Histograms: Secret for Perfect Exposures

histogram-sampleYou can’t trust your camera’s display screen. We’ve all thought we had great pictures and gone on to do other things, only to find out later on that the shots don’t look so good when printed or seen on a computer. This is because brightness of the display screen is adjustable and if it is set too bright an underexposed photo will look OK. If it’s set too dark you won’t detect overexposed images. The good news is that it’s easy to get perfect exposures with histograms and your manual will tell you if your camera can display them. Some cameras show them while you are composing your shots, some only display histograms of pictures you have already taken. Either way, this is a terrific tool for getting photos that look as good as you as whatever you photographed did.

I took some candies from the glass and counted how many of each color were in my sample. Just as I collected information about the colors of the candies in the glass, your digital camera collects information about what sort of image you’ll get (or got) with your camera’s exposure settings. Candy Color Histogram When I put my results on a graph, I was making a histogram — a graphical representation of how often something occurred. Most digital cameras can create and display a histogram depicting the distribution of brightness measurements. If you are setting up a photo, the histogram tells you about the brightness in the scene you are photographing. A histogram of a photo you’ve already taken depicts the distribution of brightness values in the photo. It doesn’t tell you where the light and dark spots are; it just reports how many pixels have a given level of brightness.
histogram-good-exposure Histograms put information about dark areas of the photograph on their left side, info about bright areas is on the right side, and intermediate values are in between the two. The well-exposed picture at left has a broad range of brightness values and that causes the histogram to be somewhat flat with many of the brightness measurements falling in the center region. The large number of measurements shown at the left border of the histogram are from the dark areas of the arch.

histogram-underexposureCompare the first picture with the underexposed version at left and notice how there are far more measurements on the left of the histogram.

histogram-overexposure
The next picture is overexposed and it’s histogram has many more counts on the right side than the other two versions.

Having a lot of the measurements piled up on either side of the histogram is not good, but it is better to be underexposed than overexposed. Editing programs can correct underexposure unless it is severe, but overexposure can’t be fixed, so steer away from overexposure if the histogram has many counts jammed up against the right edge. Increase shutter speed, decrease the ISO setting or aperture size (smaller f-number), or adjust exposure compensation. The links will take you to more information about these options.

Exposure – Speed, Aperture, and ISO Simplified
Exposure Compensation – the Goldilocks Factor
All About Apertures: f-stop Mystery Solved and Explained!

It can take a little practice to get comfortable using histograms, so I’ll talk about them some more tomorrow and suggest a few short exercises to get you on your way.

As always, comments and questions are welcome. I hope to see you here again soon and may your light be right.

Curtis

© 2011, TheDigitalPhotoCoach.com. All rights reserved.

© 2011, TheDigitalPhotoCoach.com. All rights reserved.

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