HP Designjet Z3100 Photo Printer series - Manual (Page 72)

What is color?
We see the world around us as steeped in color, where color is in the first instance simply an aspect of
how we experience our environment. Color is therefore subjective. Upon further inspection we find that
our color experiences are closely related to brain activity that is triggered by signals sent to it by our eyes.
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 they
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 will 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. Nonetheless there are also many similarities between how individuals
experience color and it is possible to make very specific judgments about it 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 different
means and by using different materials (colorants). Displays, for instance, use colorants that emit red (long
wavelength), green (medium wavelength) and blue (short wavelength) light, where outputting a white color
requires the full use of 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 and because of this absorption, they are called subtractive. Typical
prints use cyan (red absorbing), magenta (green absorbing) and yellow (blue absorbing) inks as well as
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.
62 Chapter 6 Color management ENWW
Color management