Mastering Image Exposure Corrections in Photoshop

Adapted from Digital Photography: Expert Techniques (O'Reilly)
By Ken Milburn

Dateline: June 29, 2005
Version: Photoshop CS

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It's very important to always do your exposure corrections in Photoshop first, before any other corrections or effects. If you don’t, you’ll find that correcting exposure is extremely hard (if not impossible) to do. For example, look at the difference that exposure correction makes between the two images below.

An image after corrected export from the Camera RAW plug-in (top).
The same image after further exposure corrections in Photoshop (bottom).

Here’s how to do exposure corrections in Photoshop. If you’re not using the Adobe Camera RAW support, make sure your camera’s RAW file conversion software saves in 16-bit format. Next, open Photoshop, load your image, and use the following routine.

  1. As soon as you’ve opened a new file in Photoshop, choose Image > Duplicate. In the Duplicate Image dialog, add “-cor” (short for “exposure corrected”) to the filename (see below). Then click OK.

  2. When the duplicate file window appears, select the original file window and click the Close button. You’ll be asked if you want to save the file. Since the purpose of this workflow is to keep the original undisturbed, click No. This is especially true if the image is a JPEG that may deteriorate each time it’s saved due to repeated image compression.

  3. Press Cmd/Ctrl-L (or do it slowly and painfully by choosing Image > Adjustments > Levels). The Levels dialog appears.

    The Levels dialog as properly adjusted for the Red channel.

  4. The first thing you should do is spread the histogram across the visible spectrum of brightness values. If you do this for each color channel independently, you will simultaneously perform a color correction to the image that can be adjusted to suit your preferences with minimum hassle and maximum chances for success. So, press Cmd/Ctrl-1 to first isolate the histogram to the Red channel.

  5. Drag the shadow slider at the left of the histogram (for the Input Levels, not the Output Levels) to the first point that shows pixels in the histogram. Some image’s histograms will show quite a rise at the very end. If there is no empty space at the shadow (black slider) or highlight (white slider) end of the histogram, don’t move the slider for that end. Do not move the midtone (gray) slider for any of the color channels at this time.

  6. Repeat this for the other color channels (i.e., green and blue). When you have adjusted all of the channels according to the instructions in Step 5, press Cmd/ Ctrl-~. You will see the histogram for the composite RGB channel. In the rare case that there is still a gap between the shadow or highlight end of the histogram and the histogram window, adjust the slider for that end of the histogram. See the illustration below.

    The Levels dialog after properly adjusting the composite (RGB) channel.

  7. Now you can adjust the midtone brightness of the image using the gray slider. If you want to force higher contrast in the image, move the highlight and shadow sliders in toward the center until you get the effect you are looking for.

    The Levels dialog after adjusting for brighter midtones.

  8. Lastly, you may need to change the overall color balance using the Levels command, even though your adjustments up to this point have made the color balance “theoretically correct.” Perhaps you shot the image too far off-balance to achieve correct color balance without forcing it. Or you may want to create a certain mood by giving the image a cooler or warmer color-cast. You can do this by doing what I told you not to do before: move the midtone of the primary color(s) that are most likely to shift the color in your preferred direction. Dragging any color channel’s midtone slider to the right will intensify that primary color, while dragging it to the left will intensify its opposite (in the Red channel, dragging the slider to the left will add Cyan; in the Green channel, it will add Magenta). So if you want a cooler (bluer) image, press Cmd/Ctrl-3 to access the histogram for the Blue channel and then drag the midtone slider to the right. If you want a warmer tone, drag the midtone slider to the left. About 85% of the time, you can get the color balance you want by adjusting only one primary; if you don’t, there’s no law to prevent you from tweaking the other two.

    You now have an image with almost perfect exposure correction. But “almost perfect” isn’t quite perfect enough. So there are a couple more things you can do using the Curves and Hue/Saturation commands. First, press Cmd/Ctrl-M to bring up the Curves command.

    The Curves dialog before making any adjustments.

  9. Use the Zoom tool (or enter a Zoom Level in the small box at the left end of the Status bar) to make the image small enough so that you can see the entire image in addition to the Curves dialog.

  10.  Move the cursor over the image (notice that the cursor turns into an eyedropper). Find a specific tone that you want to lighten or darken (perhaps you want to darken the shadow side of a face or brighten the leaves on a tree), and Cmd/Ctrl-click directly over that area. A black dot will appears on the curve line at the point that precisely represents the area you want to brighten.

    Occasionally, you’ll overdo placing and dragging curve points and come up with a surprisingly ugly result. The easy cure is to start over by pressing the Opt/Alt key and clicking the Reset button (before you pressed Opt/Alt it was the Cancel button).

    The circle on the diagonal line shows the exact level of
    brightness under the point of the cursor (eyedropper) in the image.

  11.  Place a point on either side of the dot. This will anchor the curve line so that it doesn’t move when you adjust the area that you highlighted above.

  12.  To brighten the chosen area, drag its dot up; to darken it, drag its dot down. For example, in the illustration below, the dot was dragged down slightly.

    Dragging up the dark dot in the center brightens the shades between
    the dots that were placed on either side. You can manually control specific
    areas of brightness by adding and dragging more dots.

You’re done! Save the file and, if you’re curious, compare the original with the corrected version to see what you’ve done.

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This article is adapted from Digital Photography: Expert Techniques (O'Reilly) by Ken Milburn and is reproduced here with permission. Copyright 2004, O'Reilly.