Before understanding color models, it is essential
to understand different systems. Many of us are aware of the colors
as paints. Hence when we mix blue and yellow, we get the shade of
green. But the result will be different if we mix green and red
light. It will create yellow if 100% red and green light are mixed.
So let us understand these two different properties. If we consider
the colors produced by the monitor, the light beams generate it.
It is based on the RGB model and it is additive color model. Then
comes to paint or printing inks. This is based on CMYK model, which
is subtractive color model.
Computer creates the colors based on RGB model. It
produces spectrum of visible light. Monitor can create millions
of colors by combining different percentages of three primaries,
red, green and blue. While using the image processing software like
Photoshop you can see that these RGB colors are added with the help
of numerical value, which is between 0 to 255. With RGB, mixing
of red and green equally gives yellow, mixing of green and blue
creates cyan and the mixing of red and blue creates magenta. When
all the three colors, red, green and blue are mixed equally they
produces white light. Hence it is called Additive color model. Another
RGB model based example is human eye itself and scanners.
The basic advantage of RGB model is; it is useful
for full color editing because it has wide range of colors. But
at the same time this model is said to device dependent. It means
the way colors displayed on the screen depends on the hardware used
to display it.
Opposite model of RGB is CMY. Printing inks are based
on this model. With the full presence of cyan, magenta and yellow
we get black. But practically in the printing industry it is impossible
to create black with these three colors. The result of the mixture
of CMY is muddy brown due to the impurities of the printing inks.
Hence black ink is added to get solid black. The outcome of this
process CMYK model and k stand for black color, which is also recognized
as 'key' color. Since black is a full presence of color, you will
have to subtract the levels of cyan, magenta and yellow to produce
the lighter colors. This can be explained in different way. When
light falls on the green surface or green ink. It absorbs (subtracts)
all the colors from light except green. Hence the model is called
subtractive model. Print production is based on this model.
It is useful to have proper understanding of the color models. The
monitors as well as scanner works on RGB principle. While scanning
we can adjust the software to produce desired result. CMYK is for
print industry. It cannot produce the color range of RGB hence after
finishing the work on computer in RGB mode when you convert it into
CMYK for printing some tonal changes can be occurred. In spite of
its limitation CMYK model is considered as best model available
for printing because it can produce properly finished output.