HP Color LaserJet 4550 printer family - Software Technical Reference

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HP Color LaserJet 4550 Software Technical Reference 226
sending to the printer. This is unnecessary as the printer can do resampling after the image has been
transferred.
4.3 FREQUENTLY ASKED QUESTIONS
Why does the color look different on today's job or from the first to the last copy?
All electrophotographic printers can vary in the way they deposit toner onto the paper from one period to the next
due to a variety of environmental factors:
• environmental changes in the room where the printer is located
• changes in the environment inside the printer during operation
• different moisture content of the paper.
These environmental changes affect the electronic charge of the toner and the drum which results in very small
changes in the amount of toner deposited on the paper. This can cause subtle differences in the color on the
page. In general, these color differences are not objectionable, especially with images that include a wide mix of
colors. Typically, very small color shifts are lost in the overall look of the image.
However, changes in light, flat color areas, especially neutral grays, can become noticeable. Neutral gray colors
are those caused by mixing several colors together to generate a shade of gray. An example of this is a Windows
menu or tool bar. The differences are also more noticeable in areas with very low amounts of color, where small
differences can represent a relatively larger percentage change.
Despite onboard calibration and other techniques that HP uses to minimize these small effects, very small
variations in color are an inherent part of electrophotographic printing technology.
Why is the color quality poor or not what I expected?
There are many possible reasons why the color just does not look "right." Unfortunately, color does not have a
hard scientific definition. Consequently, different devices handle color in different ways.
• Color scanners, for example, can render identical pictures differently; these scanning differences affect the
final output.
• Monitors vary in the way they render color onscreen; adjustments to color settings can add to color variations.
As a result, color generated directly on the computer can look different on different computers. (See the next
question, Why don't the printed colors match the colors on the screen?)
• Software applications can process or display color in different ways and can change the appearance of color
images.
• Surrounding light affects the way color look, often causing significant differences in appearance from one light
source to the other.
• All RGB color data is not the same, which is why different applications can generate different results.
• The color "numbers" can be the same, an individual's perception can vary according to the circumstances.
When all operations are performed under one roof in one location, the scanner, the applications, the monitor, and
the printers can be tuned to each other by selecting settings that optimize the color match to the final printed
output. However, once the document is exchanged from one operation to another, the color can change because
the values for each color are encoded without a constant reference point.
To minimize problems associated with the different interpretation of color, Hewlett-Packard, in conjunction with
Microsoft, developed the sRGB color rendering space to provide a fixed reference point for color used in the
office. Because sRGB represents color the way most color monitors do, it is possible to use it to calibrate all
devices together. Use sRGB as the target for your scanners, your application program defaults, and your printed