gs-pcl3.ref

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and driving a printer which sends them).
In these cases you should not specify <userinput>-dCUPSAccounting</userinput>.
</para></listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-dCUPSMessages<optional>=<replaceable>boolean</replaceable></optional></userinput></term>
<listitem><para>
Specify this parameter when using <command>pcl3</command> as a
component in a CUPS (Common UNIX Printing System) driver.
It will modify the format of error messages and warnings as expected by CUPS.
The default for this parameter is <userinput>false</userinput>.
</para></listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-dDepletion=<replaceable>depletion</replaceable></userinput></term>
<listitem><para>
This option is only available for old DeskJets
(including <userinput>unspecold</userinput>)
and when printing in colour.
The integer <replaceable>depletion</replaceable> controls an algorithm for
removing certain pixels from the image;
this leads to less ink being applied to the medium.
The possible values for <replaceable>depletion</replaceable> are:

<informaltable><tgroup cols="2">
<colspec align="right"><colspec align="left">
<tbody>
<row><entry><userinput>1</userinput></entry>
  <entry>No depletion</entry></row>
<row><entry><userinput>2</userinput></entry>
  <entry>25%</entry></row>
<row><entry><userinput>3</userinput></entry>
  <entry>50%</entry></row>
<row><entry><userinput>4</userinput></entry>
  <entry>25% with gamma correction</entry></row>
<row><entry><userinput>5</userinput></entry>
  <entry>50% with gamma correction</entry></row>
</tbody></tgroup></informaltable>

The default value is derived from
<option>Medium</option> and <option>PrintQuality</option>.
The values 4 and 5 are not understood by the DeskJet 500C,
but even for the other printers these values are not useful because PostScript
permits finer control for gamma correction through transfer functions
(see the subsection
<link linkend="TransferFunctions"><citetitle>Transfer Functions</citetitle ></link>
in the next section).
</para></listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-dDryTime=<replaceable>delay</replaceable></userinput></term>
<listitem><para>
With the exception of the DeskJets 500 and 500C,
series-500 DeskJet printers can be told to guarantee a minimum drying time of
<replaceable>delay</replaceable>
seconds before the next page of the same print job is dropped on a newly
printed page.
(This interval can be terminated by pressing the Load/Eject button.)
The printer will choose default values depending on the current print quality,
hence it is normally not necessary to specify this option and
the feature is even considered obsolete for post-series-500 DeskJets
although it is still supported by some of them.
</para>

<para>
Permissible values for
<replaceable>delay</replaceable>
are <userinput>null</userinput> and
integers in the range <userinput>0</userinput>
to <userinput>1200</userinput>,
where
<userinput>null</userinput>
instructs
<command>pcl3</command>
not to send a corresponding command,
<userinput>0</userinput>
establishes default values for the current print quality,
and all other values explicitly request the duration in seconds.
The default is <userinput>null</userinput>.
</para></listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-sDuplexCapability=<replaceable>capability</replaceable></userinput></term>
<listitem><para>
Looking at the final result (sheet printed),
there are two kinds of duplex printing identified by the two possible values
for the option <option>Tumble</option>.
Not all printers capable of duplex printing, however, provide the hardware
support necessary for both,
hence the driver must be told what the printer offers in order to be able to
compensate for the missing functionality.
The parameter <userinput><replaceable>capability</replaceable></userinput>
can be any of the following:

<informaltable><tgroup cols="2">
<colspec align="left"><colspec align="left">
<tbody>
<row><entry><userinput>none</userinput></entry>
  <entry>no duplex capability</entry></row>
<row><entry><userinput>sameLeadingEdge</userinput></entry>
  <entry>second pass of sheet occurs with the same leading edge</entry></row>
<row><entry><userinput>oppositeLeadingEdge</userinput></entry>
  <entry>second pass of sheet occurs with the opposite leading edge</entry></row>
<row><entry><userinput>both</userinput></entry>
  <entry>second pass of sheet can occur with either edge</entry></row>
</tbody></tgroup></informaltable>

This option can only be specified for
<userinput>unspecold</userinput> and <userinput>unspec</userinput>.
The default value is <userinput>none</userinput>.
</para>

<para>
The correct setting for the HP DeskJet 970C is
<userinput>oppositeLeadingEdge</userinput>,
but the printer permits access to its duplex functionality only if you specify
in addition
<userinput>-sPJLLanguage=PCL3GUI -dOnlyCRD</userinput>.
(Many thanks to Dawei W. Dong for an extensive series of experiments.)
</para>

<para>
If a printer does not offer hardware support for both orientations,
the document to be printed must execute <literal>showpage</literal> after a
possible page-level <literal>restore</literal> and not before,
otherwise the driver will not be able to compensate for the missing
functionality
and only one of the two <option>Tumble</option> values will work.
All DSC-3.0-conforming PostScript files have the required property.
<!-- See DSC 3.0, section 4.3 "Constraints", subsection "Use of showpage". -->
</para></listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-sIntensityRendering=<replaceable>method</replaceable></userinput></term>
<listitem><para>
Most printers,
including every PCL-3+ printer I know of,
can render only a small number of intensities per pixel and colorant.
In the most frequent case, merely two levels are possible.
As this is usually not sufficient,
various methods have been devised to achieve a larger palette;
this is possible at the expense of spatial resolution.
Because of this tradeoff between effective resolution and the number of
colours which can be distinguished,
the best method for a given document depends on the contents of the document
and the user should therefore be able to select it.
</para>

<para>
The <command>pcl3</command> driver supports the following
<userinput><replaceable>methods</replaceable></userinput> for intensity
rendering:

<informaltable><tgroup cols="2">
<colspec align="left"><colspec align="left">
<tbody>
<row><entry><userinput>printer</userinput></entry>
  <entry>use the printer's capabilities directly</entry></row>
<row><entry><userinput>halftones</userinput></entry>
  <entry>use ghostscript's halftoning implementation</entry></row>
<row><entry><userinput>Floyd-Steinberg</userinput></entry>
  <entry>use Floyd-Steinberg error diffusion</entry></row>
</tbody></tgroup></informaltable>

The default method is <userinput>halftones</userinput>.
The methods differ only in their treatment of intensities which cannot be
represented directly by the printer.
If your document contains for example only black text,
they all produce the same result, albeit at different speeds.
</para>

<para>
With <userinput>printer</userinput>,
<command>pcl3</command> will cause everything to be painted
at the full hardware resolution but will have to map all colours to the nearest
levels the printer can represent directly.
For a CMY or CMYK printer with two intensity levels,
this results in just 8 useful colours per pixel.
This value is therefore usually only sensible for documents with a small number
of widely different saturated colours
where accurate colour reproduction is of minor importance but
achieving the highest possible resolution is essential.
Another possible application is the case of PostScript input which has already
been adapted to the printer's resolution and available intensity levels.
</para>

<para>
With <userinput>halftones</userinput>,
ghostscript will use what looks like standard PostScript halftoning algorithms.
For details, consult a PostScript manual.
However, you should know that ghostscript's current halftoning
implementation has some problems:
<itemizedlist>
<listitem><para>
The algorithm cannot handle different non-zero values for
<option>BlackLevels</option> and <option>CMYLevels</option>.
In this situation <command>gs</command> will in general assume
that the number of black levels available is equal to that for CMY levels.
Depending on which of the numbers is smaller, there will then either be unused
black levels or some will be used more than once.
<!-- VERIFIED: gs 5.10 -->
</para></listitem>
<listitem><para>
When you are using values larger than 2 for <option>BlackLevels</option> or
<option>CMYLevels</option>,
ghostscript does not discover by itself that it could now achieve the same
number of shades with smaller halftone cells.
</para></listitem>
<listitem><para>
Most of the ways of increasing the halftone screen frequency seem to fail.
I&nbsp;have been successful only with the somewhat pedestrian approach of
using threshold arrays,
and even that worked only for some cases.
<!-- VERIFIED: gs 5.50, 6.01 -->
</para></listitem>
<listitem><para>
For particular CMYK values and with ghostscript version&nbsp;6 or higher,
the colour becomes drastically wrong.
One example is CMYK = (0.99998472, 0.002549, 0, 0.00367827);
this should be almost a pure cyan but is instead displayed as a sort of pink.
If one subtracts one unit in the last position for any of the non-zero
components,
the result becomes acceptable.
The problem has not been observed with ghostscript&nbsp;5.50.
</para></listitem>
<listitem><para>
For ghostscript versions up to and including 5.50,
if you are using the colour model <userinput>CMYK</userinput>
and more than 2 black levels you should not set merely a single halftone screen
(<literal>setscreen</literal>, a type-1 or a type-3 halftone dictionary)
because
ghostscript's dithering routine can in this case return non-monotonic levels of
black for monotonic input intensities.
<!--
  VERIFIED:
  Discovered with gs 5.10/hpdj at 4 levels using a 1-cell type-3 dictionary.
  Verified with gs 5.50.
  Also easily visible with a 2x2 line screen given to setscreen.
  Apparently gone with gs 6.01. -->
However, if you specify independent halftone information for the colour
components,
<command>gs</command>
uses a slower but more accurate algorithm instead which does not lead to the
wrong behaviour.
It is not necessary for the halftone information to be different for different
components to achieve this.
Note that ghostscript installs separate halftone screens for CMYK devices by
default if the resolution is at least 150 ppi.
<!-- VERIFIED: gs 5.10, 6.50 (definition of .sethireshalftone in gs_init.ps).
-->
</para></listitem>
</itemizedlist>
Whenever you modify the halftone screens you should therefore use a test file
like
<filename>levels-test.ps</filename> in the <command>pcl3</command> distribution
to check whether you obtain the desired result.
In particular,
you should count the number of intensities you can distinguish
for a single colorant:
if it is obviously not one plus
the number of pixels in the halftone cell times
one less than the number of hardware intensity levels,
something has gone wrong.
This is, for example, the case if
you specified 4 black levels and a 2&times;2 halftone cell,
and you then can distinguish more than 1 + 4&times;3 = 13 intensity levels.
You should also watch for non-monotonic jumps in intensity and incompletely
filled shapes.
</para>

<para>
The value <userinput>Floyd-Steinberg</userinput> selects Floyd-Steinberg error
diffusion as the method for rendering intensities.
Use this in particular for printing photographs and other documents with
a large number of colours or small irregular shapes.
Regrettably, <command>pcl3</command>'s speed is much slower with this
method than in the other cases,
hence this value should only be used when it is really needed
(e.g., when you run into one of ghostscript's halftoning problems)
or when the delay is acceptable.
</para>

<para>
If you are using ghostscript&nbsp;5.50 and
the page to be rendered needs a lot of memory
(this applies in particular to <userinput>Floyd-Steinberg</userinput> in colour)
a core dump may result under certain circumstances.
You can get around this by increasing the <option>MaxBitmap</option> parameter
or by switching to a newer ghostscript version.
</para>
</listitem>
</varlistentry>

<!-- ______________________________________________________________________ -->

<varlistentry>
<term><userinput>-dLeadingEdge=<replaceable>edge</replaceable></userinput></term>
<listitem><para>
This option can be used to specify which edge of the sheet will enter the
printer first.
The permitted values identify this edge by reference to
the orientation of default user space on the sheet
when printing with default settings (except for <option>LeadingEdge</option>)
and a page size having width &le; height
("canonical page in portrait orientation"):

<informaltable><tgroup cols="2">
<colspec align="right"><colspec align="left">
<tbody>	<!-- Copied from PLR3 p. 402. -->
<row><entry><userinput>null</userinput></entry>
  <entry>No request for media orientation</entry></row>
<row><entry><userinput>0</userinput></entry>
  <entry>Short edge; top of canonical page</entry></row>
<row><entry><userinput>1</userinput></entry>
  <entry>Long edge; right side of canonical page</entry></row>