While viewing an image file’s information through your camera or computer, have you ever noticed the presence of a small, mountainous looking graph? That little visual—known by photographers as a histogram—actually holds quite a bit of useful information. In the following segment, photographer David Bergman explains:
Simply put, the histogram functions as a means of visually representing the data each pixel of an image contains. It’s a means of quantifying an image and sharing readable information. However, that explanation doesn’t fully describe the purpose or utility of the histogram. The following frequently asked questions provide answers that will better help artists understand just how the math and science behind the histogram correlates to making accurate predictions concerning the contents of an image.
What is dynamic range?
The term dynamic range (in the context of photography) refers to the scope of being able to perceive darks and lights in a single scene. The human eye has an incredibly high dynamic range; we can see very dark shadows and bright highlights all at the same time. However, a camera has a much more limited dynamic range in comparison. The technology is limited, meaning that often times photographers are forced to choose whether they’re going to shoot to expose the brightest parts of a picture or the darkest.
How do you read a histogram?
Although there are no numbers or words that label the axis of the histogram, it’s a fairly straight forward graph to read and comprehend. The graph itself is a representation of an image file’s dynamic range, with pure black lying all the way to the left and pure white on the right. The peaks of a well exposed image will primarily lie in the center of the graph. The more disperse the graph, the higher the overall tonal range of an image. If you find that the histogram is tapering off to one side or the other, it signifies that information is being lost in either the highlights or the shadows of the image.
Why use the histogram?
Although there is no right or wrong exposure for an image, the histogram can be an incredibly helpful tool when trying to determine the exact data an image file contains. The picture on the camera itself can be an inaccurate representation of the true image file due to variable factors internally (such as a calibration issue inside of the Live View screen) or externally (a glare from the sun preventing a clear view of the picture). Therefore, it is possible to see an image that looks completely fine in camera only to realize later on that areas are over or underexposed. Luckily, since the histogram focuses on the data itself, it’s not subject to the same optical variables that prevent us from getting a clear and accurate view of our photographs.
Navigating histograms can be difficult for photographers who aren’t inclined to math or science. The quantification of a photograph often isn’t an easy concept to wrap your head around. However, taking the time to learn the ins and outs of histograms is a worthwhile endeavor for any serious photographer—it could make all the difference in perfecting your imagery in the field to be the best it can be.
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