Tuesday, January 16, 2007
October 2006 HelpLine
Quest For The Perfect Histogram
Q) I've enjoyed shooting digital for the last year. I'm amazed at how many more good shots I get because I don't have to wait for the prints to come back to see how good my exposure was. Now I'm trying to improve my exposure technique. While I understand the histogram somewhat, what should the best histogram look like?
A) I'll make a deal with you. You tell me what the best shutter speed is, and I'll tell you what the ideal histogram should look like. Okay, okay, I'll give you an answer with a little less sass.
But first, a little review. The histogram is a graph that displays the tonal values in the captured image. The left side of the graph represents the darker areas of the image; the right, the lighter areas.
The general rule for evaluating exposure using a histogram is that you should avoid cut-off edges (clipping) on the far ends of the graph. These cut-off parts of the histogram represent loss of detail. For example, if you're taking a picture of a scene with a bright, cloudy sky and your exposure causes the histogram to go up sharply at the extreme right edge of the histogram and quit, you've likely lost detail in the clouds. If, on the other hand, you capture an image in a dark forest and the same sort of clipping appears on the far left edge of the histogram, you've lost detail in the shadows.
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