HP Designjet Z3100 Photo Printer series - Manual (Page 65)

To control the output of color imaging devices, the following color spaces are normally used:
● RGB (Red, Green, and Blue) is the color space typically used for additive devices. A color is
represented as a combination of specific quantities of red, green, and blue colorants and all such
combinations address the range of colors (color gamut) of the chosen device.
NOTE Subtractive devices can also be controlled using RGB data and, especially when
you do not require control over how you want to use your printer’s black ink, this is an efficient
option.
● CMYK (Cyan, Magenta, Yellow, and Black) is the color space for subtractive devices, such as
printers or presses. A color is represented as a combination of cyan, magenta, yellow, and black
(K) inks and all such combinations let you address the entire range of colors of the chosen device.
Both of these color spaces are only ways of controlling different color imaging devices and their values
do not describe colors directly. The same CMYK values, for example, will give different colors when
sent to different printers that use different inks and paper types. For example, consider a printer that
can use indoor inks or outdoor inks. The printer (hardware) is the same, but it has two different color
gamuts due to the different chemistry of the inks (dye-based versus pigmented). Furthermore, they need
to work with different paper types, as ink interaction with the paper depends on its chemistry. Thus, the
colors resulting from given CMYK values depend on the types of inks and papers that you use with a
printer. If this is the case using the same printer, you can easily imagine how different results can be
obtained with printers using different technologies and therefore using different ink chemistry.
The same happens with RGB-controlled devices. For example, imagine that two different monitors from
the same manufacturer have their white points at 9600 K and 6500 K respectively. Their colors are going
to be different because they will be related to a different white point reference. The situation is even
worse when comparing monitors from different manufacturers. As a recommendation, set the white point
of your monitor to 5000 K (also called D50), since this is the standard color temperature for the graphic
arts industries. If you dislike the appearance of D50 (you may find it too yellowish), the second choice
is to set the display to 6500 K (D65).
NOTE The white point is the brightest neutral color that a device can reproduce or that is present
in an image. The human visual system automatically adapts to the content of an image with
respect to its white point.
Furthermore, an RGB image, such as an image obtained from a digital camera and edited on a monitor,
needs to be first converted to CMYK for a specific printer before printing. Unfortunately different devices
do not give access to the same color gamuts: there are some colors that can be shown on a display
that cannot be matched in print and vice versa. The following graphic illustrates how colors visible to
the human eye are greater than those reproduced by a typical display or printer using a specific paper
type and also how the color gamuts accessible using these two color imaging devices do not match
each other.
ENWW The problem: color in the computer world 55
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