Nikon D300 User Manual page 152

bottom represent the red, green, and blue color channels, as
can easily be seen. The top, white histogram is not an
additional channel. This is called a luminance histogram, and
it represents an average histogram for the three channels. It is
also known as a brightness histogram. In reality, even though
all the color channels may influence the luminance histogram,
most of its information comes from the green channel. Notice
that they are almost identical.
In digital photography we must use new technology and learn
lots of new terms and acronyms. However, by investing a
little time to understand these tools, we'll become better
digital photographers.
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