Exposure may be the most common problem in photography. Whether your image is underexposed (too dark), overexposed (too bright), or just washed out in a hazy low-contrast fog, improper exposure can ruin an otherwise good shot.
Even though many basic photo-editing programs provide “Brightness” and “Contrast” controls for tweaking exposure, I prefer to use Photoshop’s Levels tool, because it provides more precise fine-tuning, and it gives you separate control over the shadows, highlights, and midtones in your photo.
You can access the Levels tool in Photoshop under Image > Adjustments > Levels — but I don’t recommend doing it that way.
Instead, I always prefer to make a Levels Adjustment Layer.
By creating an adjustment layer, you preserve the option of revising the adjustment later or changing its opacity. An adjustment layer also comes with an attached Layer Mask — in case you want to apply the adjustment to only part of the image (that’s a separate topic for another time).
Suffice it to say that making a Levels Adjustment Layer, instead of just choosing Adjustments > Levels, gives you much more flexibility and control.
To quickly create a Levels Adjustment Layer, click on the Adjustment Layer button at the bottom of the layers palette in Photoshop. Then pick Levels from the drop-down menu.
In the window that opens you’ll see a Histogram representing the range of dark and light pixels in your image, with black at the left and white at the right.
Below the histogram are three sliders for setting the light values in your photo. From left to right they represent the Black Point, the Midpoint, and the White Point respectively (highlighted in pink on this image.)
This histogram is typical of a washed out, low-contrast photo. You can see that the “black” or left edge of the histogram curve does not reach the left edge of the box, and the “white” or right edge of the histogram does not reach the right edge of the box.
In an ideally exposed photo, we usually want to take full advantage of the entire light/dark range available to our cameras and our eyes. In other words, we want the brightest pixels in our image to be pure white, and the darkest pixels in our image to be pure black. In a photo like this one, they instead range in tone from dark gray to light gray, making it a low-contrast image.
To quickly correct the tonal range of the image and expand it to take advantage of the full light/dark spectrum, simply drag the Black Point (leftmost) slider to the right until it touches the edge of the histogram curve. Then drag the White Point (rightmost) slider to the left until it touches the edge of the histogram curve. When you click “OK” it tells Photoshop to re-map the light values in your image so that the darkest pixels become black and the lightest pixels become white, and the rest are spread appropriately in between.
We’ll call this the “standard adjustment” to Levels. It’s the most common starting point for exposure adjustment. Of course, your eye must always tell you whether it’s right for any given image or not.
In the photo here, while this standard adjustment is a big improvement, I want to go further, because I want to bring the animal’s face and eyes out of the shadows and make them the focal point of the image.
To brighten the midtones of the image, I move the Midpoint Slider (the center slider) to the left. This adjustment brightens the face and eyes of the monkey, pulling those details out of the shadows. (This is a helpful adjustment on photos where you wish you had used fill flash.)
Now, however, as a result of brightening the midtones, I have lost most of my blacks. So I decide to pull the Black Point slider even further to the right, well inside the curve of the histogram. And likewise, I decide to pull the White Point slider farther to the left, well inside the edge of the histogram curve, in order to make the highlights pop out a little more.
When you move your black or white point inside the curve your histogram like this, you are “clipping” your shadows or highlights and losing some detail in those areas. You are essentially telling Photoshop “treat every pixel darker than this as pure black” or as pure white on the highlight end.
Photoshop provides a neat trick to allow you to see exactly where your shadow or highlight clipping begins. Just hold down the ALT key (PC) or Option Key (Mac) as you drag the slider, and when you see color starting to appear, that indicates pixels where shadows or highlights are getting clipped.
This can help you decide when, and how much, you are willing to lose detail in shadow or highlight areas to improve exposure in other areas.
This kind of adjustment can only be done by trial and error. Beyond the “standard adjustment” there are no hard and fast rules, you simply look at your photo and adjust until you get the look that you want.
In this case, you can see in the final histogram that I have placed the Black Point, White Point, and MidPoint sliders to increase the overall contrast and bring out the eyes and face of the animal, at the expense of losing some detail in the highlights and shadows.
All of this took just a few seconds in Photoshop.
And because I used an adjustment layer, I can come back later, if I change my mind, and alter this Levels adjustment retroactively. To do that I would simply double-click on the Adjustment Layer icon found on this layer in the Layers Palette (highlighted in pink in this image).
While it’s a little more complex than using the “Brightness” or “Contrast” controls found in many photo-editing programs, I hope you can see now why the Photoshop Levels tool is an easy and powerful way to adjust exposure.
About the Author: Phil Steele is the founder of SteeleTraining.com where you’ll find free tutorials on photography, Photoshop, Lightroom and more.
If you are interested in off-camera flash photography you may want to check out his online course “How to Shoot Professional-Looking Headshots and Portraits on a Budget with Small Flashes.”