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iPhoto ’11: The Macintosh iLife Guide to using iPhoto with OS X Lion and iCloud by Jim Heid, Michael E. Cohen, Dennis R. Cohen

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Reading a Histogram

A histogram is a bar graph that shows how much black, white, and mid-tone data a photograph has. Pure black is on the left, pure white is on the right, and the mid-tones are in between. iPhoto displays a color histogram that breaks this information down into an image’s three primary-color channels: red, green, and blue.

Beneath the histogram is a set of sliders that let you change what iPhoto considers to be pure black, pure white, or mid-tone values.

A Sampling of Histograms

This properly exposed shot has a good distribution of dark, bright, and mid-tone areas.

image

This overexposed shot has very little data in the blacks; everything ...

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