Histograms: Free Lesson from Photography 101

Histograms: How to Read Your Camera’s Exposure Graph

The histogram is a simple graph of the light information in your photo, and once you know how to read it, it tells you far more about your exposure than the picture on the back of your camera. In this lesson you will learn what a histogram shows, why the LCD screen alone can fool you, how to bring up the histogram on your camera, and how to use it during a real shoot to make sure your exposure is right.

Every modern mirrorless camera and digital SLR can display a histogram. The buttons differ by brand, but the graph reads the same everywhere.

What a Histogram Shows

1. Read It From Dark to Light

   The left side of the histogram represents the dark areas of your photo and the right side represents the light areas. Everything in between covers the midtones. The taller the graph at any point, the more of your image falls at that brightness.

2. Understand Dynamic Range

   Your camera can’t capture all the detail in a scene. It has a limited dynamic range, the span from dark to bright it can record in one exposure. The histogram shows what was actually captured and when some of the scene’s light falls outside that range.

3. Recognize Clipping

   Clipping happens when highlights are so bright that they hold no detail, or shadows are so dark that they hold none either. If you see a large spike pushed all the way against the left edge, those dark areas will register as pure black in your photo. A spike pushed all the way against the right edge means those areas will be pure white. Clipped detail is lost, so your goal is to keep all of your light information inside the graph rather than piled against either edge.

Why the LCD Can Fool You

4. Use the Screen for Composition

   It is tempting to glance at the back of the camera, decide the shot looks good and keep going. Reviewing images on the LCD is worth doing for composition, but it doesn’t give you enough information to judge exposure, especially whether your highlights are too bright.

5. Don’t Trust Screen Brightness

   The brightness of your LCD can make an image look better or worse than it really is, and in bright sunlight you may barely be able to see the screen at all. It is common to think you nailed the exposure, then open the file on a computer and find it is way off. The histogram doesn’t depend on your screen or your surroundings, so it is the most reliable exposure check in the field.

Display the Histogram on Your Camera

6. Play Back Your Image

   After taking a shot, press the Play button and look at the entire image first.

7. Cycle the Display

   Press the Info or Display button a couple of times until the histogram appears. On a Canon 5D Mark III, pressing Info twice brings it up. Most modern cameras show the picture and histogram on the same screen.

8. Turn On the Highlight Alert

   Many cameras also offer a highlight alert. When it is enabled, any overexposed areas of the image flash during playback. This is especially helpful in bright environments where the screen is hard to read.

Check Exposure During a Shoot

In the lesson, Aaron shoots a high-key portrait outdoors in the middle of the day in the desert in Palm Springs: a white chair, a white backdrop, white pants and a light gray rug. Almost everything in the frame is light, and anything too bright loses its detail. The sun also makes the LCD nearly impossible to judge, which is exactly when the histogram earns its place.

9. Look at the Edges First

   Bring up the histogram and check both ends. If you don’t see any big spikes all the way to the left or all the way to the right, your exposure is in good shape.

10. Leave Room on the Highlight Side

    A light scene should produce a strong spike on the right side of the histogram, and that is fine. What you want is for that spike to sit just under the point of clipping, moved in at least about 10 percent from the right edge. If the spike runs all the way to the right, the image is overexposed and the brightest areas will lose their detail.

11. Adjust and Shoot Again

    The lesson stops at checking the graph, but the fix follows from it: if the graph is crowding the right edge, lower your exposure. If it is crowding the left edge, raise it. Take another shot and check the histogram again until the information sits inside the graph.

This check takes only a second after each shot and saves you from finding a ruined exposure after the shoot. This lesson is part of the Photography 101 course, which covers camera and lens basics in depth.

Key Takeaways

• A histogram graphs the light in your photo, with darks on the left and lights on the right.
• Large spikes against the left or right edge mean clipped shadows or highlights with no recoverable detail.
• Use the LCD for composition, but rely on the histogram to judge exposure.
• Press Info or Display during playback to see the histogram, and turn on the highlight alert in bright conditions.
• For light, high-key scenes, keep the highlight spike about 10 percent in from the right edge.

Quick Reference: Settings and Tips

• Read the graphDarks on the left, lights on the right, midtones in between
• Spot clippingA big spike against the left edge goes pure black; against the right edge, pure white
• LCD screenUse it for composition, not to judge exposure
• Show the histogramPlay, then Info or Display a couple of times (Info twice on a Canon 5D Mark III)
• Highlight alertTurn it on in bright light; overexposed areas flash during playback
• High-key scenesKeep the light spike at least about 10% in from the right edge