Operation Manual

Adjusting the Tonal Curve of the Blue Color Channel
You adjust the tonal curve of the blue color channel when you want to remove blue and
yellow color casts in the image.
Before Blue Curves adjustment After Blue Curves adjustment
EffectBlue adjustment
Adds yellow to the shadows, removing blue.Move tonal curve down in the
shadows
Adds blue to the shadows, removing yellow.Move tonal curve up in the
shadows
Adds yellow to the midtones, removing blue.Move tonal curve down in the
midtones
Adds blue to the midtones, removing yellow.Move tonal curve up in the
midtones
Adds yellow to the highlights, removing blue.Move tonal curve down in the
highlights
Adds blue to the highlights, removing yellow.Move tonal curve up in the
highlights
Working with the Levels Controls
You use the Levels adjustment controls when you want to manually set the tonal values
of the shadows, midtones, and highlights in an image. By default, Aperture sets 0 as pure
black and 1 as pure white. Constraining the white and black point values evenly
redistributes the tonal range of the pixels between black and white. Reapportioning the
luminance values increases the tonal range and contrast in the image. However, if you
clip too far into either the black or white tonal values, tonal values that were originally
near pure black and pure white are now changed to pure black and pure white, resulting
in lost image detail.
554 Chapter 17 Making Image Adjustments