Beginning Waterfall Photography :: Histogram


Have you ever come home from a beautiful day in the backcountry or on the Blue Ridge Parkway, excited to see the pictures from your amazing day, only to find that none of them turned out well? Blue skies washed out into white. Intricate streams of water cascading down a rock face turned into a glowing blob. You can often spot these and other exposure problems in the viewfinder, although it may require a time consuming search of the image while zoomed in. There is a much faster way to know exactly how the camera recorded the image at a glance called the histogram.

A histogram is a graph that shows how the camera sees a picture. This is important because your camera and its various lenses have different limitations and optical characteristics than the human eye. You can use the viewfinder to check your exposures, but the histogram is both faster and more accurate.

What is a good exposure? In truth, any picture you like is a good exposure. But for the purposes of this article I will assume you usually want the same thing I usually want: an evenly exposed photo that does not lose detail either in the brightest parts or the darkest parts. It is important to understand that in the world of digital photography, when you talk about "losing detail" that means the information is not available in the image file and no amount of post processing can bring it out. You may be able to synthesize detail in Adobe Photoshop or something similar, but the original detail at the time of capture is lost. So it is extremely important that your digital exposures do not lose detail in their darkest or brightest areas.

A histogram is a graph that shows the brightness values (from pure white to pure black, and all the levels of gray in between) recorded by the camera for an image. Each image has its own histogram, and you can tell important things about what the camera recorded with just a glance at the histogram. Adobe Lightroom labels the histogram in 5 sections. The far left side is pure black. As the graph moves right it shows values for lighter and lighter shades of gray until the right side shows pure white. You can probably extract amazing information from this graph, but I really just use it to answer the question "Did I lose any detail?"

To check your exposure using the histogram, simply look at its left and right edges. The right edge shows pure white. If the graph does not extend all the way to the right edge, you have not lost any detail in the highlights. Next, look at the left edge. The left edge shows pure black. If the graph does not extend all the way to the left edge, you have not lost any detail in the shadows.

Example One: A well exposed photo

This picture has been processed in Adobe Lightroom, and it shows what a well exposed histogram might look like. There is a distinct gap at the right edge of the graph, indicating that none of the highlights are being clipped in the picture. This is the most important thing to check in waterfall photography! There is nothing worse than getting home from your trip to find that your pictures could have been great if you had not overexposed them! Not all well exposed photos will have a histogram that looks exactly like this one. It is very dark in some areas, like the overhang on the far bank. And it is very bright in some areas, like the water in the rapid. This makes its histogram reach almost to both edges, using the entire available dynamic range. Not all pictures will or should have this much variation in brightness.

Example Two: Overexposed

This picture shows a common problem in waterfall photography. The picture is exposed correctly except for the sunlight falling on the water. The right side of the histogram extends all the way to the right edge, which lets me know the camera was unable to capture detail in the brightest parts of the image. This is what water looks like when it is overexposed. It loses the fine details and becomes glaring, ugly white instead.

This picture has some pure black in it as well, but it is normal for our eyes to see pure black in our environment. So in this case the area beneath the boulder in the foreground looks natural even though there is an area of pure black.

Example Three: Underexposed

This picture shows the opposite problem, an underexposed photo where the shadows disappear into blackness. Notice how the left edge of the histogram extends all the way to the edge. Underexposed shadows are more natural looking than overexposed highlights, so you may find this to be acceptable more of the time.

On Canon cameras, switch to Live View, then use the Info button to cycle through info modes, one of which includes a live histogram. You can also use the info button when looking at pictures on the camera to show the histogram. Consult your camera manual for other camera manufacturers. Not all cameras can display a live histogram, but most will have the ability to show the histogram of an image after you shoot it.

From now on, make sure you check your histogram quickly after each shot you take. Check both edges to make sure you are not losing detail in the highlights or shadows of your picture. If you are losing detail, change the exposure settings on your camera and take another shot. With a little practice the histogram will allow you to evaluate the exposure of a photo at a glance, even in situations like bright daylight where the viewfinder can be difficult to use.

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