Apple Aperture 2 - Manual (Page 363)

Chapter 14 An Overview of Image Adjustments 363
III
Using Histograms to Correct Images
A histogram can also be used as a tool to evaluate whether or not there is enough
shadow, midtone, and highlight information in the image. Aperture provides two
histograms in the Adjustments inspector and the Adjustments pane of the Inspector
HUD. The histogram above the adjustment controls indicates the current state of the
image. The Levels histogram included with the Levels adjustment controls provides a
way to adjust the brightness values in the image in relation to the displayed histogram.
You use the Levels controls to adjust the shadow, dark quarter-tone, midtone, light
quarter-tone, and highlight values independently of each other without affecting the
other areas of the image. For more information about performing levels adjustments,
see “
Working with the Levels Controls ” on page 429.
About Making Adjustments Onscreen
Human eyes perceive color subjectively. It’s difficult for the human eye to make
objective changes to the colors in an image because the brain is so advanced that it
skews the perception of colors to make them appear as natural as possible. For this
reason, it is essential that you create the best possible work environment for
performing color adjustments. Such an environment excludes extraneous colors that
have the potential to throw off your eye.
Creating a Good Work Environment
Before you begin making color adjustments to your images, it’s important to pay
attention to the following:
 Set your display to its highest-resolution setting. This will give you the best view of
your image.
 Make sure you are employing good color management. This means that your
displays and printers are calibrated and their profiles are up to date. For more
information about calibrating and profiling your Aperture system, see Appendix B,
“
Calibrating Your Aperture System ,” on page 635.
 Reduce the ambient light in the room you are working in to prevent the light from
skewing your perception of the colors on your screens, and make sure your displays
are set to their brightest levels.
 If possible, paint the walls in the room in which you perform detailed image
adjustments a neutral gray. Keep bright-colored objects to a minimum to ensure
that the colors on your screens are not altered by the color in the rest of the room.