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Click OK to accept the changes. 24 The gray card (to the right) can help balance color at three levels of gray. 25 Each of the curves should look almost exactly like the curves pictured here for red, green, and blue when you make the corrections. Red Green Blue When you are done correcting the color, you can use the measurements to correct tone as well. Because you know that the card is 25, 50, and 75 percent gray (191, 128, and 63 levels), the measurements you checked will correspond to those values.

Open the Channels palette if it is not already visible. Do this by selecting Window ➔ Channels. 3. Choose Merge Channels from the Channels palette. 3. 4. Choosing Merge Channels opens the Merge Channels dialog box. Choose RGB from the Mode dropdown menu, as shown here. Be sure the number in the Channels field is 3, and click OK. The Merge RGB Channels dialog box will open. 5. psd as Blue, as shown here, and then click OK. These five steps will create a color image from the three black-and-white images you opened in step 1.

For more complicated shifts, this type of correction may need to be used in conjunction with a curve (or other) correction to better control the result. psd. You can compare the before and after by clicking Open on the History palette and then clicking the final step. Using the Levels tool in this way is based on solid science and works as a general correction technique for almost any image. The reason has to do with visible light and the way we perceive light. A scene will usually appear to your eye to have a full dynamic range in tone from white and black.