Cinematography 101: How To Read A Histogram

By James DeRuvo (doddleNEWS)

The Histogram is a mystery to some of us, and that’s OK. Like a camera’s zebras and false color (that’s another blogpost), the Histogram is part of a mysterious features inside your camera or field monitor that some cinematographers always wanted to use, but never took the time to understand.

What is a histogram? Simply put, it’s a graph of how your image is exposed, or distributed across the subject and how you can manipulate it to make your exposures even better. By understanding how the histogram works, you can use it to know when your image is too light or too dark. But how do you use it? Well, that’s what this Filmmaking 101 tutorial is all about. But in a nutshell, you just turn it on and watch it react.

Image: Mike Brown

The Histogram is the bell curve of photography, and it’s one of those tools that came to shooters thanks to the digital revolution. When we shot on film, we didn’t have the benefit of the histogram; we had to rely on taking multiple readings with a light meter. But thanks to the histogram, we can use not only a base setting of your light meter to get the shutter and aperture setting to start with, but then we can use the histogram to really dial in the exposure from there.

At its best, the histogram that is perfectly and evenly distributed will provide the best balance of shadow and highlight. Anything that skewed to the right (too much too much white, overexposed) or to much to the left (too much black, underexposed). Stacking to either side will blow out your pixels or make them so dark that you can’t really see the image itself. So here’s a quick breakdown on Histogram 101:

  1. What a Histogram is. A histogram is a tonal distribution. It measures the brightness and darkness of your image and your colors across a range of 256 levels of tonality. That range is broken down from darkest black to lightest white with 254 shades in between. Naturally, if your image is skewed one way or another, being perfectly black or perfectly white, it’ll be unbalanced and either under or over exposed, even if it looks OK to you on the LCD image.  But when you’re out in the field and it’s hard to see the image as it should be on that LCD, the Histogram will be able to give you the information you need at a glance without actually seeing the image itself. Think of it as flying blind on instruments.
  2. What the X Axis is. The X Axis it he base of the chart. It tells the shooter the spread from dark to light pixels. It tells you just how dark or light the image is.
  3. What the Y Axis is. The Y Axis will give you the total number of pixels affected, and what the tonal distribution is, the intensity of it.

Image: Mike Brown

With these values understood, shooters can adjust the ISO, shutter speed and aperture settings to get the desired distribution. Ideally, you want to create a mountain, or as stated above, a bell curve. This will reflect a more balanced exposure of the image and provide the best tonal and color balance with which to edit in post. It’ll also look balanced and more pleasing to the eye.

During editing, you can go into your NLE, such as Adobe Premiere or Final Cut Pro X (or in photography, Photoshop), and open your histogram and begin to slide the midtones up and down, and adjust to balance them out. Once you see that graph, you can use the histogram to remove any spikes in the image and smooth them out.

Now that doesn’t necessarily mean that your mountain needs to be dead center of the histogram. If you’re shooting in bright ambient light, or at night, odds are, you’re histogram is going to lean left or right, even if it’s correctly exposed. But the key here is that it isn’t one of those hockey stick spikes. It’s leaning, sure, because of the ambient lighting conditions, but it’s got a balanced mountain indicating a correct exposure within the context of the light around it.

By contrast, if you’re shooting a subject with a bright background, much like the infamous white ads from Apple, then you’re going to expect the image to have a spike due to the bright background of your image. With a background so bright and white, you’re going to expect a spike from that dominant background. But you will get some midtones gurgling around the bottom, which indicates your image is exposed properly in spite of the dominant white background.

In this instance, you can work for hours trying to balance out that histogram and won’t be able to. From this, you’ll essentially need to make it look as good as it can get. While the histogram will spike, you can manipulate the midtones to the point where even the spike is more gradual. And that’ll help to build your mountain. (Always check your calibrated monitor to further tweak your image.)

So in the end, the histogram is just another tool with which shooters can explore in their DSLR to improve the quality of their image. It doesn’t know ego, it doesn’t know time, it only knows intensity. It can be easily seen, even when you’re outside on a bright day, and can give you a basic idea of just how you’re exposing. I’ve heard of cinematographers and videographers who couldn’t see the image in their monitor because it was so bright, but using the histogram properly allowed them to still capture a great image.

Checking the histogram as you shoot will keep you on track and minimize retakes, or reshoots down the road, due to over- or underexposing.

Hat Tip – Creative Live

About James DeRuvo

James has a multi-faceted career that spans radio, film and publishing. A writer about the technology in the video industry for nearly 20 years, James is also an award winning film director, having garnered a Telly Award for his short film Searching for Inspiration. He's also worked as a producer of many talk radio programs in Los Angeles with topics ranging from entertainment to travel to technology.