Nikon D300 User Manual page 663

Then look at the right side of the histogram graph and note
that it is not completely against the right side, although quite
close. The image contains all the light values available.
Everything in between is exposed quite well, with full detail.
A histogram does not have to cover the entire window for the
exposure to be fine. When there is a very limited range of
light, the histogram may be rather narrow.
The image in Figure 9-16 is a relatively bland image with
smooth graduations of tone, so it makes a nice smooth
mountain-peak histogram graph. This will not occur every
time, since most images contain quite a bit more color
information. Each prominent color will be represented with
its own peak on the histogram graph. The most prominent
colors will have higher peaks, while the less prominent will
have lower or no peaks.
As we progress into images with more color or light
information, we'll see that the histogram looks quite different.
Look at the image in Figure 9-17. This is from an image that
exceeds the range of the D300(S)'s digital sensor.
Notice that, overall, this image is dark and looks
underexposed. The histogram in Figure 9-17 is crammed to
the left, effectively being clipped off. There are no gradual
climbs like on a mountain range, from valley to peak and
back to valley. Instead, the image shows up on the left side in
mid-peak. It is clipped. This is an underexposed image and
the histogram reflects that well.
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