 sec at f/22, ISO 100.
accordingly. As with exposure, try to
fi t both tails of each color channel’s
histogram within the scale.
This information is useful if
you plan to convert your image to
black-and-white and discard one of
the color channels. (For instance,
applying a red fi lter effectively
discards information from the blue
channel). In this case you will want
to make sure that the channels you
wish to keep are not clipped.
Reviewing each channel separately
also lets you creatively use color
casts. In the picture of the leaf
(above, right), I increased the amount
of blue to enhance the image’s cold
mood. I did this by carefully adjusting
my camera’s white balance, keeping
an eye on the blue channel histogram
to make sure I pushed it just far
enough without losing detail. p
To see more of Guy Tal’s images, visit
his website, guytal.com.
28 WWW.POPPHOTO.COM POP PHOTO MAY 2009