Learn to read your exposure
Use histograms to protect image detail
The histogram is an incredibly useful tool for checking the exposure of your image, but it’s often overlooked for fear of it being too technical to understand. At its most basic, it maps the distribution of tones in an image, and peaks in the graph illustrate whether your photo is predominantly shadows, highlights or mid-tones. After you take a picture it’s typical to review it on the back of your camera, but as the brightness of LCD screens greatly varies, it can be hard to see if areas of your shot are slightly under or overexposed. The best method for exposing accurately is to check your histogram, as it clearly shows whether you need to darken or lighten the next image you take. In this tutorial we’ll show you how to do so, both in-camera, and afterwards in post-processing, so that your shots capture the full range of tonal detail.
There’s no such thing as correct exposure, because ultimately it’s a creative choice, and there are certain shooting styles, such as high key, where a skewed tonal range is desirable. For genres like landscapes however, where an even balance of tones and luminance is required, the histogram should ideally appear as a bell-shaped curve. Understanding your histogram is a great way to make sure you’re recording a scene correctly, and using it needn’t add extra time to your workflow.
Choose graph type
Most DSLRs offer the choice to display either a brightness or a colour (RGB) histogram, selectable from the Playback Menu. It’s generally best to start by choosing Brightness, as this will provide you with one graph that’s easy to interpret.
Take a test shot
Position your camera, turn on Live View, and set it to exposure simulation. On many cameras you can press info to bring up the histogram on screen as you shoot. Take a test shot so you can evaluate the exposure.
Review and adjust exposure
Press the Playback button to check the resulting histogram. If the image is too dark the graph will be skewed to the left, and if it’s overexposed it’ll be biased to the right. Apply exposure compensation accordingly, or adjust settings manually.
Retake the shot
Shoot the scene again and review the histogram. If a certain portion touches either edge, it indicates a loss of detail. Ensure that your graph is roughly central, and there’s a good distribution of tones across the range from left to right.
Open your final image in Photoshop, then go to Window>Histogram or click the Histogram tab to view the Histogram panel. Set the channel to Luminosity, to display a histogram representing the luminance or intensity values of the image.
Refer to the histogram when changing the exposure of your image. Go to image > adjustments > curves, and tick the histogram option to see the graph displayed. Add nodes to the line, and drag it until your shot is correctly exposed.