Apple Aperture 2 - Manual (Page 369)

Chapter 15 Making Image Adjustments 369
III
Using the Auto Levels Combined Button
When you want to quickly adjust the levels of an image based on total luminance
values—red, green, and blue channels combined—you use the Auto Levels Combined
button. Red, green, and blue channels are adjusted by the same amount based on the
total luminance. You use the Auto Levels Combined button when you want to correct
the contrast of the image without modifying the color cast of the image.
To automatically adjust the levels of an image based on total luminance:
1 Select an image.
2 In either the Adjustments inspector or the Adjustments pane of the Inspector HUD, click
the Auto Levels Combined button.
The levels of the image are automatically adjusted. To fine-tune the levels adjustment,
see “
Working with the Levels Controls ” on page 429.
Before Auto Levels Combined adjustment After Auto Levels Combined adjustment
Click the Auto Levels
Combined button to
automatically set the
levels for the image
based on the combined
luminance of all three
color channels.
The luminance
histogram is displayed
as a gray graph.