Digital SLR Photography All-in-One For Dummies, 2nd Edition by Robert Correll

Author:Robert Correll
Language: eng
Format: epub
Publisher: John Wiley and Sons, Inc.
Published: 2013-03-12T16:00:00+00:00

Figure 5-16: This histogram charts brightness.

Combined RGB histograms chart brightness by creating separate color channel histograms (red, green, and blue) and adding them together. RGB histograms aren’t weighted. Each channel is as important as the other. The problem with this approach is that each pixel’s spot in the histogram is skewed toward the strength of any one of three component colors, not by the perception of its brightness. In other words, a pixel that’s close to blowing out the red channel will show up as very bright, even if the green and blue components are next to nothing.

Therefore, combined RGB histograms are better at showing you if any of the three color channels are clipping, not the photo’s perceived brightness. To know which channel(s) is in danger of being overexposed, you must examine the individual color channel histograms.

You may also see combined RGB histograms referred to as three-channel RGB histograms or even RGB histograms. The latter can be confusing, as color channel histograms can collectively be referred to as RGB histograms.

Color histogram

These histograms chart the brightness or saturation in each color channel (red, green, and blue). An example is shown in Figure 5-17. Saturation describes a color’s purity or vividness. The less vivid a color, the closer to gray it is. When it becomes gray, the pixel has no color information — it’s completely desaturated. When the color (red, green, or blue) is more vivid, it becomes brighter, cleaner, and more vivid. When it’s as bright as it can possibly be and there’s no place for it to go, it’s fully saturated.

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