Adobe PHOTOSHOP 6.0 Manual page 122

CHAPTER 3
112
Working with Color
Although CMYK is a standard color model,
the exact range of colors represented can vary,
depending on the press and printing conditions.
Photoshop's CMYK mode varies according to the
working space setting that you have specified in
the Color Settings dialog box. (See "About
working spaces" on page 125.)
L*a*b model
The L*a*b color model is based on the model
proposed by the Commission Internationale
d'Eclairage (CIE) in 1931 as an international
standard for color measurement. In 1976,
this model was refined and named CIE L*a*b.
L*a*b color is designed to be device independent,
creating consistent color regardless of the device
(such as a monitor, printer, computer, or scanner)
used to create or output the image.
L*a*b color consists of a luminance or lightness
component (L) and two chromatic components:
the a component (from green to red) and the
b component (from blue to yellow).
A
B
C
D
A. Luminance=100 (white)
B. Green to red component
C. Blue to yellow component
D. Luminance=0 (black)
Lab mode
In Photoshop, Lab mode (the asterisks are
dropped from the name) has a lightness
component (L) that can range from 0 to 100.
The a component (green-red axis) and the b
component (blue-yellow axis) can range from
+120 to –120.
You can use Lab mode to work with Photo CD
images, edit the luminance and the color values in
an image independently, move images between
systems, and print to PostScript
Level 3 printers. To print Lab images to other color
PostScript devices, convert to CMYK first.
Lab color is the intermediate color model
Photoshop uses when converting from one color
mode to another.
Bitmap mode
This mode uses one of two color values (black or
white) to represent the pixels in an image. Images
in Bitmap mode are called bitmapped 1-bit images
because they have a bit depth of 1.
For more information, see "Specifying 8-bit
color display (Photoshop)" in online Help.
Grayscale mode
This mode uses up to 256 shades of gray. Every
pixel of a grayscale image has a brightness value
ranging from 0 (black) to 255 (white). Grayscale
values can also be measured as percentages of
black ink coverage (0% is equal to white, 100% to
black). Images produced using black-and-white or
grayscale scanners typically are displayed in
Grayscale mode.
Level 2 and
®