Apple Aperture 2 - Manual (Page 446)

446 Part III Performing Image Adjustments
About Hue, Saturation, and Luminance
Hue (H) describes the actual color itself. Hue is measured as an angle on a color
wheel. Moving a Hue slider in Aperture remaps the color from its original position on
the color wheel to the new position indicated by the slider. Hue adjustments are
often made to match the color of the same subject in different images. Adjusting the
hue of an image is particularly useful when the subject you shot moved between
various lighting conditions. Another advantage of adjusting the hue of an image is
that camera models of different types or from different manufacturers rarely capture
and render color exactly the same way. You can use the Hue controls to match the
color of a subject shot by two different cameras, so that when the images are placed
side by side, they match.
Saturation (S) defines the intensity of a specific hue. A saturated hue gives the color a
vivid and pure appearance. A less saturated hue appears flatter and more gray. A
completely desaturated hue becomes a shade of gray.
Luminance (L) describes the brightness of the selected color. An increase in luminance
brightens the selected color value. A maximum Luminance adjustment results in pure
white. Conversely, a decrease in luminance darkens the selected color. A minimum
Luminance adjustment results in pure black.
L
S H