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Use the Threshold command to restore overexposed photos

by Jim Whitcomb

Application(s): Adobe Photoshop CS2/CS3/CS4/CS5

Operating System(s): Microsoft Windows, Macintosh

At A Glance:
Nobody likes a photo that doesn’t turn out just right, but as an avid Photoshop user you know that you can often fix those errors! We’ll show you how to use the Threshold command to restore exposure problem areas in your digital photos.
To salvage your overexposed images, we’ll:

• Discuss what overexposure means.
• Go over how the Threshold command affects an image.
• Use the Threshold command to isolate the highlight areas in an image.
• Select, copy, and paste the highlight areas into a new layer.
• Adjust the highlight tonal level to add detail to the highlight areas and then examine the results. 

It’s great to sit and run through a thumbnail gallery of new photos, but excitement can quickly turn to disappointment when you view an enlargement of what you thought would be a great photo and then notice that there isn’t much detail in the highlight areas due to overexposure. Before you give up and reach for the delete key, reach for Photoshop’s Threshold command instead. It will surprise you to see how easy it is to restore your washed-out images.

Understanding overexposure

When you go from inside a dimly lit room to outside in the sun on a bright day, you probably squint for a few seconds until your eyes adjust to the light. While you’re waiting those few seconds, just about everything you see looks bright white, much the same as overexposed areas in a photo. Actually, everything isn’t white. It only seems that way because your eyes haven’t adjusted to see the tonal range of objects in front of you. The same is true of the film and the image sensor in the back of your camera.

Film and image sensor tonal range Film and image sensors like those found in digital cameras can only handle a certain tonal range of any subject matter. When we refer to tonal range we mean the range between the brightest and darkest values in a scene. When the tonal value of a subject is higher than the range your film or image sensor can handle, the objects appear white, even though they really aren’t. To compensate for this, you adjust your camera’s exposure. When you do, you don’t widen the tonal range; you only select which part of the object’s range to use.

Exposure adjustment The adjustment you make, however, doesn’t come without a price, although there are ways to work around this. As you adjust your exposure downward to accommodate the shadow areas, as shown in Figures A1 and A2, the highlight areas become lighter and you begin to lose highlight detail. The photo then has an overexposed appearance, as shown in Figure A3.

Figure A: A1

A2

A3

About the Threshold command

If the highlight areas in an overexposed photo don’t seem to contain much detail, then how does the Threshold command help to restore them? In the same way that you can see a much wider tonal range, the tonal range of film or an image sensor is wider than your monitor. There’s usually a certain amount of highlight detail present that your monitor just can’t process. The Threshold command is able to isolate the highlight areas in your photo. Then, after you select, copy, and paste them into a new layer, you can adjust the highlight tonal level to add detail to the highlight areas in your photo.

Correcting for slight overexposure

Let’s correct a slightly overexposed photo. To follow along using our...