These three commands — Auto Levels, Auto Contrast, and Auto Color — automatically enhance an image’s color and contrast using light and dark pixels. These commands work quite well with a minimum of fuss. If you find an image needs a little help, these three commands may be all you’ll ever need.
Auto Levels automatically enhances highlights and shadows by replacing the darkest pixels with black pixels and lightest pixels with white pixels. Auto Levels then redistributes the other pixel values in the image proportionately, making an image appear brighter and less murky.
To see an example of the difference Auto Levels can make, take a look at Color Plate 9-5. The image at the bottom right shows Auto Levels applied to an image that is rather dark and murky looking, making it brighter and more vibrant.
To apply Auto Levels to a layer or selected area:
Use the Layers palette to select a layer or the Background.
Figure 9-1 shows an image before the Auto Levels command is applied.
Figure 9-1: This scanned image has a gray cast that needs correcting.
If you want to apply Auto Levels to only part of a layer, use the selection tool of your choice to select an area of the image.
For directions on how to use the selection tools, turn to Chapter 7.
Choose Image→Adjustments→Auto Levels.
Figure 9-2 shows the image from Figure 9-1 after Auto Levels have been applied.
Figure 9-2: After applying Auto Levels, the high-lights and shadows really stand out.
Auto Contrast automatically adjusts the contrast by replacing the darkest pixels with black pixels and lightest pixels in the image with white ones. As a result, shadows appear darker and highlights are lighter. Unlike Auto Levels, Auto Contrast does not change the way other colors look, it only affects the overall contrast of an image.
To apply Auto Contrast to a layer or selected area:
Use the Layers palette to select a layer or the Background.
If you want to use Auto Contrast on only part of the layer, use the selection tool of your choice to select an area of the image.
Choose Image→Adjustments→Auto Contrast.
Figure 9-3 shows the image from Figure 9-1 after Auto Contrast has been applied.
Figure 9-3: After applying Auto Contrast to the image, the lights and darks are much more pronounced.
Auto Color adjusts the shadows, midtones (the middle range of colors in an image), and highlights of an image. Auto Color samples the image and evens out the midtone colors while enhancing the light and dark areas.
Any bright image that appears overexposed (where the colors look washed out) would benefit from the Auto Color command. Darks are enhanced, the extra brightness is toned down, and colors become clearer and more saturated.
To apply Auto Color to a layer or selected area:
Use the Layers palette to select a layer or the Background.
Use the selection tool of your choice to select part of the image or layer if you don’t want to use Auto Color on the whole image.
For directions on how to use the selection tools, turn to Chapter 7.
Choose Image→Adjustments→Auto Color.
Figure 9-4 shows the image from Figure 9-1 after Auto Contrast has been applied.
Figure 9-4: When Auto Color is applied, the entire image becomes brighter and colors are more saturated.