Apple Color 1.0 - Manual (Page 166)

166 Chapter 9 Primary In
Step 4: Make more specific adjustments
If you still feel that there are specific aspects of the image that need further adjustment
after steps one through three, you can turn to the curves controls, which let you make
targeted adjustments to the color and contrast of the image within specifically defined
zones of tonality. Past a certain point, however, it may also be easier to move on to the
Secondaries room, covered in Chapter 10, “
Secondaries ,” on page 209.
Using the Primary Contrast Controls
If you strip away the color in an image (you can do this by setting the Saturation
control to 0), the grayscale image that remains represents the luma component of the
image, which is the portion of the image that controls the lightness of the image. As
explained in “
The Y’C
B
C
R
Color Model ” on page 24, the luma of an image is derived
from a weighted ratio of the red, green, and blue channels of the image which
corresponds to the eye’s sensitivity to each color.
Although luma was originally a video concept, you can manipulate the luma
component of images using the contrast controls in Color no matter what the
originating format. These controls let you adjust the lightness of an image more or less
independently from its color.
Note: Extreme adjustments to image contrast may have an effect on image saturation.