Operation Manual

• By default, the Low Tonal Width value slider is set to 40.0. Double-click the number in
the Low Tonal Width value slider, then enter a value from 0.0 to 100.0 and press Return.
Aperture uses the new Low Tonal Width setting to determine the range of shadow tonal
values that are taken into account during a Shadows adjustment. The tonal range begins
at pure black, and increasing the Low Tonal Width parameter value broadens the tonal
range to include tonal values closer to the midtones.
Working with the Curves Controls
You use the Curves adjustment controls when you want to manually set the tonal values
of the shadows, midtones, and highlights in an image using a tonal curve. Unlike the
Levels adjustment controls, the Curves controls do not reapportion the luminance values
in the image by constraining the white and black points. Instead, you use the Curves
controls to precisely remap the position of the midtones relative to the white and black
points. Because the human eye’s perception of light is logarithmic rather than incremental,
a curve is necessary to distribute the luminance values across all tonal ranges in an image
in a way that matches how the eye perceives light in nature.
In addition to adjusting the tonal values of an image for overall luminance, you can also
color correct an image by applying the Curves adjustment to the red, green, and blue
channels independently. Applying a Curves adjustment to each color channel allows you
to control the color tonality in an image.
You can also have Aperture automatically identify tonal ranges in an image using the
Black Point, Gray Point, and White Point eyedropper tools in the Curves adjustment
controls. When you select a tonal range using one of the eyedropper tools, Aperture plots
the corresponding curve over the Curves histogram.
You can also brush the Curves adjustment on selected parts of an image. For more
information, see Making Brushed Adjustments.
Important: The Curves adjustment controls are only available for images using Aperture 3
image processing. For more information about reprocessing your images, see Reprocessing
Images from Previous Versions of Aperture.
538 Chapter 17 Making Image Adjustments