- Why
colors don't match -- No device in a
publishing system is capable of
reproducing the full range of colors
viewable to the human eye. Each device
operates within a specific color space,
which can produce a certain range, or
gamut, of colors.
The RGB (red, green, blue) and CMYK
(cyan, magenta, yellow, black) color
modes represent two main categories of
color spaces. The gamuts of the RGB and
CMYK spaces are very different; while
the RGB gamut is generally larger (that
is, capable of representing more colors)
than CMYK, some CMYK colors still fall
outside the RGB gamut. (See Color gamuts
(Photoshop) for an illustration.) In
addition, different devices produce
slightly different gamuts within the
same color mode. For example, a variety
of RGB spaces can exist among scanners
and monitors, and a variety of CMYK
spaces can exist among printing presses.
Because of these varying color spaces,
colors can shift in appearance as you
transfer documents between different
devices. Color variations can result
from different image sources (scanners
and software produce art using different
color spaces), differences in the way
software applications define color,
differences in print media (newsprint
paper reproduces a smaller gamut than
magazine-quality paper), and other
natural variations, such as
manufacturing differences in monitors or
monitor age.
Color
numbers
Each pixel in an image document has a set of
color numbers that describe the pixel's
location in a particular color mode--for
example, red, green, and blue values for the
RGB mode. However, the actual appearance of
the pixel may vary when output or displayed
on different devices, because each device
has a particular way of translating the raw
numbers into visual color. (See Why colors
sometimes don't match.) When you apply color
and tonal adjustments or convert a document
to a different color space, you are changing
the document's color numbers.
Color
profiles
An ICC workflow uses color profiles to
determine how color numbers in a document
translate to actual color appearances. A
profile systematically describes how color
numbers map to a particular color space,
usually that of a device such as a scanner,
printer, or monitor. By associating, or
tagging, a document with a color profile,
you provide a definition of actual color
appearances in the document; changing the
associated profile changes the color
appearances. (For information on displaying
the current profile name in the status bar,
see Displaying file and image information.)
Documents without associated profiles are
known as untagged and contain only raw color
numbers. When working with untagged
documents, Photoshop uses the current
working space profile to display and edit
colors.
Viewing color around you.
View your documents in an environment that
provides a consistent light level and color
temperature. For example, the color
characteristics of sunlight change
throughout the day and alter the way colors
appear on your screen.
SOURCE:
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