Apple Aperture 2 - Manual (Page 435)

Chapter 15 Making Image Adjustments 435
III
Adjusting the Levels of the Blue Color Channel
You adjust the levels of the blue color channel when you want to remove blue and
yellow color casts in the image.
Working with the Highlights & Shadows Controls
You use the Highlights & Shadows adjustment controls to correct the exposure in images
shot in complex lighting conditions. For example, you can use the Highlights & Shadows
controls to correct the exposure of the darker areas (shadows) of an image that was
otherwise correctly exposed for silhouette. You can also use the Highlights & Shadows
controls to retrieve detail in extremely bright areas of an image. This is particularly useful
when adjusting images of clouds, snow, or images correctly exposed for the shadow areas.
Using the Highlights & Shadows controls is the best way to optimize your image’s
exposure in the highlights, midtones, or shadows without compromising detail in the
other areas of tonality.
Move Gray Levels slider right Adds magenta to the midtones, removing green.
Move White Levels slider left Adds green to the highlights, removing magenta.
Green adjustments Effect
Blue adjustments Effect
Move Black Levels slider right Adds yellow to the shadows, removing blue.
Move Gray Levels slider left Adds blue to the midtones, removing yellow.
Move Gray Levels slider right Adds yellow to the midtones, removing blue.
Move White Levels slider left Adds blue to the highlights, removing yellow.
Before Blue Levels adjustment After Blue Levels adjustment
(moved White Levels and Gray Levels sliders left)