Page 72 - Enhancing CAD Drawings with Photoshop

4386.book Page 55 Monday, November 15, 2004 3:27 PM
MODES AND GAMUTS 55

Figure 2.1
The lagoon image with
the gamut warning
turned on. Some pixels
in the sky are out of
gamut—red on screen
but black here.

6. Click the Lightness channel. This channel carries the grayscale detail in the image, so it should
look like a desaturated version of the image.
7. Click channel a, shown on the left in Figure 2.2. The a channel carries the green-to-red color
component in Lab mode. This channel appears mostly gray with very little contrast.

Figure 2.2
The Lab color “a” channel
(left) and “b” channel
(right) each carry a
portion of the image’s
color information.

8. Click channel b, which carries the blue-to-yellow component. By itself, channel b isn’t much
use. Channels a and b together carry all the color information in the image.

9. Click the Lab composite channel to turn on all three channels at once.
10. Choose Image Mode CMYK. Photoshop mixes the colors that were out of gamut from Lab
to CMYK when you change color modes.
11. Make sure Gamut Warning is checked in the View menu again, and see the change in the
image. No red pixels are shown in the image this time; all the pixels now fit within the CMYK
gamut.