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89
Adobe Photoshop Help
Working with Color
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89
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 compo-
nents: the
a
component (from green to red) and the
b
component (from blue to yellow).
L*a*b* model:
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. In the color picker, the
a
component (green-
red axis) and the
b
component (blue-yellow axis) can range from +128 to –128. In the
Color palette, the
a
component and the
b
component 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 2 and 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. (See
“Specifying 8-bit color display (Photoshop)” on page 91
.)
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.
B
C
A
D
