Understanding Your Digital Camera's Histogram
by Digital Darrell

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IN CONCLUSION

Most digital cameras have a rocker switch of some sort that is used to scroll through the images you have already taken. Most of these rocker switches will be pressed up or down to scroll through the images, and then left or right to select various informational modes, such as the histogram mode. So, when you take a picture of an important subject, use the little thumb rocker on the back of most digital cameras to select the histogram view of your image. (Check your manual, if you can't figure it out)

Your camera meter will be used to get the initial exposure only. Then you will look at the histogram, and see if the image's light range is contained within the limited range of the sensor. If it is clipped off to the right or the left, you may want to add or subtract light with your +/- EV compensation button, or use your manual mode. Expose for the light range with your histogram. Let your light meter get you close, then fine tune with the histogram.

In Figure 7 above is an actual histogram as seen on the back of a digital SLR. Note that the histogram is not clipped on either the dark or light sides. The yellow histogram graph is well centered, so the image is well exposed.

Notice also that there is not much mid-range in this image (Figure 7). It is rather high-key, since it is a direct flash shot with a light background. See how the histogram shows this by peaking the mountain range very sharply in the lighter side of the histogram window. The tallest peak is probably a representation of the white background, while the smaller peak to the right is most likely a representation of her skin tones. The young lady's hair is mid-range to dark, so you see a smaller peak to the left side. See how nice it is to be able to use the histogram to control your exposures?

Most of us will try to expose for the bright light, since our eye craves to see detail in the light areas, but could care less about detail in the dark areas. Keep your histogram's bright light values side from being clipped off, but get it really close, and your image will probably look a lot better. If the light is too contrasty, then you must resort to filters and reflectors, or overcast skies, like in the good old film days.

There are other LCD viewing modes that you can use along with the histogram graph, such as the blinky blinky mode for blown out highlights, which most digital cameras have today. What this does is to blink from light to dark in the blown out highlight areas. This is a rough representation of a highlight-value clipped histogram, and is quite useful for quick shooting. Using your camera's light meter, histogram, and the highlight burnout blink mode together is a very powerful method to control your exposures. If you master this method you will have a very fine degree of control over where you place your image's light ranges. This is sort of like using the famous Black & White Ansel Adams "Zone System," but it is represented visually on the LCD of your digital camera.

You can even use your histogram to imitate your favorite film type. For instance, let's consider transparency film. It is limited to only a few stops of light and is very sensitive to overexposure. A digital sensor is somewhat similar. So, if you use the histogram to expose "for the light" side of the graph, not allowing blowout (clipping) of light detail, and then you ignore the left side of the histogram graph, allowing the dark values to fall where they may, you will achieve a look very similar to a well exposed Fuji Provia® slide. Then, if you take the image into your computer and boost the saturation of the colors a bit...you now have achieved a super-saturated Fuji Velvia® look.

Your histogram is a very valuable tool, and this article just touches on its capabilities. There are many discussions out there about how the histogram represents a combination of the three RGB channels (Red-Green-Blue), or only the green channel of the three in the RGB, or even only a combined luminance channel. It varies according to the camera. Your manual will tell you what type of histogram your camera has, if you are interested.

The manipulation of the histogram "levels" in Photoshop® is a detailed study in itself. Learn to use your computer to tweak your images, and you will be able to produce superior results most of the time. But, first learn to use your histogram to capture a nice image in the first place!

Your histogram is simply a graph that lets you see at a glance how well your image is contained by your camera. Too far left, and the image is too dark, too far right, and the image is too light. Learn to use the histogram well, and your images are bound to improve!

Keep on capturing time...