HP Color LaserJet 4700 series printer—Intelligent
calibration
Overview............................................................................................................................................ 2
Benefit ................................................................................................................................................ 2
How does it work? ............................................................................................................................... 2
Toner-level adjustment....................................................................................................................... 2
Determination of the turn on point................................................................................................... 2
Halftone correction ....................................................................................................................... 3
Strategically timed calibrations .......................................................................................................... 3
Self-timer feature .............................................................................................................................. 4
Overview
Color consistency is a primary customer requirement in many printing applications. Color consistency
is achieved when a print engine receives a signal requesting a certain amount of colorant (ink or
toner, for example) and then exactly applies that amount of colorant to a printed page. In practice,
the relationship between the requested amount of colorant and the amount actually produced can
vary. This variability is the primary factor leading to inconsistent color.
The following scenarios illustrate the importance of color consistency:

A user tries to make multiple copies of the same document. Are the colors the same on the first copy
as on the last?

A user prints a document and then several months later decides to print additional copies. Do the
copies look the same as the original?

A user printing a large job decides to split it across two printers. Do the colors from each of the
printers look the same?
Benefit
With intelligent color calibration, the HP Color LaserJet 4700 series printer provides color printing
that is consistent from page to page, regardless of the time between print jobs or the printing
environment. Intelligent color calibration is designed to occur automatically at intervals that maximize
printer availability.
How does it work?
The HP Color LaserJet 4700 series printer uses an intelligent calibration technology to achieve
consistent color in any environment. The technology has two basic components: toner-level adjustment
and strategically timed calibrations.
Toner-level adjustment
A calibration sequence measures toner patterns and feeds the results into a control system that adjusts
the amount of toner to a specified level. This adjustment is stored in the printer’s memory and applied
to every printed page.
Under normal printing conditions, printed images are transferred directly to paper, but during the
calibration sequence, the calibration image prints to the belt surface. The HP Color LaserJet 4700
series printer uses the surface of the electrostatic transfer belt as a reference point to make all
calibration adjustments. The calibration image can be easily cleaned from the belt prior to printing to
paper. Two sensors are strategically located near the belt surface to measure toner levels, and both
sensors are used simultaneously to reduce the calibration time.
During calibration, two adjustment types are performed: determination of the turn-on point and
halftone correction.
Determination of the turn on point
The first measurement determines the minimum toner level that can be printed, producing a barely
noticeable color. This is called the turn-on point, and it must be the same for all colors (cyan, yellow,
magenta, and black). The importance of the turn-on point is clear when printing highlights (very light
colors), because small variations in the amount of toner cause tremendous variations in the final color.
In Figure 1, below, the uncorrected turn-on point must be moved to the left in order to correspond with
the first point on the calibrated line. This process must be performed for each color: cyan, magenta,
yellow, and black.
2
For example, when printing a very light green color near the turn-on point., cyan and yellow toners
are used. If the cyan turns on late (or later than yellow)—as in the case of the uncorrected curve in
Figure 1—the resulting color displays a distinctly yellow tint. If both cyan and yellow turn on at the
same point—as shown on the calibrated curve—a true green results.
Halftone correction
The second adjustment is essentially the same thing as the first, except that it corrects the amount of
toner for all the halftone levels greater than the turn-on point. In Figure 1, this represents all the points
to the left of the uncorrected turn-on point. All of these points must be corrected, so they fall on the
calibrated line. This correction must be performed for each of the colors to ensure the correct resulting
color. For example, if a dark green is chosen and the applied level of yellow toner is greater than the
level of cyan toner, the resulting green appears to be more yellow.
Uncorrected Turn on Point
Toner Density %
Intelligent Halftone Calibration
100
90
80
70
60
50
40
30
20
10
0
0
Uncorrected
Calibrated
20
40
60
80
100
Halftone Level %
Figure 1. Intelligent halftone calibration
Strategically timed calibrations
Calibrations occur at set intervals, are strategically designed to maximize printer availability, and
may be initiated either automatically or manually from the control panel. Calibration occurs
automatically:

When the fuser temperature registers 122 degrees F (50 degrees C) or less at power on. If the
printer is powered off overnight, it performs a calibration when powered on. If the printer has been
in use (in Ready state), a calibration will not occur when the printer is turned off and on.

When a print cartridge is replaced.

At every 1,000-page interval after replacing a print cartridge.

With environmental condition changes. In some cases, a printer is subjected to widely variable
temperature and humidity conditions. When changes in either temperature or humidity reach a
certain point, a calibration sequence occurs.

When the electrostatic transfer belt is replaced.
3
Self-timer feature
A new self-timer feature improves printer availability. By entering the date and time in the control
panel, the printer can be automatically configured to wake up from sleep mode. If a printer goes into
sleep mode, sending a print job wakes it up. Normally when the printer wakes up, it requires a
minute or so to initialize and the user would have to wait until the initialization sequence was
complete before the job would finish. Using the self-timer allows customers to configure their printer to
wake and initialize during off hours, so initialization does not interfere with productivity.
4
© 2005 Hewlett-Packard Development Company, L.P. The information
contained herein is subject to change without notice. The only warranties for
HP products and services are set forth in the express warranty statements
accompanying such products and services. Nothing herein should be construed
as constituting an additional warranty. HP shall not be liable for technical or
editorial errors or omissions contained herein.
XXXX-XXXXEN, 05/2005