Apple Aperture 2 - Manual (Page 436)

436 Part III Performing Image Adjustments
Adjusting Brightness Values in the Highlight Areas
of the Image
When you want to adjust the brightness values in the highlight areas of the image
without affecting the midtones and shadows, you can adjust the Highlights parameter.
Although the human eye is more sensitive to details in shadow areas than in highlight
areas, such as snow, there is usually a fair amount of visual information that you can
retrieve in the highlights using the Highlights parameter controls. Another example of
when to use the Highlights controls is when the background of your image is correctly
exposed, and the foreground of the image is slightly overexposed. In this case, you use
the Highlights controls to make the overexposed foreground match the exposure of
the correctly exposed background.
Before Highlights adjustment After Highlights adjustment