<p>A CUPS PostScript printer driver consists of a PostScript Printer Description (PPD) file that describes the features and capabilities of the device, zero or more <em>filter</em> programs that prepare print data for the device, and zero or more support files for color management, online help, and so forth. The PPD file includes references to all of the filters and support files used by the driver.</p>
<p>Every time a user prints something the scheduler program, <ahref='man-cupsd.html'>cupsd(8)</a>, determines the format of the print job and the programs required to convert that job into something the printer understands. CUPS includes filter programs for many common formats, for example to convert Portable Document Format (PDF) files into device-independent PostScript, and then from device-independent PostScript to device-dependent PostScript. <ahref='#FIGURE_1'>Figure 1</a> shows the data flow of a typical print job.</p>
<p>The optional PostScript filter can be provided to add printer-specific commands to the PostScript output that cannot be represented in the PPD file or to reorganize the output for special printer features. Typically this is used to support advanced job management or finishing functions on the printer. CUPS includes a generic PostScript filter that handles all PPD-defined commands.</p>
<p>The optional port monitor handles interface-specific protocol or encoding issues. For example, many PostScript printers support the Binary Communications Protocol (BCP) and Tagged Binary Communications Protocol (TBCP) to allow applications to print 8-bit ("binary") PostScript jobs. CUPS includes port monitors for BCP and TBCP, and you can supply your own port monitors as needed.</p>
<p>The backend handles communications with the printer, sending print data from the last filter to the printer and relaying back-channel data from the printer to the upstream filters. CUPS includes backend programs for common direct-connect interfaces and network protocols, and you can provide your own backend to support custom interfaces and protocols.</p>
<p>The scheduler also supports a special "command" file format for sending maintenance commands and status queries to a printer or printer driver. Command print jobs typically use a single command filter program defined in the PPD file to generate the appropriate printer commands and handle any responses from the printer. <ahref='#FIGURE_2'>Figure 2</a> shows the data flow of a typical command job.</p>
<p>PostScript printer drivers typically do not require their own command filter since CUPS includes a generic PostScript command filter that supports all of the standard functions using PPD-defined commands.</p>
<h2class='title'><aname='CREATING'>Creating New PPD Files</a></h2>
<p>We recommend using the CUPS PPD compiler, <ahref='man-ppdc.html'>ppdc(1)</a>, to create new PPD files since it manages many of the tedious (and error-prone!) details of paper sizes and localization for you. It also allows you to easily support multiple devices from a single source file. For more information see the "<ahref='ppd-compiler.html'>Introduction to the PPD Compiler</a>" document. <ahref='#LISTING_1'>Listing 1</a> shows a driver information file for a black-and-white PostScript printer.</p>
<p>PostScript drivers require the attributes listed in <ahref='#TABLE_1'>Table 1</a>. If not specified, the defaults for CUPS drivers are used. A typical PostScript driver information file would include the following attributes:</p>
<tt>CMYK</tt>. If not specified, then <tt>RGB</tt> is
assumed.</td>
</tr>
<tr>
<td><tt>LandscapeOrientation</tt></td>
<td>The preferred landscape
orientation: <tt>Plus90</tt>, <tt>Minus90</tt>, or
<tt>Any</tt>. If not specified, <tt>Plus90</tt> is
assumed.</td>
</tr>
<tr>
<td><tt>LanguageLevel</tt></td>
<td>The PostScript language
level supported by the device: 1, 2, or 3. If not
specified, 2 is assumed.</td>
</tr>
<tr>
<td><tt>Product</tt></td>
<td>The string returned by
the PostScript <tt>product</tt> operator, which
<i>must</i> include parenthesis to conform with
PostScript syntax rules for strings. Multiple
<tt>Product</tt> attributes may be specified to support
multiple products with the same PPD file. If not
specified, "(ESP Ghostscript)" and "(GNU Ghostscript)"
are assumed.</td>
</tr>
<tr>
<td><tt>PSVersion</tt></td>
<td>The PostScript
interpreter version numbers as returned by the
<tt>version</tt> and <tt>revision</tt> operators. The
required format is "(version) revision". Multiple
<tt>PSVersion</tt> attributes may be specified to
support multiple interpreter version numbers. If not
specified, "(3010) 705" and "(3010) 707" are
assumed.</td>
</tr>
<tr>
<td><tt>TTRasterizer</tt></td>
<td>The type of TrueType
font rasterizer supported by the device, if any. The
supported values are <tt>None</tt>, <tt>Accept68k</tt>,
<tt>Type42</tt>, and <tt>TrueImage</tt>. If not
specified, <tt>None</tt> is assumed.</td>
</tr>
</table></div>
<h3>Query Commands</h3>
<p>Most PostScript printer PPD files include query commands (<tt>?PageSize</tt>, etc.) that allow applications to query the printer for its current settings and configuration. Query commands are included in driver information files as attributes. For example, the example in <ahref='#LISTING_1'>Listing 1</a> uses the following definition for the <tt>PageSize</tt> query command:</p>
<p>Normally a PostScript printer driver will not utilize any additional print filters. For drivers that provide additional filters such as a CUPS command file filter for doing printer maintenance, you must also list the following <tt>Filter</tt> directive to handle printing PostScript files:</p>
<p>The <tt>application/vnd.cups-command</tt> file type is used for CUPS command files. Use the following <tt>Filter</tt> directive to handle CUPS command files:</p>
<p>To use the standard PostScript command filter, specify <var>commandtops</var> as the path to the command filter.</p>
<h3>Custom PDF Filters</h3>
<p>The <tt>application/pdf</tt> file type is used for unfiltered PDF files while the <tt>application/vnd.cups-pdf</tt> file type is used for filtered PDF files. Use the following <tt>Filter</tt> directive to handle filtered PDF files:</p>
<p>Custom PDF filters that accept filtered data do not need to perform number-up processing and other types of page imposition, while those that accept unfiltered data MUST do the number-up processing themselves.</p>
<h3>Custom PostScript Filters</h3>
<p>The <tt>application/vnd.cups-postscript</tt> file type is used for filtered PostScript files. Use the following <tt>Filter</tt> directive to handle PostScript files:</p>
<h2class='title'><aname='COLOR'>Implementing Color Management</a></h2>
<p>CUPS uses ICC color profiles to provide more accurate color reproduction. The <ahref='spec-ppd.html#cupsICCProfile'><tt>cupsICCProfile</tt></a> attribute defines the color profiles that are available for a given printer, for example:</p>
<p>where "ColorModel.MediaType.Resolution" defines a selector based on the corresponding option selections. A simple driver might only define profiles for the color models that are supported, for example a printer supporting Gray and RGB might use:</p>
<p>macOS printer drivers can provide <ahref='spec-ppd.html#MACOSX'>additional attributes</a> to specify additional option panes in the print dialog, an image of the printer, a help book, and option presets for the driver software:</p>
