HP Designjet Z6200 Photo Printer - Manual (Page 103)

What is color?
We see the world around us as steeped in color. Color is in the first instance simply an aspect of how
we experience our environment and is therefore subjective. Our color experiences are closely related to
brain activity that is triggered by signals that our eyes send to it. These signals undergo a complex and
highly interlinked sequence of processing stages that make the relationship between what our eyes emit
and what we experience anything but direct. The signals sent by the eye depend on the light-sensitive
cells that line the back of our eyes, and they belong to three types, each sensitive to electromagnetic
radiation of different physical properties (wavelengths). Such electromagnetic radiation is called light
and objects appear to have certain colors because of how the objects interact with light (by emission,
reflection, absorption, transmission, scattering, etc.).
Our individual experiences of color are also affected by our previous experiences and memories and
by the way in which we put our experiences into language. Finally, environmental factors such as
changes in lighting, scene content, or the proximity of other colors also have an effect, which makes the
way in which we view a given display or print an essential part of the colors we see. Differences in all
these aspects (from physiological differences between people, to differences in their past experiences,
memories and linguistic tendencies) can result in people talking about colors differently even in
response to the same light reflected from an single object. However, many similarities exist between
how individuals experience color. You can make very specific judgments about color that others will
also agree with when care is taken in the process. In conclusion we can say that color results from the
interaction between light, objects, and a viewer, which makes it a very complex and to a large degree
subjective phenomenon.
The problem: color in the computer world
Color-imaging devices such as printers, displays, projectors, and televisions create colors by using
different methods and materials (colorants). Displays, for instance, use colorants that emit red (long
wavelength), green (medium wavelength), and blue (short wavelength) light. A white color requires all
three colorants and black requires that none of them be used (i.e. that no light be emitted). Devices that
use light-emitting colorants are called additive, because the light from them is added together before it
enters a viewer’s eyes. Printers, on the other hand, use materials that absorb parts of the light that
shines on them. They are called subtractive. Typical prints use cyan (red absorbing), magenta (green
absorbing), and yellow (blue absorbing) inks and an additional black ink that absorbs light at all
wavelengths. To get white using a printer requires not absorbing any of the light that illuminates a
piece of paper and to get black, all of the inks need to be used to absorb all of the light that is present.
ENWW What is color? 95
Color management