Computers store color information as numeric codes. Because of the
various needs of graphic artists, web designers, publishers, photographers, etc.
different sets of codes have been created to serve their particular needs.
These different sets of codes are known as color spaces. A color space is
intended to reproduce a certain range of colors. The range of colors in a
color space is called its color gamut.
Figure 1. There are two color spaces above, A and B. Color
Space A has a 24 color, color gamut. Color space B has a 12 color,
Color space is a predefined set of visible colors. Specifically, a
given set of numeric codes used to reproduce a specific color gamut is called a
color space. Some of the color spaces you may have heard of are sRGB,
Adobe RGB (1998), Lab, etc.
A good analogy can be seen in Figure 1. Figure 1 shows two sets of colored
pencils. The set on the left has 24 different color pencils. The set
on the right has 12. We can consider these two packs of pencils as
representing two different color spaces because they have a different set of
Color gamut is the specific range of colors in a color space. Using
Figure 1 again, the 24 pencil color space can produce twice as many colors as
the 12 pencil color space. Therefore, the 24 pencil color space has a
wider color gamut than the 12 pencil color space.
Color models are a way to categorize color spaces. For example, sRGB
and Adobe RGB (1998) are two different color spaces that have different color
gamuts but they belong to the same RGB color model. CMYK is another color
model as well as Grayscale and Lab. An image's color model is referred to
as its color mode.
There are two kinds of color profiles: image profiles and device profiles.
An image profile tells the hardware and software what color space the image is
in. Device profiles use this information to reproduce the colors.
Device profiles are separate computer files that tell the hardware and software
how to reproduce color. Image profiles are part of the image file and tell
all devices the numeric code set to use when interpreting and reproducing an
image's colors. Image profiles define color. Device profiles
In digital photography, there are many devices involved in the storage and
reproduction of color. For example, digital cameras, scanners, computers,
monitors and printers. When a monitor is calibrated, a device profile is created
and stored on your computer. Your hardware and software use the monitor's
profile to reproduce colors on the monitor. Device profiles are commonly
called by the hardware they are associated with. For example, a printer
profile or a monitor profile or a scanner profile. But they are all device
profiles. The device profile takes the numeric codes in the image and
translates them into color based on the image's color profile. Device
profiles are not associated with any single image.
When digitally capturing an image or when editing it, we can tag an image
with an image profile. Tagging means denoting in the image file's properties what
color space should be used to interpret the numeric codes. This color
space information is referred to as an embedded profile and these profiles are
not separate files. Embedded profiles tell the hardware and software what
color space is associated with an image.
There are a wide variety of color spaces. Only the common ones used in
digital photography are discussed here.
||Number of Channels
Web, monitor and projector display. Even
though it is impossible to create an image that will look identical on
all monitors and web browsers, the sRGB color space is supported by the
web environment more than most other color spaces.
Total color gamut is smaller than Adobe RGB (1998). While there
are colors in sRGB that are not part of Adobe RGB (1998) and vice versa,
in total, the Adobe RGB color space contains more colors than sRGB.
|Adobe RGB (1998)
Commonly used in
workflows intended for photo inkjet printers. Has one of the
larger color gamuts of the RGB color model. A well supported color space.
Has a wider color gamut than Adobe RGB.
However, it is not as widely supported as Adobe RGB or sRGB.
Interestingly, it can contain colors not visible to the unaided human
Commercial process color printing. Smaller
color gamut than RGB. Not intended for master files.
Intended for output files to be printed on large scale commercial
printers. A master file is most often in a RGB color
model. If needed, a copy is then made, converted to CMYK, and the
CMYK copy is given to the print shop.
Only color space that Photoshop allows to be
used with their duotone, tritone and quadtone features.
Device independent color space. The color
gamut is the entire visible spectrum. Stores luminance on a
separate channel from the hue and saturation information. Green
and red information are stored on the a channel. Blue and yellow
information are stored on the b channel. Hence the name, Lab.
The only color mode (in Photoshop) that separates color from lightness,
Often used by color space conversion routines as an intermittent step.
For example, when converting a RGB image to CMYK (and vice versa),
Photoshop first converts the image to Lab and then converts it to the
destination color space.
Table 1. Color Space Comparison
Raw is not a color space, it is a file format. You
can read about the Raw format on the
File Format page.
One of the quickest ways to become frustrated in digital photography is not
to use a good color managed workflow. For example, assume we capture an
image in the sRGB color space. Then in Photoshop we assign the Adobe RGB
(1998) profile to it. What we just did was tell all devices that will
process that image, including Photoshop, to interpret the sRGB numeric codes
using the Adobe RGB (1998) code set. Since the numeric codes for sRGB are
not the same as the codes for Adobe RGB (1998), then the incorrect colors will
be reproduced. If an image's color space needs to be changed, the color
space has to be converted from the existing color space to the desired color
Converting an image from one color space to another is easy. In
Photoshop, click Edit > Convert to Profile. Select the desired
destination space and click OK. Save the image so the new profile is
Be sure you select Convert to Profile and not Assign Profile. Convert to
Profile is not the same as Assign Profile. Converting takes the numeric
codes in the existing color space and converts them to the numeric codes of the
desired color space. Assign Profile does not convert the numeric codes.
It tells the software to interpret the existing numeric codes using the newly
assigned profile. And if the numeric codes are not for the assigned
profile, then colors will be incorrectly reproduced.
Be sure to read the
Photoshop Color Settings page to learn about setting up Photoshop to work
with profiles and color spaces.