The Value of a Histogram

This is less a rant or even a clarion call. Think of it as a peer review…
...concerning Histograms.

“When you can measure what you are speaking about, and express
it in numbers, you know something about it.”- Lord William Thomson Kelvin (1824 -1907)

Lord Kelvin, scientist, philosopher and extraordinarily curious man.

But relating to photography, I say yes and no to his premise. Yes, I can express what I shoot
in numbers, but no – a graphic display of any given image is just that and cannot be construed
as being anything other than a dubious post mortem chart. However, there is one exception, and
that is the “Characteristic Curve”. A histogram is not a “Characteristic Curve”. This short series will
try to make sense of and interrelate waveforms, curves, the zone system and histograms.

A histogram is a metric looking for a friend.

We’ll start first with these 3 images and their histogram value. To me, the informational content of this
system may only be of value in these 3 histograms. Though, specifically the 18% gray panel with
respect to calibrating a meter. Shoot a gray card and if the lines spike in the middle of a histogram
then your meter is good. If the line falls to either side of the middle, then an adjustment is required.

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