HP Color LaserJet 4550 printer family - Software Technical Reference

Readme files
HP Color LaserJet 4550 Software Technical Reference 227
output. Using sRGB will help you generate good color every time, both within your operating environment and
between different operating environments.
Why don't the printed colors match the colors on the screen?
The process of matching printer output color to your monitor is quite complex because printers and computer
monitors use different methods of producing color. Monitors display colors by adding the light from RGB (red,
green and blue) colored pixels using an additive color process. Printers print colors using a subtractive color
process that removes color from the viewing light source as it reflects through the CMYK (cyan, magenta, yellow,
and black) inks.
These two different color rendering processes have different color gamuts. Color gamut is the range of colors
that can be displayed. Matching the color from one color gamut to the other requires converting the colors.
Because some colors from each device are outside the gamut of the other device, it is impossible to match all the
colors exactly, resulting in some color shifts regardless of how well everything else is working.
Some of the main reasons that colors can not appear to match the screen are due to the monitor white point
setting, the color depth, the gamut mismatch and CMYK color conversions. In addition, the kind of lighting in the
room can affect the perception of color. A print viewed in sunlight will often look very different under incandescent
lighting.
White point setting
The white point setting of a monitor can have a dramatic affect on the color appearance of a displayed color. The
white point setting is easily modified on most monitors. Monitors are usually shipped with the white point set to
9300 degrees Kelvin, which has a very blue appearance. This can be seen by holding a piece of white paper,
illuminated by natural or indoor lighting, near a white part of the monitor display. The monitor will appear bluish
when compared to the paper.
The sRGB color space is designed for a 6500 Kelvin monitor white. Many monitors have a white setting that can
be changed with a user control. Choosing a 6500 K white point will produce optimum conditions for matching
printed colors with displayed colors.
Color bit depth
Display drivers and many applications provide controls over the bit depth of the color information. Whenever
possible, 24-bit color, or "Millions of Colors," should be chosen to avoid losing color information.
Monitor vs. printer gamuts
Because monitors display colors using an additive RGB (red, green and blue) color process but printers print
colors using a subtractive CMYK (cyan, magenta, yellow, and black) process, fundamental differences in the
colors possible on the devices exist.
As an example, in an additive color system, cyan (a light greenish-blue color) is displayed as a combination of
green and blue phosphors. In a subtractive color system, cyan is one of the primary colorants used on the print
and can be placed directly on the paper. The green and blue phosphors in a monitor combine to display a very
light and bright cyan color. The cyan used as a printing colorant is usually a darker color. A very light cyan would
not allow the printer to reproduce dark blue colors and would be unacceptable to most observers. This difference
in color primaries makes it extremely difficult to print a cyan that matches the monitor cyan perfectly.
In general, the differences in the color technology used in monitors and printers, and the ways the colors
combine, create very different gamuts or ranges of colors that can be produced. HP Color LaserJet printers have
proprietary technology to map the colors of the monitor into colors that can be printed in a manner that creates
excellent color output. Because of the monitor/printer gamut mismatch, some colors are moved from their
absolute color on the monitor to a color that can be printed.
CMYK Color Conversions