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PPA Printer calibration for pnm2ppa
The pnm2ppa project team ppa-rpms@users.sourceforge.net
v0.4, October 28, 2000
Information and instructions for printer calibration using pnm2ppa.
http://sourceforge.net/projects/pnm2ppa (Updated for pnm2ppa-1.02 and
later.)
Overview of Printer Calibration.
There are three main tasks you may need to carry out to fine-tune your
PPA printer:
o Adjust the x-offset and y-offset to correctly center the printed
page on the paper
o Adjust the relative offsets between black and colored ink printing
- this should be done each time you replace an ink cartridge.
o Match the colors of printed images to some other output device -
this is color correction and is described in COLOR.html (or
COLOR.txt).
These instructions assume that you are already able to print
postscript files with your PPA printer. If your print filters are
properly configured, something like "lpr test.ps" will successfully
invoke ghostscript and pnm2ppa to print the postscript file test.ps.
Alternatively, you may be using shell scripts like "lprbw", "lprcolor"
and "lpreco" supplied with the pnm2ppa source code, and modified by
you for your defaults; you may also have defined special printing
devices in /etc/printcap, e.g. a "coloreco" device so you print with
lpr -P coloreco test.ps. These details vary with the operating
system and distribution you use.
(1) Centering the printed page on the paper.
This is done by adjusting the x-offset and y-offset parameters xoffset
and yoffset in the pnm2ppa configuration file (usually
/etc/pnm2ppa.conf). The parameters are given in units of 1/600 inch;
increasing xoffset moves the image to the right, and increasing
yoffset moves it downwards. These offsets now have default values
defined for each printer model, and you will probably not need to
adjust them. Uncomment and make small adjustments to the default
values for these in the configuration file, until the printout is
satisfactory. (You can also use the '-x' and '-y' command-line
parameters.)
There are two ways to check the offsets.
o either using the "calibrate_ppa" program.
o or printing a suitable test page.
The "calibrate_ppa" program is a stand-alone program distributed with
pnm2ppa which creates various test patterns in the raw pixmap format
accepted by pnm2ppa. (The three paper sizes, US Letter, US Legal, and
A4, are supported). If your paper size is A4, and your printer filter
accepts the "-l" (direct output) option to lpr, the command to run is:
calibrate_ppa -s a4 --center | pnm2ppa --bw -i - -o - | lpr -l
(Substitute "letter" or "legal" for "a4" to change the papersize; if
no paper size is specified, it is assumed to be letter.)
If "lpr -l" is not valid, you need to know which port your printer is
attached to. Assuming it is /dev/lp0, the above command becomes
calibrate_ppa -s a4 --center | pnm2ppa --bw -i - -o /dev/lp0.
The pattern shows distances from the edge of the printed page in
units of 50 dots (1/12 inch), and diagonal lines that should point to
the corners. Change xoffset and yoffset in the configuration file
(usually /etc/pnm2ppa.conf to center the pattern. The configuration
file is supplied with commented-out entries like #xoffset 160 showing
the default value. Remove the "#" to activate the entry.
In Red Hat or Mandrake Linux distributions, a suitable test page is
/usr/lib/rhs/rhs-printfilters/testpage.ps (US Letter paper) or
/usr/lib/rhs/rhs-printfilters/testpage-a4.ps (A4 paper). (If these
are not available, similar test pages are supplied in the pnm2ppa
source distribution.) These pages have margins drawn at standard
distances from the edges of the paper, and can also be used to check
the centering, but are not as accurate
(2) Calibrating the X and Y Color Head Offsets.
The color ink offsets now have to be calibrated with respect to the
black ink. Because the relative position of the two ink cartridges
can move slightly, this must be done whenever an ink cartridge is
removed and replaced.
To print an alignment calibration pattern on a4 paper, run
calibrate_ppa -s a4 --align | pnm2ppa --fd -i - -o - | lpr -l
On the printed page, there are four alignment patterns, corresponding
to configuration file parameters ColOffsX, ColOffsY, colorshear and
blackshear. The central alignment patterns, labelled "0" should be
perfectly aligned. If they are not, first correct the shearing
patterns, (see below). Then identify the best-aligned ColOffsX and
ColOffsY patterns, and add or subtract the positive or negative
number below the pattern from the value in the configuration file.
Check the result by printing the alignment test pattern:
calibrate_ppa --test | pnm2ppa -fd -i - -o - | lpr -l
The lines in the cross and square should be perfectly straight now.
The calibration can also be done by printing the test page test.ps
(found in the tarball pnm2ppa-1.0.tar.gz; or installed with the
pnm2ppa documentation. (This is often in /usr/doc/pnm2ppa*/.)
On the printout you see several images:
o top left, you see a square with both black and colored items.
These should align correctly, or you have to change your settings.
o You see a large vertical bar, and also a horizontal bar. On the
sides of the vertical bar there are a blue and a green line.
These should align with the 0 mark.
o You also see a small vertical, and horizontal, bar, with a red bar
on its side.
If these items do NOT line up, you should take the following steps:
o (1) take for the large bar the number of the tickmark just smaller
than the place where the green and blue lines point to. The minor
tick marks are 25 points.
o (2) To this number, add the number of the tick mark at which a red
tick mark exactly lines up. This might not work if the offsets are
way off; in that case, apply the correction of step 1, and print
again.
o (3) Add the horizontal offset to the value of ColOffsX, and the
vertical offset to the value of ColOffsY in the configuration file.
Now you can print test.ps again to see whether this procedure worked.
Shearing adjustments
If bidirectional printing causes "shearing" of vertical lines
(horizontal offsets of those parts of the line printed by left-to-
right print-head sweeps relative to those printed on right-to-left
sweeps) you can make small adjustments (in 1/600 inch) units using the
blackshear and colorshear parameters in the configuration file. You
can also suppress bidirectional printing with a unimode 1
configuration file entry.
The third and fourth lines on the color head offset calibration page
(see above) correspond to color and black print head shearing
corrections. If the central alignment patterns (labeled "0") are not
aligned, add or subtract the positive or negative number below the
best-aligned pattern from the colorshear and blackshear values in the
configuration file.
Cleaning the Print Heads
You can use calibrate_ppa to clean the print heads by printing
patterns that exercise all the ink nozzles:
calibrate_ppa --clean | pnm2ppa -p -i - -o - | lpr -l
calibrate_ppa --clean | pnm2ppa --bw -i - -o - | lpr -l
The first of these commands prints a cleaning pattern with colored
ink, the second uses black ink.
Other adjustments
The parameter blackness adjusts the number of black ink drops printed
per pixel. It takes values 1, 2, 3, or 4 (2 is the default). Other
values, like 0, suppress black ink.
Inks can also be suppressed by configuration file entries black_ink 0,
color_ink 0, cyan_ink 0, magenta_ink 0, or yellow_ink 0. These are
mainly useful for debugging the printer driver.
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