Operation Manual

To automatically adjust the levels based on an evaluation of each color channel
1 Select an image.
2 In the Levels area of the Adjustments inspector or the Adjustments pane of the Inspector
HUD, choose RGB from the Channel pop-up menu, then click the Auto Levels Separate
button.
Click the Auto Levels Separate
button to automatically set the
levels for the image based on an
evaluation of each color channel’s
luminance values.
The levels of the image are automatically adjusted for each color channel. To fine-tune
the levels adjustment, see Adjusting the Luminance Levels in an Image.
Setting the Auto Levels Options
Aperture provides the option to set both the black and white clipping point parameters
for the Auto Levels adjustments. Modifying the black and white clipping points from their
default value of 0% expands the tonal range of the image. One reason for expanding the
tonal range of an image is to preserve shadow and highlight detail when the image is
printed.
Note: You may have to perform a few print tests to determine the output characteristics
of your printer before settling on final values for black and white clipping points.
To adjust the black clipping point
1 Choose Aperture > Preferences, then click Advanced.
Use the Auto Adjust Black
Clip slider and value slider
to add tolerance to
Auto Levels adjustments
when evaluating colors
beyond black.
557Chapter 17 Making Image Adjustments