have been theorizing and developing color models for years in the
hope of coming up with an ideal way to describe color. These color
models are nothing more
than mathematical formulas for describing color. Modern day computers,
operating systems and applications like Adobe Photoshop have no
problem interpreting and converting from one color model to another.
How do we quantify the visual aspects of color numerically or on
There are a
number of different color models that describe and quantify color
for us. There are device dependent color spaces like RGB
(red, green, blue), which is the color model utilized by
the monitor you are viewing this from and CMYK (cyan, magenta,
yellow and black) the model used for ink on paper or other
materials. Another model quite popular with graphics and imaging
software applications is HSB (hue, saturation and brightness).
We will take a look at all three of these color models and also
one device independent color model CIELAB.
transmits, displays or captures light utilizes the RGB color model.
Computers, scanners, televisions, digital cameras and human vision
are all based on this color model. The three primary colors, red,
green and blue constitute the RGB additive color model. As you add
light the color becomes brighter, add red, green and blue light
together in equal proportions and you will get white light. Different
combinations of red, green and blue produce a myriad of different
colors. If you work with 8 bit images in Adobe Photoshop you will
have access to approximately 16.7 million colors and billions of
colors at higher bit depths.
The CMYK color
model is based on ink on paper. These inks absorb and reflect different
wavelengths of light. Cyan absorbs all red light, magenta absorbs
all green light and yellow absorbs all blue light. If these three
inks absorb all red, green and blue light then in theory the combination
of all three on paper should produce black, in reality however there
are no completely pure inks and as such not all of the red, green
and blue light will be absorbed. The printing industry compensates
for this problem by adding a fourth ink, black to the process. The
addition of black allows us to produce good blacks on press and
other output devices like inkjet printers.
The CMYK color
model is called the subtractive color model because as additional
inks are added color is subtracted, opposite of the RGB additive
color model. Please note that RGB and CMY colors are opposite or
complimentary colors. See the diagrams above and below.
model is based on Hue, Saturation and Brightness (or lightness).
Hue is basically your color control; a hue can be red, orange, purple,
green, etc. Saturation is the variable for the intensity or saturation
of the color; how vivid a red or purple do you want? Brightness
quite obviously controls the brightness or lightness of your color.
The HSB model is still used extensively in image editing applications
like Photoshop, in graphic design and is still popular with interior
decorators for paint selection and categorization.
Last but not
least is the CIELAB color model. Created in 1976 this is a refined
color model based on the original CIE XYZ model developed in 1931
by the International Committee on Illumination or la Commission
Internationale de l' Eclairage, the French translation.
CIELAB is based
on a three dimensional model of color that includes the three primaries,
L*, a* and b* (pronounced, L star, a star and b star).
As you look
at this diagram, a* represents how green or red the color is, b*
how yellow or blue and L* lightness. Although it may not be very
intuitive to work with CIELAB it is a highly accurate mathematical
model that emulates normal human color vision based on standard
viewing conditions, light sources and a defined "standard observer"
set by the CIE. This color model includes all of the colors visible
to the human eye.
previous color models mentioned here, CIELAB, because it is based
on human vision and set standards is device independent. It is utilized
in the color management workflow as a universal translator that
enables us to move between color spaces without bias. For example
if we started out with a digitally captured image in RGB mode we
could use CIELAB and a conversion engine like Colorsync to convert
the original RGB color values to CMYK for output to a printer with
minimal change to the original color values.
CIELAB is a
key component of the color managed workflow and without it managed
color between devices would be extremely difficult if not impossible.
You will most likely utilize all of the color models discussed here,
get to know them all and the flow of color through your workflow
will be easier to understand and manage.
Ok, let's move
on to the next step... putting this all to together into a managed
ICC color workflow.
Concepts and terminology....
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Color Model is simply a mathematical formula for describing
Color Model: Add Red, Green and Blue colors together to
create white light, known as an additive color model. Example:
Color Model: Cyan, magenta, yellow and black, ink or dye
on paper. Add ink/dye and color is subtracted, known as
subtractive color model. Example: Inkjet print.
Color Model: Control Hue, Saturation and Brightness. Used
in many editing and scanning applications.
Color Model: Emulates normal human color vision and unlike
the other color models noted here is device independent.
Used as a universal color translater, integral component
of ICC color managed workflow.