For images in which unnatural coloring is more obvious (such as photos that include people), a levels adjustment layer may not be precise enough to adjust the color tint suitably. In such cases, you'll want to use a Curves adjustment layer instead.

First, open the Info palette. Hover the cursor over an area of the image that you know should be gray (or close to gray)—in the example on the next page, I chose the wall area in the background. Note down the RGB values of this area, because we'll need them later. My wall has a red value of 128, a green value of 145, and a blue value of 173. Calculate the average of the three values—in this example, it's about 149.

Noting RGB values of the wall

Next, we'll add the curves adjustment layer. Click on the Create new fill or adjustment layer button at the bottom of the Layers palette, and select Curves, from the menu that appears, as shown at right. The Curves dialog box will be displayed, as shown below.

Adding a point to the Red channel

Adding a curves adjustment layer

In the dialog box, select Red from the Channel dropdown to display the curve (initially a straight line) for the red channel. You can also jump straight to the red channel using Ctrl-1 (Command-1 on a Mac). Click somewhere on the line to add a new point.

Adding a point to the Red channel

In the Input field, type in the red value that you noted earlier. In the Output field, type in the average of the RGB values. As you can see in the example shown on the right, I've typed in my red value of 128, and my average of 149.

Now, repeat the same process for the green and blue channels: click on the line to add a point, enter the original green or blue values in the Input field, and enter the average in the Output field.

Changing the Input and Output values

It's unlikely that the gray pixel we initially chose was "pure" gray. If we follow this process, Photoshop will adjust the curves so that the gray pixel is really gray (with equal red, green, and blue values). It will then adjust the rest of the image accordingly, so that it looks more natural.

The examples below show the original photo, plus two adjusted versions of the photo—the first adjusted using levels, the second using curves.

Comparing adjustment techniques

Comparing adjustment techniques

TIP Jumping Around

Just as you can "jump to" the red channel using Ctrl-1 (Command-1), you can also quickly access the green and blue channels using Ctrl-2 or Ctrl-3 (Command-2 or Command-3), respectively.

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