Apple Aperture 3.5 - Manual (Page 296)

Chapter 7 Make image adjustments 296
There are two ways to perform an automatic levels adjustment. When you want to correct an
image’s contrast without modifying its color cast, you use the Auto Levels Combined button to
adjust levels based on the total luminance of the combined red, green, and blue color channels.
Before Auto Levels Combined adjustment After Auto Levels Combined adjustment
When you want to correct the image’s color cast in addition to its contrast, you use the Auto
Levels Separate button to adjust levels based on an evaluation of each channel.
Before Auto Levels Separate
adjustment
After Auto Levels Separate
adjustment
You can also adjust the tolerance of the black and white clipping points of the Auto
Levels adjustment.
In addition to adjusting the tonal values of an image for overall shadows, midtones, and
highlights, you can color correct an image by adjusting the levels of the red, green, and blue
channels independently. Aperture provides a way to adjust levels for each color channel,
allowing you to control the color tonality in an image.
You can also brush the Levels adjustment on specific areas of an image. For more information,
see
Apply brushed adjustments on page 228.
Adjust the levels of an image automatically
1 Select a photo.
2 In the Adjustments inspector or the Adjustments pane of the Inspector HUD, choose Levels from
the Add Adjustment pop-up menu.
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