Apple Aperture 3.5 - Manual (Page 287)

Chapter 7 Make image adjustments 287
Use eyedropper tools to set black, gray, and white points
You use the Black Point, Gray Point, and White Point eyedropper tools in the Curves adjustment
controls when you want to have Aperture selectively modify the tonal values of the shadows,
midtones, and highlights in an image automatically. Using an eyedropper tool, you sample the
pixels of the tonal value in the image you intend to correct, and Aperture places a point on the
tonal curve and automatically adjusts the image so that the pixels that fall in the same tonal
range as the sampled pixels are set to either black, gray, or white. For example, you use the Black
Point eyedropper tool to select the specific area of the image that should be black. Aperture
samples the pixels within the selection, places a point on the curve, and then adjusts the curve
to make the selected pixels—and all other pixels in the image of the same tonal value or
darker—black.
Before Black Point Curves adjustment After Black Point Curves adjustment
Before Gray Point Curves adjustment After Gray Point Curves adjustment
Before White Point Curves adjustment After White Point Curves adjustment
67% resize factor