Histograms are a way to measure exposure more objectively for those who can't see very well. Histograms don't replace your eyes and experience. Histograms are helpful in sunlight where it's hard to see an LCD, or in the shop if setting something exactly. Your eyes are always the final judge.

A histogram is just a guide. Worry about your image more than the histogram.

HISTOGRAM BASICS

A histogram is a graph counting how many pixels are at each level between black and white.

Black is on the left. White is on the right.

The height of the graph at each point depends on how many pixels are that bright.

Lighter images move the graph to the right. Darker ones move it to the left. Easy!

More Pixels

Fewer Pixels

Black - Dark - Medium - Light - White

A Histogram

A good image often, but not always, has a histogram spread all over.

HISTOGRAM HISTORY

Histograms are rocket science. Histograms have been used for automated image evaluation and optimization in self guided missiles for decades. When Tomahawk missiles share America's freedom with millimeter precision, you can thank histograms. Raytheon calls this "Digital Scene Matching Area Correlation," or DSMAC. This all used to be classified.

You are smarter than a histogram. Use them as guides, not Gods.

COLOR HISTOGRAMS

Color histograms (page 83) are required for color digital photography. Many cameras lack these. I cover this later (page 83). If your camera only has a single histogram, like the Nikon D70s, D1X or Canon 20D, ignore the histogram! Single histograms are dangerously

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