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1

The Histogram – A Primer

by Christopher B. Derrick

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I’m sure that you’ve ran across the histogram when cycling through your digital photos while still in the camera, but more so when you bring your images into a post production workflow – like Lightroom or Photoshop. 

Just what exactly is the histogram?  The histogram is a graph that displays how the tone is laid out in your image (from left – black to right – white), such that the higher the peak at any given point on the histogram the larger number of pixels of that tone are present in your image (it pays to familiarize yourself with the histogram while looking at a B&W photo, and then transfer your understanding to a color photo).  So when your image contains a strong amount of black or darker tones (like a night shot), the graph will have a higher curve on the left-hand side of the graph, and then the converse is true for light and/or white tones (like a snow scene).

The histogram will enable you to check the exposure of your image right after you’ve taken it, instead of getting home and noticing that it’s underexposed or overexposed.  The LCD screen might not be able to give you a fair judgment of your photos exposure, so use the histogram to make the determination to take another photo with a different exposure settings (aperture, shutter speed, ISO).

While there is a baseline of acceptable exposure, we can all agree that there is a wide range of what falls under the rubric of “art” when it comes to a photos exposure.  What you do want to watch out for is severe spikes or gaps on the graph in the deep black or deep white sections, because those sections indicate that there is missing image information that you can’t bring back in the post process. The spikes and gaps directly indicate where you are lacking image detail… now maybe you want this (say with a silhouette), but you want to know that exactly.  Because during the printing step, you want to know that you can replicate the image as accurately as possible.

The histogram gives you an opportunity to understand a different element of your photograph, so you can achieve the true results (and effects) that you want from your photos.  By fully understanding how the histogram works, you can guarantee that your photographic results will be greater. 

The big benefit of understanding how the histogram works is when you’re doing adjustments in Photoshop (or another comparable image editing program), and you can target not just the tonal values, but you can adjust the color intensity more specifically this way.  Incidentally, many on-camera histograms display the RGB histogram curves, so you can see how the various primary colors are recording — this is beneficial, too, but a further discussion of the intricacies of the histogram is required.  It’s all about achieving the image that you precisely want/see in your head, and the histogram is just another tool that will help you on your journey to photographic artistry.

Chris Derrick is a writer, photographer, screenwriter and director living and working in Los Angeles. He studied film production and screenwriting at the University of Southern California, and continued to expand his photographic knowledge through classes at the Art Center College of Design.

Website: shadowboxercinema.net

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1 Comment

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  Markku said:

  To be exact, there are 4 histograms, R, G, B and combined. Depending on the picture composition, you should follow more that just combined one to fully utilize the sensor.

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