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Home    Lesson Plans    #5: How to read a Histogram

How to read a Histogram

When you have even lighting and your photograph is correctly exposed, you would normally get a histogram similar to Figure 1 below.

The histogram of the photograph in Figure 1 has a peak in the middle and evenly tapers off into the left and right of the graph. This means that the photo has evenly distributed shadows and highlights. If your image contains mostly a single tone of midtone colors like green, blue, brown and in this particula photo, grey, then you would get a histogram similar to the one in Figure 1.

Even Lighting Photo Histogram
FIGURE 1: Photo with even lighting (F/8, 1/10 sec., ISO 100)

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Low Key and High Key Photos

In some cases, when your photo is dominated by light or dark tones of colors you will produce what are called High Key and Low Key photos respectively.

Low Key Images. If your photo consist mainly of dark tones and colors, the histogram will show valleys and peaks on the left side of the histogram. As long as your image is properly exposed, you should not have a clipping on the left of the histogram. Remember how I stressed in the previous page that you need mostly concern yourself with clipping. The example photo in Figure 2 below is a Low Key Image but it is correctly exposed. You can still tweak this image using your photo editing software without losing any detail in the shadows.

Histogram of a Low Key Image
FIGURE 2: Low Key Image Histogram (F/3.5, Shutter Speed: 1.6 secs., ISO 100)

High Key Images. Obviously, High Key images are the opposite of Low Key images. If you photo is dominated mostly by light tones of colors, your histogram will display its valleys and peaks on the right side of the histogram. Again, as long as the photo is not overexposed, you should not see any clipping on the right end of the histogram. An example is shown in Figure 3.

Histogram of a high key photo
FIGURE 3: High Key Image Histogram (F/8, Shutter speed: 1/1.3 secs., ISO 100)

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Assignment 5: Understanding Histograms

Take out your DSLR camera and take lots of photos and examine their corresponding histograms.

Assignment Instructions

  1. Set your camera to any of the manual modes (Aperture Priority, Shutter Priority or Full Manual mode)
  2. Pick a scene with a singular color tone and try to produce a histogram that peaks at the center and gradually tapers off to both sides. See the example photo in Figure 1. I am not going to tell you specific colors. I would like you to find it out for yourself. Which colors produce this type of histogram?
  3. Next, find a subject or scene that has mostly dark tones of colors. Make sure that your exposure is correct (use your camera's light meter) and shoot away. Examine the histogram of these photos. What does the histogram look like?
  4. Next, find a spot where your scene comprises mostly of light tones. Again, use your meter to expose the scene properly and shoot several photos. Examine the histograms. What does it look like?
  5. Next, find a spot or scene with a wide variety of tones and colors (from light to dark). Again, use your meter to expose the scene correctly and take several shots. Examine the histograms. What does it look like?
  6. Now, purposely take photos that are under or over-exposed and examine their histograms. Which end of the histogram did the valley or peak clip?
  7. Now, change your aperture setting to say, f/8 and take a picture of your subject again.
  8. Next, change your aperture setting to its smallest opening. In other words, set it to the highest f/stop number, for example, f/22. Take a photo of your subject again.
  9. Lastly, examine the histograms of the photos you took and try to determine which part of the image does the valleys and peaks refer to? Remember how I explained in the first page of this lesson how the height of the peak pertain to the total amount of a particular color?

It would be best to download your images onto your computer and examine the histogram using your photo editing software. However, the quickest way to examine them is through your camera's viewfinder. Check your camera's manual to learn how to open up the histogram so you can view it immediately after you take a photo.

Project 365 or 52 Week Project for the serious hobbyist

If you are really serious about learning photography then I highly recommend that you try Project 365 or 52 Week Project. Both of these projects are great ways to practice and learn photography. For more detailed information about these projects and how to start, read my Project 365 or 52 Week Project blog. I have carefully organized a Weekly Theme Suggestions for this project to coincide perfectly with our step by step Lesson Plans.

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