3.3

Chapter 17 Making Image Adjustments 364
3 If you want to adjust the Highlights & Shadows advanced settings, click the Advanced disclosure
triangle to show the advanced Highlights & Shadows controls, then do the any of the following:
Click the disclosure triangle to
reveal the advanced Highlights
& Shadows controls.
•
To set the area Aperture uses to determine each pixel’s tonality: Use the Radius parameter controls.
•
To set the amount of saturation applied during a Highlights or Shadows adjustment: Use the Color
Correction parameter controls.
•
To set the range of tones that are modied in the highlights: Use the High Tonal Width
parameter controls.
•
To set the amount of contrast in the midtones: Use the Mid Contrast parameter controls.
•
To set the range of tones that are modied in the shadows: Use the Low Tonal Width
parameter controls.
Working with the Levels Controls
An Overview of the Levels Adjustment
You use the Levels adjustment controls when you want to manually set the tonal values of the
shadows, midtones, and highlights in an image. By default, Aperture sets 0 as pure black and 1
as pure white. Constraining the white and black point values evenly redistributes the tonal range
of the pixels between black and white. Reapportioning the luminance values increases the tonal
range and contrast in the image. However, if you clip too far into either the black or white tonal
values, tonal values that were originally near pure black and pure white are now changed to pure
black and pure white, resulting in lost image detail.
To simply your workow, you can use the Auto Levels buttons in the Levels adjustment to
analyze the image and adjust the levels based on that analysis. This is a good way to make
a quick correction to an image before ne-tuning the Levels adjustment with the manual
adjustment controls.
There are two ways to perform an Auto Levels adjustment. For more information, see the
following sections:
•
Automatically Adjusting Luminance on page 365
•
Automatically Adjusting RGB Channels on page 366
You can also adjust the tolerance of the white and black clipping points of the Auto Levels
adjustment. For more information, see Setting the Auto Levels Options on page 366.
In addition to adjusting the tonal values of an image for overall shadows, midtones, and
highlights, you can also 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.