Understanding color on the computer can be a
bit tricky since the computer makes use of more than one type
of color model. This article will address two types of color
spaces - additive and subtractive and explain how they interact
and function.
Additive colors are the colors that are inherent
in light. They are the colors indigenous to monitors, digital
cameras, and scanners. The human eyes, also, sees these colors.
They are red, green, and blue (RGB). They are called primary
additive colors because when added together, they form white.
Subtractive colors are those used in the printing
trades such as dyes, inks, and pigments. I am sure the term
four color separation is familiar to many people. These colors
are cyan, magenta, and yellow. These colors are called absorbing
or subtractive colors since when light is absorbed by all
of them, they produce black. These are the colors used in
printers. They are commonly referred to as CMY colors. However,
usually one sees CMYK. K stands for a truer black since when
100% of C, M, and Y are combined, the resulting color is a
muddy dark brown. All of these colors are related. For example:
white = red + green + blue black = cyan + magenta + yellow
cyan = green + blue red = yellow + magenta
magenta = blue + red green = yellow + cyan
yellow = red + green blue = cyan + magenta
I hope that the above lists show an emerging
pattern - one of interrelationships. RGB and CMY colors
form a complementary relationship.
Red.........Cyan
Green......Magenta
Blue........Yellow
Thus, if I have an image that contains
yellow and I want to intensify the yellow, I can add more
yellow or I can subtract blue. The best way to understand
complementary colors is to set up an image and manipulate
the individual colors.
Computers are capable of generating images of
varying numbers of colors. These can range from 16 colors
to 16 million colors. If an image is created with only 16
colors and this image is turned into a grayscale image, there
are only a certain number of shades of gray possible. Likewise,
if an image that has 16 million colors is turned into a grayscale
image, there are many more shades of gray even though the
human eye cannot discern them all. How can the computer vary
the number of colors or shades of gray? The computer monitor
is made up of red, green, and blue phosphors or light producing
elements. Each of the colors associated with a pixel (picture
element) can have attributed to it a certain number of colors.
Bit-depth determines how many colors or levels of gray each
pixel carries. In scanning for example, a bit-depth of 24
means that the red, green, and blue sources of light each
have 8 bits of color assigned to them. The more color bits
assigned to a pixel, the more colors can be displayed and,
theoretically, the more shades of gray. However, the human
eye can only see a certain number of shades of gray. Also,
not all visual colors can be transmitted to the printed medium.
Thus, for example, when a scanner advertises that it can produce
a bit-depth of 36, this bit-depth will not necessarily produce
a better image than one with a bit-depth of 30 or even 24.
There are other models for assigning colors
to an image:
HSB = Hue, Saturation, & Brightness
HSL=Hue Saturation, & Lightness
HSV=Hue, Saturation, & Value Color Space
Hue = The color of something
Saturation = The strength of a color
Value = How dark or light is a color
The last term to be discussed is that of monitor
gamma. Monitor gamma is basically the numerical representation
of amonitor's contrast
and brightness level. 2.2 is the gamma of Windows monitors. An
image on a monitor set for a gamma of 1.8 appears lighter than
an image on a monitor with a gamma of 2.2.
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