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<h1>Ghostscript and the PostScript Language</h1>
<h2><a name="toc"></a>Table of contents</h2>
<ul class="toc">
<li><a href="#Capabilities">Ghostscript's capabilities in relation to PostScript</a></li>
<li><a href="#Implementation_limits">Implementation limits</a></li>
<li>
<ul>
<li><a href="#Architectural_limits">Architectural limits</a></li>
<li><a href="#Typical_memory_limits">Typical memory limits in LanguageLevel 1</a></li>
<li><a href="#VM_consumption">Other differences in VM consumption</a></li>
</ul>
</li>
<li><a href="#Additional_operators">Additional operators in Ghostscript</a></li>
<li>
<ul>
<li><a href="#Graphics_and_text">Graphics and text operators</a></li>
<li>
<ul>
<li><a href="#Transparency">Transparency</a></li>
<li>
<ul>
<li><a href="#Transparency_graphics_state_operators">Graphics state operators</a></li>
<li><a href="#Transparency_rendering_stack_operators">Rendering stack operators</a></li>
<li><a href="#Transparency_ImageType">New ImageType</a></li>
</ul>
</li>
<li><a href="#Graphics_state">Other graphics state operators</a></li>
<li><a href="#Character">Character operators</a></li>
</ul>
</li>
<li><a href="#Other">Other operators</a></li>
<li>
<ul>
<li><a href="#Mathematical">Mathematical operators</a></li>
<li><a href="#Dictionary">Dictionary operators</a></li>
<li><a href="#Relational">Relational operators</a></li>
<li><a href="#File">File operators</a></li>
<li><a href="#Miscellaneous">Miscellaneous operators</a></li>
<li><a href="#Device">Device operators</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="#Filters">Filters</a></li>
<li>
<ul>
<li><a href="#Standard_filters">Standard filters</a></li>
<li><a href="#Non_standard_filters">Non-standard filters</a></li>
<li><a href="#Unstable_filters">Unstable filters</a></li>
</ul>
</li>
<li><a href="#Device_parameters">Device parameters</a></li>
<li><a href="#Banding_parameters">Banding parameters</a></li>
<li><a href="#User_parameters">User parameters</a></li>
<li><a href="#Miscellaneous_additions">Miscellaneous additions</a></li>
<li>
<ul>
<li><a href="#Extended_semantics_of_run">Extended semantics of 'run'</a></li>
<li><a href="#DecodingResources">Decoding resources</a></li>
<li><a href="#CIDDecodingResources">CIDDecoding resources</a></li>
<li><a href="#GlyphNames2Unicode">GlyphNames2Unicode</a></li>
<li><a href="#MultipleResourceDirectories">Multiple Resource directories</a></li>
</ul>
</li>
<li><a href="#PDF_scripting">Scripting the PDF interpreter</a></li>
<li>
<ul>
<li><a href="#PS_functions">PostScript functions</a></li>
<li><a href="#PDF_PS_operators">PostScript operators</a></li>
</ul>
</li>
</ul>
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<!-- [1.3 begin hint] ====================================================== -->
<p>For other information, see the <a href="Readme.htm">Ghostscript
overview</a>.</p>
<!-- [1.3 end hint] ======================================================== -->
<hr>
<!-- [1.0 end visible header] ============================================== -->
<!-- [2.0 begin contents] ================================================== -->
<h2><a name="Capabilities"></a>Ghostscript's capabilities in relation to PostScript</h2>
<p>
The Ghostscript interpreter, except as noted below, is intended to execute
properly any source program written in the (LanguageLevel 3)
<b>PostScript</b> language as defined in the <cite>PostScript
Language Reference, Third Edition</cite> (ISBN 0-201-37922-8) published by
Addison-Wesley in mid-1999. However, the interpreter is configurable in
ways that can restrict it to various subsets of this language.
Specifically, the base interpreter accepts the Level 1 subset of the
PostScript language, as defined in the first edition of the <cite>PostScript
Language Reference Manual</cite> (ISBN 0-201-10174-2) Addison-Wesley 1985,
plus the file system, version 25.0 language, and miscellaneous additions
listed in sections A.1.6, A.1.7, and A.1.8 of the Second Edition
respectively, including allowing a string operand for the
"<code>status</code>" operator. The base interpreter may be configured
(see the <a href="Make.htm">documentation on building Ghostscript</a> for
how to configure it) by adding any combination of the following:</p>
<ul>
<li>The ability to process PostScript Type 1 fonts. This facility is
normally included in the interpreter.</li>
<li>The CMYK color extensions listed in section A.1.4 of the Second Edition
(including <code>colorimage</code>). These facilities are available
only if the <code>color</code>, <code>dps</code>, or
<code>level2</code> feature was selected when Ghostscript was built.</li>
<li>The Display PostScript extensions listed in section A.1.3 of the Second
Edition, but excluding the operators listed in section A.1.2. These
facilities are available only if the <code>dps</code> feature or the
<code>level2</code> feature was selected when Ghostscript was built.</li>
<li>The composite font extensions listed in section A.1.5 of the Second
Edition, and the ability to handle Type 0 fonts. These facilities are
available only if the <code>compfont</code> feature or the
<code>level2</code> feature was selected when Ghostscript was built.</li>
<li>The ability to load TrueType fonts and to handle PostScript Type 42
(encapsulated TrueType) fonts. These facilities are available only if the
<code>ttfont</code> feature was selected when Ghostscript was built.</li>
<li>The PostScript Level 2 "filter" facilities except the
<code>DCTEncode</code> and <code>DCTDecode</code> filters. These
facilities are available only if the <code>filter</code>,
<code>dps</code>, or <code>level2</code> feature was selected when
Ghostscript was built.</li>
<li>The PostScript Level 2 <code>DCTEncode</code> and
<code>DCTDecode</code> filters. These facilities are available only if
the <code>dct</code> or <code>level2</code> feature was selected when
Ghostscript was built.</li>
<li>All the other PostScript Level 2 operators and facilities listed in
section A.1.1 of the Second Edition and not listed in any of the other
A.1.n sections. These facilities are available only if the
<code>level2</code> feature was selected when Ghostscript was built.</li>
<li>All PostScript LanguageLevel 3 operators and facilities listed in the
Third Edition, except as noted below. These facilities are available only
if the <code>psl3</code> feature was selected when Ghostscript was built.</li>
<li>The ability to recognize DOS EPSF files and process only the PostScript
part, ignoring bitmap previews or other information. This facility is
available only if the <code>epsf</code> feature was selected when
Ghostscript was built.</li>
</ul>
<p>
Ghostscript currently does not implement the following PostScript
LanguageLevel 3 facilities:</p>
<ul>
<li>Settable <code>ProcessColorModel</code> for page devices, except for
a very few special devices.</li>
<li><code>IODevice</code>s other than <code>%stdin</code>,
<code>%stdout</code>, <code>%stderr</code>, <code>%lineedit</code>,
<code>%statementedit</code>, <code>%os%</code>, and (if configured)
<code>%pipe%</code> and <code>%disk0%</code> through <code>%disk0%</code>.</li>
</ul>
<p>
Ghostscript can also interpret files in the Portable Document Format (PDF)
1.7 format defined in the
<a href="http://www.adobe.com/devnet/pdf/pdf_reference.html"><em>PDF
Reference</em> Version 1.7</a>,
distributed by <a href="http://www.adobe.com/">Adobe Systems
Incorporated</a>, except as noted below. This facility can be
disabled by deselecting the <code>pdf</code> feature
when Ghostscript is built.</p>
<p>
Ghostscript currently implements the majority of non-interactive
features defined in the PDF reference.</p>
<p>
Ghostscript also includes a number of
<a href="#Additional_operators">additional operators</a> defined below that
are not in the PostScript language defined by Adobe.</p>
<hr>
<h2><a name="Implementation_limits"></a>Implementation limits</h2>
<p>
The implementation limits show here correspond to those in Tables B.1 and
B.2 of the Second and Third Editions, which describe the quantities fully.
Where Ghostscript's limits are different from those of Adobe's
implementations (as shown in the Third Edition), Adobe's limits are also
shown.</p>
<h3><a name="Architectural_limits"></a>Architectural limits</h3>
<blockquote><table>
<tr><th colspan="4">Architectural limits (corresponds to Adobe table B.1)</th></tr>
<tr valign="bottom">
<th align="left">Quantity</th>
<th align="left">Limit</th>
<th align="left">Type</th>
<th align="left">Adobe</th></tr>
<tr valign="top"> <td>integer</td>
<td>32-bit</td>
<td>twos complement integer</td>
<td> </td></tr>
<tr valign="top"> <td>real</td>
<td>single-precision</td>
<td>IEEE float</td>
<td> </td></tr>
<tr valign="top"> <td>array</td>
<td>16777216</td>
<td>elements</td>
<td>65535</td></tr>
<tr valign="top"> <td>dictionary</td>
<td>16777215</td>
<td>elements</td>
<td>65535</td></tr>
<tr valign="top"> <td>string</td>
<td>16777216</td>
<td>characters</td>
<td>65535</td></tr>
<tr valign="top"> <td>name</td>
<td>16383</td>
<td>characters</td>
<td>127</td></tr>
<tr valign="top"> <td>filename</td>
<td>128*</td>
<td>characters</td>
<td> </td></tr>
<tr valign="top"> <td><code>save</code> level</td>
<td>none</td>
<td>(capacity of memory)</td>
<td>15</td></tr>
<tr valign="top"> <td><code>gsave</code> level</td>
<td>none</td>
<td>(capacity of memory)</td>
<td>13</td></tr>
</table></blockquote>
<p>
* The limit on the length of a file name is 128 characters if the name
starts with a %...% IODevice designation, or 124 characters if it does not.</p>
<h3><a name="Typical_memory_limits"></a>Typical memory limits in LanguageLevel 1</h3>
<blockquote><table>
<tr><th colspan="4">Memory limits (corresponds to Adobe table B.2)</th></tr>
<tr valign="bottom">
<th align="left">Quantity</th>
<th align="left">Limit</th>
<th align="left">Type</th>
<th align="left">Adobe</th></tr>
<tr valign="top"> <td><code>userdict</code></td>
<td>200</td>
<td> </td>
<td> </td></tr>
<tr valign="top"> <td><code>FontDirectory</code></td>
<td>100</td>
<td> </td>
<td> </td>
</tr>
<tr valign="top"> <td>operand stack</td>
<td>800</td>
<td> </td>
<td>500</td></tr>
<tr valign="top"> <td>dictionary stack</td>
<td>20</td>
<td> </td>
<td> </td>
</tr>
<tr valign="top"> <td>execution stack</td>
<td>250</td>
<td> </td><td> </td></tr>
<tr valign="top"> <td>interpreter level</td>
<td>none</td>
<td>(capacity of memory)</td>
<td>10</td></tr>
<tr valign="top"> <td>path</td>
<td>none</td>
<td>(capacity of memory)</td>
<td>1500</td></tr>
<tr valign="top"> <td>dash</td>
<td>11</td>
<td> </td>
<td> </td></tr>
<tr valign="top"> <td>VM</td>
<td>none</td>
<td>(capacity of memory)</td>
<td>240000</td></tr>
<tr valign="top"> <td>file</td>
<td>none</td>
<td>(determined by operating system)</td>
<td>6</td></tr>
<tr valign="top"> <td>image</td>
<td>65535</td>
<td>values (samples × components)<br>for 1-, 2-, 4-, or 8-bit samples</td>
<td>3300</td></tr>
<tr valign="top"> <td> </td>
<td>32767</td>
<td>values for 12-bit samples</td>
<td>3300</td></tr>
</table></blockquote>
<h3><a name="VM_consumption"></a>Other differences in VM consumption</h3>
<p>
In 32-bit builds packed array elements occupy either 2 bytes or 12 bytes.
The average element size is probably about 7 bytes. Names occupy 16 bytes plus the
space for the string.</p>
<p>
In 64-bit builds packed array elements occupy either 2 bytes or 16 bytes.
The average element size is probably about 9 bytes.
Names occupy 24 bytes plus the space for the string.</p>
<p>
The garbage collector doesn't reclaim portions of arrays obtained with
<tt>getinterval</tt>, rather it collects entire arrays.</p>
<hr>
<h2><a name="Additional_operators"></a>Additional operators in Ghostscript</h2>
<h3><a name="Graphics_and_text"></a>Graphics and text operators</h3>
<h4><u><a name="Transparency"></a>Transparency</u></h4>
<p><b><u>NOTE:</u></b> The following paragraphs describe non-standard operators
for accessing the PDF 1.4 and later transparent imaging model through Postscript.
If used incorrectly, they can have unexpected side effects and result in undefined
behavior. As a result, these operators are disabled when <a href="Use.htm#Safer"><b>SAFER</b></a>
is in force (as it is by default from version 9.50 onwards). To utilise these operators
you will either have to disable <code>SAFER</code> (<code>-dNOSAFER</code>) or use
the command line parameter <code>-dALLOWPSTRANSPARENCY</code>. The latter will make
the custom operators available, but leave the file access controls active.
<p>
Ghostscript provides a set of operators for implementing the transparency
and compositing facilities of PDF 1.4. These are defined only if the
<code>transpar</code> option was selected when Ghostscript was built. We
do not attempt to explain the underlying graphics model here: for details,
see <a
href="http://partners.adobe.com/asn/developer/technotes.html#acrobat-pdf"
class="offsite">Adobe
Technical Note</a> #5407, "<a
href="http://partners.adobe.com/asn/developer/acrosdk/DOCS/PDF_Transparency.pdf"
class="offsite">Transparency
in PDF</a>". Previously (in 9.52 and earlier), Ghostscript's model
maintained separate alpha and mask values for opacity and shape. This
model has been changed (as of 9.53) and instead Ghostscript maintains separate
float values for stroke and fill alpha values with a boolean that indicates
if these should be interpreted as shape or alpha values to be more in line with the
PDF specification.
</p>
<p>
What follows is a subset of all the custom operators related to transparency, but
covers the most useful, most common requirements.
</p>
<h5><a name="Transparency_graphics_state_operators"></a>Graphics state
operators</h5>
<p>Pushing the compositor device must be done before any other marking
operations are made on the current page, and must be done per page.
Popping the compositor should be done after the last marking operation
of the page, and before the call to <code>showpage</code>. Any marking
operations made after the compositor is popped will bypass the transparent
imaging model, and may produce unexpected output.
<dl>
<dt><code><depth> .pushpdf14devicefilter -</code></dt>
<dd>Installs the transparency compositor device into the graphics state. At
present the <code>depth</code> parameter should always be zero (<b>Subject
To Change.</b>)
</dl>
<dl>
<dt><code>- .popdf14devicefilter -</code></dt>
<dd>Removes (or, more accuracately, disables) the transparency compositor in
graphics state.
</dl>
<dl>
<dt><code><modename> .setblendmode -</code></dt>
<dd>Sets the blending mode in the graphics state. If the mode name is not
recognized, causes a <code>rangecheck</code> error. The initial value of
the blending mode is <code>/Compatible</code>.</dd>
</dl>
<dl>
<dt><code>- .currentblendmode <modename></code></dt>
<dd>Returns the graphics state blend mode on the stack.
</dl>
<dl>
<dt><code>[Deprecated as of 9.53] <0..1> .setopacityalpha -</code></dt>
<dd>Sets the opacity alpha value in the graphics state.
The initial opacity alpha value is 1. Note, it is strongly
suggested that this method not be used as it currently may
give inconsistent results when mixed with methods that
set stroke and fill alpha values. </dd>
</dl>
<dl>
<dt><code>[Deprecated as of 9.53] - .currentopacityalpha <0..1></code></dt>
<dd>Returns the graphics state opacity alpha on the stack. Note, it is strongly
suggested that this method not be used as it currently may
give inconsistent results when mixed with methods that
set stroke and fill alpha values.</dd>
</dl>
<dl>
<dt><code>[Deprecated as of 9.53] <0..1> .setshapealpha -</code></dt>
<dd>Sets the shape alpha value in the graphics state.
The initial shape alpha value is 1. Note, it is strongly
suggested that this method not be used as it currently may
give inconsistent results when mixed with methods that
set stroke and fill alpha values.</dd>
</dl>
<dl>
<dt><code>[Deprecated as of 9.53] - .currentshapealpha <0..1></code></dt>
<dd>Returns the graphics state shape alpha on the stack. Note, it is strongly
suggested that this method not be used as it currently may
give inconsistent results when mixed with methods that
set stroke and fill alpha values.</dd>
</dl>
<dl>
<dt><code><0..1> .setstrokeconstantalpha -</code></dt>
<dd>Sets the stroke alpha value in the graphics state.
The initial stroke alpha value is 1.</dd>
</dl>
<dl>
<dt><code> - .currentstrokeconstantalpha <0..1></code></dt>
<dd>Returns the graphics state stroke alpha value on the stack.</dd>
</dl>
<dl>
<dt><code><0..1> .setfillconstantalpha -</code></dt>
<dd>Sets the fill alpha value in the graphics state.
The initial fill alpha value is 1.</dd>
</dl>
<dl>
<dt><code> - .currentfillconstantalpha <0..1></code></dt>
<dd>Returns the graphics state fill alpha value on the stack.</dd>
</dl>
<dl>
<dt><code><bool> .setalphaisshape -</code></dt>
<dd>If true, the values set by setstrokeconstantalpha and setfillconstantalpha are interpreted as shape values.
The initial value of the AIS flag is <code>false</code>.</dd>
</dl>
<dl>
<dt><code> - .currentalphaisshape <0..1></code></dt>
<dd>Returns the graphics state alpha is shape (AIS) on the stack.</dd>
</dl>
<dl>
<dt><code><bool> .settextknockout -</code></dt>
<dd>Sets the text knockout flag in the graphics state.
The initial value of the text knockout flag is <code>true</code>.</dd>
</dl>
<dl>
<dt><code>- .currenttextknockout <bool></code></dt>
<dd>Returns the graphics state text knockout on the stack..</dd>
</dl>
<h5><a name="Transparency_rendering_stack_operators"></a>Rendering stack
operators</h5>
<p>
The interpreter state is extended to include a (per-context) rendering stack
for handling transparency groups and masks (generically, "layers"). Groups
accumulate a full value for each pixel (paint plus transparency); masks
accumulate only a coverage value. Layers must be properly nested, i.e., the
'end' or 'discard' operator must match the corresponding 'begin' operator.</p>
<p>
Beginning and ending groups must nest properly with respect to
<code>save</code> and <code>restore</code>: <code>save</code> and
<code>restore</code> do not save and restore the layer stack. Currently,
layers are not required to nest with respect to <code>gsave</code> and
<code>grestore</code>, except that the device that is current in the
graphics state when ending a layer must be the same as the device that was
current when beginning the layer. THIS AREA IS SUBJECT TO CHANGE.</p>
<dl>
<dt><code><paramdict> <llx> <lly> <urx> <ury>
.begintransparencygroup -</code></dt>
<dd>Begins a new transparency group. The <code>ll/ur</code> coordinates
are the bounding box of the group in the current user coordinate system.
<code>paramdict</code> has the following keys:</dd>
<dt><code>/Isolated</code></dt>
<dd>(optional) Boolean; default value = <code>false</code>.</dd>
<dt><code>/Knockout</code></dt>
<dd>(optional) Boolean; default value = <code>false</code>.</dd>
</dl>
<dl>
<dt><code>- .endtransparencygroup -</code></dt>
<dd>Ends the current transparency group, compositing the group being ended
onto the group that now becomes current.</dd>
</dl>
<dl>
<dt><code><cs_set?> <paramdict> <llx> <lly> <urx> <ury>
.begintransparencymaskgroup -</code></dt>
<dd>Begins a new transparency mask, which is represented as a group.
The <code>ll/ur</code> coordinates
are the bounding box of the mask in the current user coordinate system.
<code>paramdict</code> has the following keys:</dd>
<dt><code>/Subtype</code></dt>
<dd>(required) Name, either <code>/Alpha</code> or
<code>/Luminosity</code>.</dd>
<dt><code>/Background</code></dt>
<dd>(optional) Array of number.</dd>
<dt><code>/TransferFunction</code></dt>
<dd>(optional) Function object (produced by applying
<code>.buildfunction</code> to a Function dictionary).
<p>
The <code>cs_set</code> parameter is a boolean indicating whether the color
space for the mask group is the current color space in the graphics state, or
whether mask group color space should be inherited from the previous group
in the transparency group stack. In general, for the most consistent results,
it is recommended that this be set to <code>true</code>, and the intended
color space set in the graphics state prior to the <code>.begintransparencymaskgroup</code>
call.</p>
</dd>
</dl>
<dl>
<dt><code><mask#> .endtransparencymask -</code></dt>
<dd>Ends the current transparency mask group, compositing the mask group being ended
and setting it as the current soft mask in the graphics state.
<p>
The <code>mask#</code> parameter indicates whether the mask should be treated as
as opacity mask (<code>0</code>) or shape (<code>1</code>).
</dd>
</dl>
<h5><a name="Transparency_ImageType"></a>New ImageType</h5>
<p>
The transparency extension defines a new ImageType 103, similar to ImageType
3 with the following differences:</p>
<ul>
<li>The required <code>MaskDict</code> is replaced by two optional
dictionaries, <code>OpacityMaskDict</code> and
<code>ShapeMaskDict</code>. If present, these dictionaries must have a
<code>BitsPerComponent</code> entry, whose value may be greater than 1.
Note that in contrast to ImageType 3, where any non-zero chunky mask value
is equivalent to 1, ImageType 103 simply takes the low-order bits of chunky
mask values.</li>
<li>A <code>Matte</code> entry may be present in one or both mask
dictionaries, indicating premultiplication of the data values. If both
<code>MaskDict</code>s have a <code>Matte</code> entry and the values
of the two <code>Matte</code> entries are different, a
<code>rangecheck</code> error occurs.</li>
<li><code>InterleaveType</code> appears in the <code>MaskDict</code>s,
not the <code>DataDict</code>, because each mask has its own
<code>InterleaveType</code>. <code>InterleaveType</code> 2
(interlaced scan lines) is not supported.</li>
</ul>
<h4><a name="Graphics_state"></a>Other graphics state operators</h4>
<dl>
<dt><code><int> .setoverprintmode -</code></dt>
<dd>Sets the overprint mode in the graphics state. Legal values are 0 or 1.
Per the PDF 1.3 specification, if the overprint mode is 1, then when the
current color space is <code>DeviceCMYK</code>, color components whose
value is 0 do not write into the target, rather than writing a 0 value.
THIS BEHAVIOR IS NOT IMPLEMENTED YET. The initial value of the overprint
mode is 0.</dd>
</dl>
<dl>
<dt><code>- .currentoverprintmode <int></code></dt>
<dd>Returns the current overprint mode.</dd>
</dl>
<h4><a name="Character"></a>Character operators</h4>
<dl>
<dt><code><font> <charcode> %Type1BuildChar -</code></dt>
<dd>This is not a new operator: rather, it is a name known specially to the
interpreter. Whenever the interpreter needs to render a character (during
a ...<code>show</code>, <code>stringwidth</code>, or
<code>charpath</code>), it looks up the name <code>BuildChar</code>
in the font dictionary to find a procedure to run. If it does not find
this name, and if the <code>FontType</code> is 1, the interpreter
instead uses the value (looked up on the dictionary stack in the usual way)
of the name <code>%Type1BuildChar</code>.
<p>
The standard definition of <code>%Type1BuildChar</code> is in the
initialization file <code>gs_type1.ps</code>. Users should not need to
redefine <code>%Type1BuildChar</code>, except perhaps for tracing or
debugging.</p>
</dd>
</dl>
<dl>
<dt><code><font> <charname> %Type1BuildGlyph -</code></dt>
<dd>Provides the Type 1 implementation of <code>BuildGlyph</code>.</dd>
</dl>
<h3><a name="Other"></a>Other operators</h3>
<h4><a name="Mathematical"></a>Mathematical operators</h4>
<dl>
<dt><code><number> arccos <number></code></dt>
<dd>Computes the arc cosine of a number between -1 and 1.</dd>
</dl>
<dl>
<dt><code><number> arcsin <number></code></dt>
<dd>Computes the arc sine of a number between -1 and 1.</dd>
</dl>
<h4><a name="Dictionary"></a>Dictionary operators</h4>
<dl>
<dt><code>mark <key1> <value1> <key2> <value2> ... .dicttomark <dict></code></dt>
<dd>Creates and returns a dictionary with the given keys and values. This
is the same as the PostScript Level 2 <code>>></code> operator,
but is available even in Level 1 configurations.</dd>
</dl>
<dl>
<dt><code><dict> <key> .knownget <value> true</code></dt>
<dt><code><dict> <key> .knownget false</code></dt>
<dd>Combines <code>known</code> and <code>get</code> in the
obvious way.</dd>
</dl>
<h4><a name="Relational"></a>Relational operators</h4>
<dl>
<dt><code><number|string> <number|string> max <number|string></code></dt>
<dd>Returns the larger of two numbers or strings.</dd>
</dl>
<dl>
<dt><code><number|string> <number|string> min <number|string></code></dt>
<dd>Returns the smaller of two numbers or strings.</dd>
</dl>
<h4><a name="File"></a>File operators</h4>
<dl>
<dt><code><file> .fileposition <integer> true</code></dt>
<dd>Returns the position of <code>file</code>. Unlike the standard
<code>fileposition</code> operator, which causes an error if the file is
not positionable, <code>.fileposition</code> works on all files,
including filters: for non-positionable files, it returns the total number
of bytes read or written since the file was opened.</dd>
</dl>
<dl>
<dt><code><string> findlibfile <foundstring> <file> true</code></dt>
<dt><code><string> findlibfile <string> false</code></dt>
<dd>Opens the file of the given name for reading, searching through
directories <a href="Use.htm#Finding_files">as described in the usage
documentation</a>. If the search fails, <code>findlibfile</code> simply
pushes false on the stack and returns, rather than causing an error.</dd>
</dl>
<a name="Tempfile"></a>
<dl>
<dt><code><prefix_string|null> <access_string> .tempfile
<string> <file></code></dt>
<dd>Creates and opens a temporary file
like the <code>file</code> operator, also returning the file name. There
are three cases for the <code><prefix_string|null></code> operand:
<ul>
<li><code>null</code>: create the file in the same directory and with the
same name conventions as other temporary files created by the Ghostscript
implementation on this platform. E.g., the temporary file might be named
<code>/tmp/gs_a1234</code>.</li>
<li>A string that contains only alphanumeric characters, underline,
and dash: create the file in the standard temporary directory, but use
the
<code><prefix_string></code> as the first part of the file name.
E.g., if <code><prefix_string></code> is <code>xx</code>, the
temporary file might be named <code>/tmp/xxa1234</code>.</li>
<li>A string that is the beginning of an absolute file name: use the
<code><prefix_string></code> as the first part of the file name.
E.g., if <code><prefix_string></code> is
<code>/my/tmpdir/zz</code>, the temporary file might be named
<code>/my/tmpdir/zza1234</code>.
<p>
When running in <code>SAFER</code> mode, the absolute path must
be one of the strings on the permit file writing list
(see <a href="Use.htm#Safer"><b>-dSAFER</b></a>) .</p></li>
</ul>
</dd>
</dl>
<p>
Ghostscript also supports the following <code>IODevice</code> in
addition to a subset of those defined in the Adobe documentation:</p>
<ul>
<li>
<code>%pipe%command</code>, which opens a pipe on the given command.
This is supported only on operating systems that provide
<code>popen</code> (primarily Unix systems, and not all of those).</li>
<li>
<code>%disk#%</code>, which emulates the %disk0
through %disk9 devices on some Adobe PostScript printers. This pseudo
device provides a flat filenaming system with a user definable location
for the files (/Root). These devices will only be present if the
diskn.dev feature is specified during the build.
<p>This feature is intended to allow compatibility with font downloaders
that expect to store fonts on the %disk device of the printer.</p>
<p>
Use of the %disk#% devices requires that the location of files be given
by the user setting the /Root device parameter. The syntax for setting
the /Root parameter is:<pre>
mark /Root (directory_specification) (%disk#) .putdevparams
</pre>
For example, to store the files of the %disk0 device on the directory
/tmp/disk0, use:<pre>
mark /Root (/tmp/disk0/) (%disk0) .putdevparams
</pre></p>
<p>The files will be stored in the specified directory with arbitrary names.
A mapping file is used to store the association between the file
names given for the file operations on the %diskn# device and the file
that resides in the /Root directory.</p>
</li>
</ul>
<h4><a name="Miscellaneous"></a>Miscellaneous operators</h4>
<dl>
<dt><code><array> bind <array></code></dt>
<dd>Depending on the command line parameters <code>bind</code> is redefined as:</dd>
</dl>
<blockquote><table>
<tr valign="bottom">
<th valign="bottom" align="left">Flag</th>
<th valign="bottom" align="left">Definition</th></tr>
<tr valign="top"> <td>DELAYBIND</td>
<td>returns the argument, stores the argument for later use by <code>.bindnow</code></td></tr>
</table></blockquote>
<dl>
<dt><code><array> .bind <array></code></dt>
<dd>Performs standard <code>bind</code> operation as defined in PLRM regardless of
the DELAYBIND flag.</dd>
</dl>
<a name="bindnow"></a>
<dl>
<dt><code>- .bindnow -</code></dt>
<dd>Applies <code>bind</code> operator to all saved procedures after binding has been
deferred through -dDELAYBIND. Note that idiom recognition has no effect for the deferred
binding because the value returned from <code>bind</code> is discarded.
<p>
Since v. 8.12 <code>.bindnow</code> undefines itself and restores standard definition of
<code>bind</code> operator. In earlier versions after calling <code>.bindnow</code>,
the postscript <code>bind</code> operator needs to be rebound to the internal implementation
<code>.bind</code>, as in this fragment from the ps2ascii script:
<blockquote><pre><tt>DELAYBIND {
.bindnow
/bind /.bind load def
} if
</tt></pre></blockquote>
This is necessary for correct behavior with later code that uses the <code>bind</code> operator.</p>
</dd>
</dl>
<dl>
<dt><code><string> getenv <string> true</code></dt>
<dt><code><string> getenv false</code></dt>
<dd>Looks up a name in the shell environment. If the name is found,
returns the corresponding value and true; if the name is not found, returns
false.</dd>
</dl>
<dl>
<dt><code><string> <boolean> .setdebug -</code></dt>
<dd>Sets or clears any subset of the debugging flags included in
<code><string></code> based on the value of
<code><boolean></code>. These correspond to the debug
flags set by <code>-Z</code> on the command line and enable
debug and tracing output from various internal modules.
<p>Note that most tracing output is only produced if the Ghostscript
interpreter was built with the <code>DEBUG</code> preprocessor
symbol defined.</p>
<p>The <code>zsetdebug()</code> C function, which implements this
operator, is a useful breakpoint for debuggers.
Inserting '<code>() true .setdebug</code>' in the interpreted code will
trigger a breakpoint at that location without side effects. The
current flag state is available in C as the <code>gs_debug[]</code>
array, indexed by character value. The <code>zsetdebug</code> function will
be entered, and <code>gs_debug[]</code> updated, whether or not Ghostscript
is built with the <code>DEBUG</code> preprocessor symbol defined, so this
is useful even with release builds.</p>
</dd>
</dl>
<dl>
<dt><code>- .setsafe -</code></dt>
<dd>If Ghostscript is started with <code>-dNOSAFER</code> or
<code>-dDELAYSAFER</code>, this operator can be used to enter <b>SAFER</b>
mode (see <a href="Use.htm#Safer"><b>-dSAFER</b></a>)
<p>
<strong>The following is deprecated, see <a href="Use.htm#Safer"><b>-dSAFER</b></a></strong>
<p>
Since <b>SAFER</b> mode is implemented with userparameters and device parameters,
it is possible to use <code>save</code> and <code>restore</code> before
and after <code>.setsafe</code> to return to <b>NOSAFER</b> mode, but note
that such a save object is accessible to any procedures or file run in <b>SAFER</b> mode.
A malicious file with an unbalanced restore could potentially restore back to a point where
SAFER was not in operation.</p>
<p>
<b>Note: This uses setpagedevice to change .LockSafetyParams, so the page
will be erased as a side effect of this operator</b></p>
</dd>
</dl>
<dl>
<dt><code>- .locksafe -</code></dt>
<dd>
<p>
<strong>The following is deprecated, see <a href="Use.htm#Safer"><b>-dSAFER</b></a></strong>
<p>
This operator sets the current device's <code>.LockSafetyParams</code>
and the <code>LockFilePermissions</code> userparameter true as well as
adding the paths on LIBPATH and FONTPATH and the paths given by the
system params /GenericResourceDir and /FontResourceDir to the current
PermitFileReading list of paths.
<p>
If Ghostscript is started with <code>-dNOSAFER</code> or
<code>-dDELAYSAFER</code>, this operator can be used to enter <b>SAFER</b>
mode with the current set of <code>PermitFile...</code> user parameters
in effect. Since <code>.setsafe</code> sets the <code>PermitFile...</code>
user parameters to empty arrays, a script or job server that needs to
enable certain paths for file Reading, Writing and/or Control can use this
operator to perform the locking needed to enter <b>SAFER</b> mode.</p>
<p>
For example, to enable reading everywhere, but disallow writing and file
control (deleting and renaming files), the following can be used:</p>
<pre>
{ << /PermitFileReading [ (*) ]
/PermitFileWriting [ ]
/PermitFileControl [ ]
>> setuserparams
.locksafe
} stopped pop
</pre>
<p>In the above example, use of stopped will allow the use of this sequence on
older versions of Ghostscript where <code>.locksafe</code> was not an operator.</p>
<p>
<b>Note: This uses setpagedevice to change .LockSafetyParams, so the page
will be erased as a side effect of this operator</b></p>
<p>
See also <a href="#LockSafetyParams">.LockSafetyParams</a> and
<a href="#User_parameters">User Parameters</a>.</p>
</dd>
</dl>
<dl>
<dt><a name=".addcontrolpath"></a>
<code><name> <string> .addcontrolpath</code></dt>
<dd>
Adds a single path to the file access control lists.
<p>The <name> parameter can be one of:
<ul>
<li>
<p><code>/PermitFileReading</code>
</li>
<li>
<p><code>/PermitFileWriting</code>
</li>
<li>
<p><code>/PermitFileControl</code>
</li>
</ul>
<p>Whilst the string parameter is the path to be added to the requested list.
<p><strong>NOTE: Any attempt to call this operator after <a href="#activatepathcontrol">.activatepathcontrol</a>
has been called will result in a <code>Fatal</code> error, and the interpreter
will immediately exit.</strong>
</dd>
</dl>
<dl>
<dt><a name=".activatepathcontrol"></a>
<code>.activatepathcontrol</code></dt>
<dd>
Activates file access controls. Once activated, these access controls remain
in place until the interpreter shuts down.
</dd>
</dl>
<dl>
<dt><a name=".currentpathcontrolstate"></a>
<code>.currentpathcontrolstate</code></dt>
<dd>
Returns <code>true</code> on the operand stack if file access control has been
activated, <code>false</code> if not.
</dd>
</dl>
<dl>
<dt><a name=".genordered"></a>
<code><dict> .genordered <dict></code> (default: /OutputType /Type3).</dt>
<dt><code><dict> .genordered <string></code> (/OutputType /ThreshString).</dt>
<dt><code><dict> .genordered <array></code> (/OutputType /TOSArray).</dt>
<dd>This operator creates an ordered dither screening pattern with the parameters from the dictionary, returning (by default) a PostScript HalftoneType 3 (threshold array based) dictionary suitable for use with <code>sethalftone</code> or as a component Halftone of a <code>HalftoneType 5</code> Halftone dictionary. The /OutputType parameter can also select other than Halftone Type 3 as the return paramter,
<code><dict></code> has the following keys (all are optional):</dd>
<dt><code>/Frequency</code></dt>
<dd>Integer; default value = 75</dd>
<dt><code>/Angle</code></dt>
<dd>Integer; default value = 0</dd>
<dt><code>/HResolution</code></dt>
<dd>Real or Integer; default value is device X resolution.</dd>
<dt><code>/VResolution</code></dt>
<dd>Real or Integer; default value is device Y resolution.</dd>
<dt><code>/DotShape</code></dt>
<dd>Integer; default value = 0 (CIRCLE). Other shapes available are:</dd>
<dd> 1=REDBOOK, 2=INVERTED, 3=RHOMBOID, 4=LINE_X, 5=LINE_Y, 6=DIAMOND1, 7=DIAMOND2, 8=ROUNDSPOT,</dd>
<dt><code>/SuperCellSize</code></dt>
<dd>Integer; default value = 1 -- actual cell size determined by Frequency, Angle, H/V Resolution.</dd>
<dd>A larger value will allow more levels to be attained.</dd>
<dt><code>/Levels</code></dt>
<dd>Integer; default value = 1 -- actual number of gray levels is determined by Frequency and H/V Resolution.</dd>
<dd>SuperCellSize may need to be specified large enough to achieve the requested number of gray levels.</dd>
<dt><code>/OutputType</code></dt>
<dd>Name; default value = /Type3 (HalftoneType 3 dictionary). Other shapes available are:</dd>
<dt><code>/ThreshString</code></dt>
<dd>
First two bytes are width (high byte first), next two bytes are height, followed by the
threshold array bytes (same as /Thresholds of the Type3 dictionary).
</dd>
<dt><code>/TOSArray</code></dt>
<dd>
First element is the width, next is the height, followed by pairs X, then Y, of the turn-on-sequence of the threshold array. This information can be used to construct a threshold array with a transfer function "pickled into" the threshold array, which is useful if the turn-on-sequence has more than 256 pairs. Refer to toolbin/halftone/thresh_remap for more information.</dt>
</dd>
</dl>
<dl>
<dt><a name=".shellarguments"></a>
<code>.shellarguments</code></dt>
<dd>
<p>This operator is used to access the ARGUMENTS command line option.
<p>Relies on Ghostscript being called with the "--" command
line option - see <a href="Use.htm#Input_control">Input Control</a>
<p>See examples in lib for more information.
</dd>
</dl>
<h4><a name="Device"></a>Device operators</h4>
<dl>
<dt><code><device> copydevice <device></code></dt>
<dd>Copies a device. The copy is writable and installable. The copy is
created in the current VM (local or global), usually local VM for executing
ordinary PostScript files.</dd>
</dl>
<dl>
<dt><code><devicename> finddevice <device></code></dt>
<dd>Creates a default instance of a device specified by name. The instance
is created in global VM. If <code>finddevice</code> is called more than
once with the same device name, it creates the default instance the first
time, and returns the same instance thereafter.</dd>
</dl>
<dl>
<dt><code><devicename> findprotodevice <device></code></dt>
<dd>Finds the prototype of a device specified by name. A prototype can be
used with <code>getdeviceprops</code> or other parameter-reading
operators, but it is read-only and cannot be set with
<code>setdevice</code>: it must be copied first.</dd>
</dl>
<dl>
<dt><code><matrix> <width> <height> <palette> makeimagedevice <device></code></dt>
<dd>Makes a new device that accumulates an image in memory. <code>
matrix</code> is the initial transformation matrix: it must be orthogonal
(that is, [a 0 0 b x y] or
[0 a b 0 x y]). <code>palette</code> is a
string of 2^<small><sup><b>N</b></sup></small> or
3 × 2^<small><sup><b>N</b></sup></small> elements,
specifying how the 2^<small><sup><b>N</b></sup></small> possible pixel
values will be interpreted. Each element is interpreted as a gray value,
or as RGB values, multiplied by 255. For example, if you want a monochrome
image for which 0=white and 1=black, the palette should be
<code><ff 00></code>; if you want a 3-bit deep image with
just the primary colors and their complements (ignoring the fact that 3-bit
images are not supported), the palette might be <code><000000 0000ff
00ff00 00ffff ff0000 ff00ff ffff00 ffffff></code>. At present, the
palette must contain exactly 2, 4, 16, or 256 entries, and must contain an
entry for black and an entry for white; if it contains any entries that
aren't black, white, or gray, it must contain at least the six primary
colors (red, green, blue, and their complements cyan, magenta, and yellow);
aside from this, its contents are arbitrary.
<p>
Alternatively, palette can be 16, 24, 32, or null (equivalent to 24).
These are interpreted as:</p>
<blockquote><table>
<tr valign="bottom">
<th valign="bottom" align="left">Palette</th>
<th valign="bottom" align="left">Bits allocated per color</th></tr>
<tr valign="top"> <td>16</td>
<td>5 red, 6 green, 5 blue</td></tr>
<tr valign="top"> <td>24</td>
<td>8 red, 8 green, 8 blue</td></tr>
<tr valign="top"> <td>32</td>
<td>8C, 8M, 8Y, 8K</td></tr>
</table></blockquote>
<p>
Note that one can also make an image device (with the same palette as an
existing image device) by copying a device using the
<code>copydevice</code> operator.</p>
</dd>
</dl>
<dl>
<dt><code><device> <index> <string> copyscanlines <substring></code></dt>
<dd>Copies one or more scan lines from an image device into a string,
starting at a given scan line in the image. The data is in the same format
as for the <code>image</code> operator. It is an error if the device is
not an image device or if the string is too small to hold at least one
complete scan line. Always copies an integral number of scan lines.</dd>
</dl>
<dl>
<dt><code><device> setdevice -</code></dt>
<dd>
<p>
Sets the current device to the specified device. Also resets the
transformation and clipping path to the initial values for the device.
Signals an <code>invalidaccess</code> error if the device is a
prototype or if <a href="Language.htm#LockSafetyParams">.LockSafetyParams</a>
is true for the current device.</p>
<p>
Some device properties may need to be set with <tt>putdeviceprops</tt> before
<code>setdevice</code> is called. For example, the pdfwrite device will try
to open its output file, causing an <tt>undefinedfilename</tt> error if
<code>OutputFile</code> hasn't been set to a valid filename. Another
method in such cases is to use the level 2 operator instead:
<code><< /OutputDevice /pdfwrite /OutputFile
(MyPDF.pdf) >> setpagedevice</code>.</p></dd>
</dl>
<dl>
<dt><code>- currentdevice <device></code></dt>
<dd>Gets the current device from the graphics state.</dd>
</dl>
<dl>
<dt><code><device> getdeviceprops <mark> <name1> <value1> ... <namen> <valuen></code></dt>
<dd>Gets the properties of a device. See the section on
<a href="#Device_parameters">device parameters</a> below for details.</dd>
</dl>
<dl>
<dt><code><mark> <name1> <value1> ... <namen> <valuen> <device> putdeviceprops <device></code></dt>
<dd>Sets properties of a device. May cause <code>undefined</code>,
<code>invalidaccess</code>, <code>typecheck</code>, <code>rangecheck</code>, or
<code>limitcheck</code> errors.</dd>
</dl>
<hr>
<h2><a name="Filters"></a>Filters</h2>
<h3><a name="Standard_filters"></a>Standard filters</h3>
<p>
In its usual configuration, Ghostscript supports all the standard PostScript
LanguageLevel 3 filters, both encoding and decoding, except that it does not
currently support:</p>
<ul>
<li>the <code>EarlyChange</code> key in the <code>LZWEncode</code>
filter.</li>
</ul>
<p>
Ghostscript also supports additional keys in the optional dictionary
operands for some filters. For the <code>LZWDecode</code> filter:</p>
<dl>
<dt><code>InitialCodeLength <integer></code> (default 8)</dt>
<dd>An integer between 2 and 11 specifying the initial number of data bits
per code. Note that the actual initial code length is 1 greater than this,
to allow for the reset and end-of-data code values.</dd>
</dl>
<dl>
<dt><code>FirstBitLowOrder <boolean></code> (default false)</dt>
<dd>If true, codes appear with their low-order bit first.</dd>
</dl>
<dl>
<dt><code>BlockData <boolean></code> (default false)</dt>
<dd>If true, the data is broken into blocks in the manner specified for the
GIF file format.</dd>
</dl>
<p>
For the <code>CCITTFaxEncode</code> and <code>CCITTFaxDecode</code>
filters:</p>
<dl>
<dt><code>DecodedByteAlign <integer></code> (default 1)</dt>
<dd>An integer <b>N</b> with the value 1, 2, 4, 8, or 16, specifying that
decoded data scan lines are always a multiple of <b>N</b> bytes. The
encoding filter skips data in each scan line from Columns to the next
multiple of <b>N</b> bytes; the decoding filter pads each scan line to a
multiple of <b>N</b> bytes.</dd>
</dl>
<h3><a name="Non_standard_filters"></a>Non-standard filters</h3>
<p>
In addition to the standard PostScript LanguageLevel 3 filters, Ghostscript
supports the following non-standard filters. Many of these filters are used
internally to implement standard filters or facilities; they are almost
certain to remain, in their present form or a backward-compatible one, in
future Ghostscript releases.</p>
<dl>
<dt><code><target> /BCPEncode filter <file></code></dt>
<dt><code><source> /BCPDecode filter <file></code></dt>
<dd>Create filters that implement the Adobe Binary Communications Protocol.
See Adobe documentation for details.</dd>
</dl>
<dl>
<dt><code><target> <seed_integer> /eexecEncode filter <file></code></dt>
<dd>Creates a filter for encrypting data into the encrypted format described
in the Adobe Type 1 Font Format documentation. The
<code>seed_integer</code> must be 55665 for the <code>eexec</code>
section of a font, or 4330 for a <code>CharString</code>. Note that for
the <code>eexec</code> section of a font, this filter produces binary
output and does not include the initial 4 (or <code>lenIV</code>) garbage
bytes.</dd>
</dl>
<dl>
<dt><code><source> <seed_integer> /eexecDecode filter <file></code></dt>
<dt><code><source> <dict> /eexecDecode filter <file></code></dt>
<dd>Creates a filter for decrypting data encrypted as described in the Adobe
Type 1 Font Format documentation. The <code>seed_integer</code> must be
55665 or 4330 as described just above. PDF interpreters don't skip space characters
after operator <code>eexec</code>. Use <code>keep_spaces = true</code> for
decoding embedded PDF fonts. Recognized dictionary keys are:
<blockquote>
<code>seed <16-bit integer></code> (required)<br>
<code>lenIV <non-negative integer></code> (default=4)<br>
<code>eexec <bool></code> (default=<code>false</code>)<br>
<code>keep_spaces <bool></code> (default=<code>false</code>)
</blockquote>
</dd>
</dl>
<dl>
<dt><code><target> /MD5Encode filter <file></code></dt>
<dd>Creates a filter that produces the 16-byte MD5 digest of the input.
Note that no output is produced until the filter is closed.</dd>
</dl>
<dl>
<dt><code><source> <hex_boolean> /PFBDecode filter <file></code></dt>
<dd>Creates a filter that decodes data in <code>.PFB</code> format, the
usual semi-binary representation for Type 1 font files on IBM PC and
compatible systems. If <code>hex_boolean</code> is true, binary packets
are converted to hex; if false, binary packets are not converted.</dd>
</dl>
<dl>
<dt><code><target> <dict> /PixelDifferenceEncode filter <file></code></dt>
<dt><code><source> <dict> /PixelDifferenceDecode filter <file></code></dt>
<dd>Implements the Predictor=2 pixel-differencing option of the LZW
filters. Recognized keys are:
<blockquote>
<code>Colors <integer></code> (1 to 4, default=1)<br>
<code>BitsPerComponent <integer></code> (1, 2, 4, or 8, default=8)<br>
<code>Columns <integer></code> (>= 0, required)
</blockquote>
<p>
See the Adobe <a href="http://partners.adobe.com/public/developer/pdf/index_reference.html"><em>PDF Reference Manual</em></a> for details.</p>
</dd>
</dl>
<dl>
<dt><code><target> <dict> /PNGPredictorEncode filter <file></code></dt>
<dt><code><source> <dict> /PNGPredictorDecode filter <file></code></dt>
<dd><p>Implements the "filter" algorithms of the
<a href="http://www.libpng.org/pub/png/">Portable Network Graphics (PNG)
graphics format</a>. Recognized keys are:</p>
<blockquote><table>
<tr><th colspan="3">Keys recognized in PNG filter algorithms</th></tr>
<tr valign="bottom">
<th align="left">Key</th>
<th align="left">Range</th>
<th align="left">Default</th></tr>
<tr valign="top"> <td><code>Colors <integer></code></td>
<td>1 to 16</td>
<td>16</td></tr>
<tr valign="top"> <td><code>BitsPerComponent <integer></code></td>
<td>1, 2, 4, 8, or 16</td>
<td>8</td></tr>
<tr valign="top"> <td><code>Columns <integer></code></td>
<td>>= 0</td>
<td>1</td></tr>
<tr valign="top"> <td><code>Predictor <integer></code></td>
<td>10 to 15</td>
<td>15</td></tr>
</table></blockquote>
<p>
The <code>Predictor</code> is the PNG algorithm number + 10 for the
<code>Encoding</code> filter; the <code>Decoding</code> filter
ignores <code>Predictor</code>. 15 means the encoder attempts to
optimize the choice of algorithm. For more details see the PNG
specification</p>
<blockquote>
<a href="http://www.w3.org/TR/WD-png-960128.html">http://www.w3.org/TR/WD-png-960128.html</a>
</blockquote>
</dd>
</dl>
<dl>
<dt><code><target> /TBCPEncode filter <file></code></dt>
<dt><code><source> /TBCPDecode filter <file></code></dt>
<dd>Create filters that implement the Adobe Tagged Binary Communications
Protocol. See Adobe documentation for details.</dd>
</dl>
<dl>
<dt><code><target> /zlibEncode filter <file></code></dt>
<dt><code><source> /zlibDecode filter <file></code></dt>
<dd>Creates filters that use the data compression method variously known as
'zlib' (the name of a popular library that implements it), 'Deflate' (as in
<a href="http://www.ietf.org/rfc/rfc1951.txt">RFC 1951</a>, which is a
detailed specification for the method), 'gzip' (the name of a popular
compression application that uses it), or 'Flate' (Adobe's name). Note that
the PostScript <code>Flate</code> filters are actually a combination of
this filter with an optional predictor filter.</dd>
</dl>
<h3><a name="Unstable_filters"></a>Unstable filters</h3>
<p>
Some versions of Ghostscript may also support other non-standard filters for
experimental purposes. The current version includes the following such
filters, which are not documented further. No code should assume that these
filters will exist in compatible form, or at all, in future versions.</p>
<dl>
<dt><code><target/source> <string> ByteTranslateEncode/Decode filter <file></code></dt>
<dd><code>string</code> must be a string of exactly 256 bytes. Creates a
filter that converts each input byte <em>b</em> to
<code>string</code>[<em>b</em>]. Note that the <code>Encode</code>
and <code>Decode</code> filters operate identically: the client must
provide a <code>string</code> for the <code>Decode</code> filter that
is the inverse mapping of the <code>string</code> for the
<code>Encode</code> filter.</dd>
</dl>
<dl>
<dt><code><target/source> <dict> BoundedHuffmanEncode/Decode filter <file></code></dt>
<dd>These filters encode and decode data using Huffman codes. Since these
filters aren't used anywhere, we don't document them further, except to note
the recognized dictionary keys, which must be set identically for encoding
and decoding:
<blockquote>
<code>FirstBitLowOrder <bool></code> (default=false)<br>
<code>MaxCodeLength <int></code> (default=16)<br>
<code>EndOfData <bool></code> (default=true)<br>
<code>EncodeZeroRuns <int></code> (default=256)<br>
<code>Tables <int_array></code>
</blockquote>
</dd>
</dl>
<dl>
<dt><code><target/source> <dict> BWBlockSortEncode/Decode filter <file></code></dt>
<dd>This filter implements the Burroughs-Wheeler block sorting compression
method, which we've heard is also used in the popular <code>bzip2</code>
compression application. See <a
href="http://sources.redhat.com/bzip2/">http://sources.redhat.com/bzip2/</a>
for more information. The only recognized dictionary key is:
<blockquote>
<code>BlockSize <integer></code> (default=16384)
</blockquote>
</dd>
</dl>
<hr>
<h2><a name="Device_parameters"></a>Device parameters</h2>
Ghostscript supports the concept of device parameters for all devices, not
just page devices. (For non-page devices, these are accessible through
<code>getdeviceprops</code> and <code>putdeviceprops</code>, as
indicated above.) Here are the currently defined parameters for all
devices:
<dl>
<dt><a name="LockSafetyParams"></a>
<code>.LockSafetyParams <boolean></code></dt>
<dd>This parameter allows for improved system security by preventing
PostScript programs from being able to change potentially dangerous
device paramters such as OutputFile. This parameter cannot be set false
if it is already true.
<p>
If this parameter is true for the current device, attempt to set a new
device that has <code>.LockSafetyParams</code> false will signal an
<code> invalidaccess</code> error.</p>
</dd>
</dl>
<dl>
<dt><code>BitsPerPixel <integer> (usually read-only)</code></dt>
<dd>Number of bits per pixel.</dd>
</dl>
<dl>
<dt><code>.HWMargins [<four floats>]</code></dt>
<dd>Size of non-imageable regions around the edges of the page, in points
(units of 1/72in; see the <a href="Devices.htm#Measurements">notes on
measurements</a> in the documentation on devices).</dd>
</dl>
<dl>
<dt><code>HWSize [<integer> <integer>]</code></dt>
<dd>X and Y size in pixels.</dd>
</dl>
<dl>
<dt><code>%MediaSource <integer></code></dt>
<dd>The input tray key as determined by setpagedevice. PostScript
language programs don't set this parameter directly; they can
<em>request</em> a particular tray through the MediaPosition
setpagedevice parameter, but the setpagedevice logic need not
necessarily honor the request. Devices which support switchable trays
should implement %MediaSource in their put_params device procedure,
but (unlike most other such parameters) need not implement
corresponding reading logic in get_params.</dd>
</dl>
<dl>
<dt><code>%MediaDestination <integer></code></dt>
<dd>The output tray key as determined by setpagedevice. Handling by
devices should be parallel to %MediaSource.</dd>
</dl>
<dl>
<dt><code>.IgnoreNumCopies <boolean></code></dt>
<dd>Some page description languages support a NumCopies parameter.
This parameter instructs the device to ignore this, producing only
one copy of the document on output. Note that some devices ignore
NumCopies regardless because of limitation of the output format
or the implementation.</dd>
</dl>
<dl>
<dt><code>Name <string> (read-only)</code></dt>
<dd>The device name. Currently the same as <code>OutputDevice</code>.</dd>
</dl>
<dl>
<dt><code>Colors, GrayValues, RedValues, GreenValues, BlueValues, ColorValues (usually read-only)</code></dt>
<dd>As for the <code>deviceinfo</code> operator of Display PostScript.
<code>Red</code>, <code>Green</code>, <code>Blue</code>, and
<code>ColorValues</code> are only defined if
<code>Colors</code> > 1.</dd>
</dl>
<dl>
<dt><code>TextAlphaBits, GraphicsAlphaBits (usually read-only)</code></dt>
<dd>The number of bits of anti-aliasing information for text or graphics
respectively. Legal values are 1 (no anti-aliasing, the default for most
devices), 2, or 4.
<p>Because this feature relies upon rendering the input it is incompatible, and will generate
an error on attempted use, with any of the vector output devices.</p>
</dd>
</dl>
<p>
Ghostscript also supports the following read-only parameter that is not a
true device parameter:</p>
<dl>
<dt><code>.EmbedFontObjects <integer></code></dt>
<dd>If non-zero, indicates that the device may embed font objects (as
opposed to bitmaps for individual characters) in the output. The purpose of
this parameter is to disable third-party font renderers for such devices.
(This is zero for almost all devices.)</dd>
</dl>
<p>
In addition, the following are defined per Adobe's documentation for the
<code>setpagedevice</code> operator:</p>
<blockquote>
<code>Duplex</code> (if supported)<br>
<code>HWResolution</code><br>
<code>ImagingBBox</code><br>
<code>Margins</code><br>
<code>LeadingEdge</code><br>
<code>MediaPosition</code><br>
<code>NumCopies</code> (for printers only)<br>
<code>Orientation</code> (if supported)<br>
<code>OutputDevice</code><br>
<code>PageOffset</code> (write-only)<br>
<code>PageSize</code><br>
<code>ProcessColorModel</code> (usually read-only)<br>
</blockquote>
<p>
Some devices may only allow certain values for <code>HWResolution</code>
and <code>PageSize</code>. The null device ignores attempts to set
<code>PageSize</code>; its size is always <code>[0 0]</code>.</p>
<p>
It should be noted that calling <tt>setpagedevice</tt> with one of the above keys may reset the effects of any <code>pdfmark</code> commands up to that point. In particular this is true of HWResolution, a behavior that differs from Adobe Distiller.</p>
<a name="Banding_parameters"></a>
<p><b>
For raster printers and image format (jpeg*, tiff*, png* ...) devices these
page device parameters are also defined:</b></p>
<dl>
<dt><code>MaxBitmap <integer></code></dt>
<dd>Maximum space for a full page raster image (bitmap) in memory.
<p>This value includes the space for padding raster lines and for an array of
pointers for each raster line, thus the <code>MaxBitmap</code> value to allow
a given PageSize of a specific number of bits per pixel to be rendered in a
full page buffer may be somewhat larger than the bitmap size alone.</p>
</dd>
</dl>
<dl>
<dt><code>BandListStorage <file|memory></code></dt>
<dd>The default is determined by the make file macro <code>BAND_LIST_STORAGE</code>.
Since <code>memory</code> is always included, specifying <code>-sBandListStorage=memory</code>
when the default is <code>file</code> will use memory based storage for the
band list of the page. This is primarily intended for testing, but if the disk I/O is
slow, band list storage in memory may be faster.
</dd>
</dl>
<dl>
<dt><code>BufferSpace <integer></code></dt>
<dd>Size of the buffer space for band lists, if the full page raster image
(bitmap) is larger than <code>MaxBitmap</code> (see above.)
<p>The buffer space is used to collect display list (clist) commands for the
bands and then to consolidate those commands when writing the clist to the
selected BAND_LIST_STORAGE device (memory or file) set when Ghostscript is compiled.</p>
<p>If <code>MaxBitmap</code> (above) forces banding mode, and if <code>BufferSpace</code>
is large enough, the display list (clist) will consist of a single band.</p>
<p>The <code>BufferSpace</code> will determine the size of the 'consolidation'
buffer (above) even if the <code>MaxBitmap</code> value is low enough to force
banding/clist mode.</p>
</dd>
</dl>
<dl>
<dt><code>BGPrint <boolean></code></dt>
<dd>With many printer devices, when the display list (clist) banding mode is being used,
the page rendering and output can be performed in a background thread.
The default value, <code>false</code>, causes the rendering and printing to be
done in the same thread as the parser. When <code>-dBGPrint=true</code>, the
page output will be overlapped with parsing and writing the clist for the next page.
<p>If the device does not support background printing, rendering and printing will
be performed as if <code>-dBGPrint=false</code>.</p>
<p>Note that the background printing thread will allocate a band buffer (size determined
by the <code>BufferSpace</code> or <code>BandBufferSpace</code> values) in addition to
the band buffer in the 'main' parsing thread.</p>
<p>If <code>NumRenderingThreads</code> is > 0, then the background printing thread
will use the specified number of rendering threads as children of the background printing
thread. The background printing thread will perform any processing of the raster data
delivered by the rendering threads. Note that BGPrint is disabled for vector devices such as pdfwrite
and NumRenderingThreads has no effect on these devices eitehr.</p>
</dd>
</dl>
<dl>
<dt><code>GrayDetection <boolean></code></dt>
<dd>When <code>true</code>, and when the display list (clist) banding mode is being used,
during writing of the clist, the color processing logic collects information about the
colors used <b>before</b> the device color profile is applied. This allows special devices
that examine <code>dev->icc_struct->pageneutralcolor</code> with the information that all
colors on the page are near <i>neutral</i>, i.e. monochrome, and converting the rendered
raster to gray may be used to reduce the use of color toners/inks.
<p>
Since the determination of whether or not the page uses colors is determined before the
conversion to device colors, this information is independent of the device output profile.
The determination has a small delta (<tt>DEV_NEUTRAL</tt> and <tt>AB_NEUTRAL</tt> in
<tt>base/gscms.h</tt>) to allow colors close to neutral to be detected as neutral.
Changing this value requires rebuilding.</p>
<p>
Among the devices distributed with the source, currently only the <code>pnmcmyk</code>
device supports this parameter and will produce either a <code>P7 PAM</code> CMYK output
or a <code>P5 PGM</code> Gray output depending on the use of color on the page.</p>
<p>
Also, the 'pageneutralcolor' status can be interrogated as a device parameter of the
same name. Using PostScript there are several methods:</p>
<pre>
currentpagedevice /pageneutralcolor get
mark currentdevice getdeviceprops .dicttomark /pageneutralcolor get
/pageneutralcolor /GetDeviceParam .special_op { exch pop }{ //false } ifelse
</pre>
<p>
Note that the <tt>pageneutralcolor</tt> state is reset to <tt>false</tt> after the
page is output, so this parameter is only valid immediately <b>before</b> <tt>showpage</tt>
is executed, although the <tt>setpagedevice EndPage</tt> procedure can be used to check
the state just prior to the actual output of the page that resets <tt>pagenuetralcolor</tt>.
For example:</p>
<pre>
<< /EndPage {
exch pop 2 ne dup {
currentpagedevice /pageneutralcolor get (pageneutralcolor: ) print = flush
} if
}
>> setpagedevice
</pre>
<b>Notes:</b>
<p>
Since <code>-dGrayDetection=true</code> requires extra checking during
writing of the clist, this option should <b>only</b> be used for devices that
support the optimization of pages to monochrome, otherwise performance may be degraded
for no benefit.</p>
<p>
Since GrayDetection=true is only effective when in clist (banding) mode, it is recommended
to also force banding. For example: <b><tt>-dGrayDetection=true -dMaxBitmap=0</tt></b></p>
</dd>
</dl>
<dl>
<dt><code>NumRenderingThreads <integer></code></dt>
<dd>When the display list (clist) banding mode is being used, bands can be rendered
in separate threads. The default value, 0, causes the rendering of bands to be
done in the same thread as the parser and device driver. <code>NumRenderingThreads</code>
of 1 or higher results in bands rendering in the specified number of 'background'
threads.
<p>The number of threads should generally be set to the number of available
processor cores for best throughput.</p>
<p>Note that each thread will allocate a band buffer (size determined by the
<code>BufferSpace</code> or <code>BandBufferSpace</code> values) in addition to
the band buffer in the 'main' thread.</p>
<p>Additoinally note that ths parameter has no effect with devices which do not generally
render to a bitmap output, such as the vector devices (eg pdfwrite) and has no effect
when rendering, but not using a clist. See <a href="Use.htm#Improving_performance">Improving_performance</a>
</p>
</dd>
</dl>
<dl>
<dt><code>OutputFile <string></code></dt>
<dd>An empty string means "send to printer directly", otherwise specifies
the file name for output; <code>%d</code> is replaced by the page number
for page-oriented output devices;
on Unix systems <code>%pipe%</code><em>command</em> writes to a pipe.
(<code>|</code><em>command</em> also writes to a pipe, but is now
deprecated). Also see the <code>-o</code> parameter.
<p>
Attempts to set this parameter if <code>.LockSafetyParams</code> is true
will signal an <code>invalidaccess</code> error.</p>
</dd>
</dl>
<dl>
<dt><code>OpenOutputFile <boolean></code></dt>
<dd>If true, open the device's output file when the device is opened,
rather than waiting until the first page is ready to print.</dd>
</dl>
<dl>
<dt><code>PageCount <integer> (read-only)</code></dt>
<dd>Counts the number of pages printed on the device.</dd>
</dl>
<p>
The following parameters are for use only by very specialized applications
that separate band construction from band rasterization. <b>Improper use may
cause unpredictable errors.</b> In particular, if you only want to allocate
more memory for banding, to increase band size and improve performance, use
the <code>BufferSpace</code> parameter, not <code>BandBufferSpace</code>.</p>
<dl>
<dt><code>BandHeight <integer></code></dt>
<dd>The height of bands when banding. 0 means use the largest band height
that will fit within the <code>BandBufferSpace</code> (or <code>BufferSpace</code>,
if <code>BandBufferSpace</code> is not specified). If <code>BandHeight</code>
is larger than the number of lines that will fit in the buffer, opening the device will fail.
If the value is -1, the BandHeight will automatically be set to the page height
(1 band for the entire page). This is primarily for developers debugging clist issues.
</dd>
</dl>
<dl>
<dt><code>BandWidth <integer></code></dt>
<dd>The width of bands in the rasterizing pass, in pixels. 0 means use the
actual page width. A BandWidth value smaller than the width of the page
will be ignored, and the actual page width will be used instead.</dd>
</dl>
<dl>
<dt><code>BandBufferSpace <integer></code></dt>
<dd>The size of the band buffer in the rasterizing pass, in bytes. 0 means
use the same buffer size as for the interpretation pass.</dd>
</dl>
<p>
Ghostscript supports the following parameter for
<code>setpagedevice</code> and <code>currentpagedevice</code> that is
not a device parameter per se:</p>
<dl>
<dt><code>ViewerPreProcess <procedure></code></dt>
<dd>Specifies a procedure to be applied to the page device dictionary
before any other processing is done. The procedure may not alter the
dictionary, but it may return a modified copy. This "hook" is provided for
use by viewing programs such as GSview.</dd>
</dl>
<hr>
<h2><a name="User_parameters"></a>User parameters</h2>
Ghostscript supports the following non-standard user parameters:
<dl>
<dt><code>ProcessDSCComment <procedure|null></code></dt>
<dd>If not null, this procedure is called whenever the scanner detects a DSC
comment (comment beginning with <code>%%</code> or <code>%!</code>).
There are two operands, the file and the comment (minus any terminating
EOL), which the procedure must consume.</dd>
</dl>
<dl>
<dt><code>ProcessComment <procedure|null></code></dt>
<dd>If not null, this procedure is called whenever the scanner detects a
comment (or, if <code>ProcessDSCComment</code> is also not null, a
comment other than a DSC comment). The operands are the same as for
<code>ProcessDSCComment</code>.</dd>
</dl>
<dl>
<dt><code>LockFilePermissions <boolean></code></dt>
<dd>If <tt>true</tt>, this parameter and the three <tt>PermitFile...</tt>
parameters cannot be changed. Attempts to change any of the values
when LockFilePermissions is <tt>true</tt> will signal <code>invalidaccess</code>.
Also, when this value is <tt>true</tt>, the <code>file</code> operator
will give <code>invalidaccess</code> when attempting to open files
(processes) using the <code>%pipe</code> device.
<p>
Also when <code>LockFilePermissions</code> is <tt>true</tt>, strings
cannot reference the parent directory (platform specific). For example
<code>(../../xyz)</code> is illegal on unix, Windows
and Macintosh, and <code>([.#.#.XYZ])</code> is illegal on VMS.</p>
<p>
This parameter is set <tt>true</tt> by the <code>.setsafe</code> and
<code>.locksafe</code> operators.</p>
</dd>
</dl>
<dl>
<dt><code>PermitFileReading <array of strings></code></dt>
<dt><code>PermitFileWriting <array of strings></code></dt>
<dt><code>PermitFileControl <array of strings></code></dt>
<dd>These parameters specify paths where file reading, writing and the
'control' operations are permitted, respectively. File control
operations are <code>deletefile</code> and <code>renamefile</code>.
For <code>renamefile</code>, the filename for the current filename
must match one of the paths on the PermitFileControl list, and the
new filename must be on <b>both</b> the PermitFileControl and the
PermitFileWriting lists of paths.
<p>
The strings can contain wildcard characters as for the <code>filenameforall</code>
operator and unless specifying a single file, will end with a <b>*</b>
for directories (folders) to allow access to all files and sub-directories
in that directory.</p>
<p>
<b>Note:</b> The strings are used for stringmatch operations similar
to <code>filenameforall</code>, thus on MS Windows platforms, use the '/'
character to separate directories and filenames or use '\\\\' to
have the string contain '\\' which will match a single '\' in the
target filename (use of '/' is strongly recommended).</p>
<p>
The <a href="Use.htm#Safer"><b>SAFER</b></a> mode and the
<code>.setsafe</code> operator set all three lists to empty arrays,
thus the only files that can be read are the <code>%stdin</code> device and
on LIBPATH or FONTPATH or the Resource paths specified by the /FontResourceDir
or /GenericResourceDir system params. Files cannot be opened for writing
anywhere and cannot be deleted or renamed except for files created with the
<a href="#Tempfile"><b>.tempfile</b></a> operator).</p>
<p>
<b>Note: </b>Limiting file reading as above is <b>NOT</b> compatible with
SAFER mode in release versions before 7.11 and corresponds to the use of
<code>-dPARANOIDSAFER</code> in version 7.04 (up to and not including
version 7.10) and GPL versions 6.53 (up to and not including 6.60).</p>
</dd>
</dl>
<dl>
<dt><code>AlignToPixels <integer></code></dt>
<dd>Control sub-pixel positioning of character glyphs (where
applicable). A value of 1 specifies alignment of text characters to
pixels boundaries. A value of 0 to subpixels where the division factor
is set by the device parameter <code>TextAlphaBits</code>. If the
latter is 1, the same rendering results regardless of the value of
<code>AlignToPixels</code>. The initial value defaults to 1, but this
may be overridden by the command line argument
<code>-dAlignToPixels</code>.</dd>
</dl>
<dl>
<dt><a name="GridFitTT"></a>
<code>GridFitTT <integer></code></dt>
<dd>Control the use of True Type grid fitting.
Ghostscript, by default, uses Freetype for rendering Truetype (and most other) glyphs
(but other scaler/renderer libraries can be used), thus has access to a complete Truetype
bytecode interpreter.
<p>
This parameter controls the hinting of Truetype glyphs.</p>
<ul>
<li>
A value of 0 disables grid fitting for all True Type fonts (not generally recommended).
</li>
<li>
A value of 1 enables the grid fitting using the native Truetype hinting bytecode
program(s). Fonts or glyphs with faulty bytecode program(s) will be rendered unhinted.
</li>
<li>
A value 2 is scaler/renderer dependent (generally, if no alternative hinting engine is available
this will be equivalent to 1). With the Freetype (our default) this enables Freetype's built-in
autohinter.
</li>
<li>
With Freetype, a value of 3 is effectively equivalent to 1.
</li>
</ul>
<p>
This parameter defaults to 1, but this
may be overridden on the command line with
<code>-dGridFitTT=n</code>.</p>
</dd>
</dl>
<hr>
<h2><a name="Miscellaneous_additions"></a>Miscellaneous additions</h2>
<h3><a name="Extended_semantics_of_run"></a>Extended semantics of 'run'</h3>
<p>
The operator <code>run</code> can take either a string or a file as its argument. In
the latter case, it just runs the file, closing it at the end, and trapping
errors just as for the string case.</p>
<h3><a name="DecodingResources"></a>Decoding resources</h3>
<p>
<code>Decoding</code> is a Ghostscript-specific resource category. It contains
various resources for emulating PostScript fonts with other font technologies.
Instances of the <tt>Decoding</tt> category are tables which map PostScript glyph
names to character codes used with TrueType, Intellifont, Microtype and other font formats.</p>
<p>
Currently Ghostscript is capable of PostScript font emulation in 2 ways :</p>
<ul>
<li>
1. Through <a href="./Use.htm#FAPI_run">FAPI</a> plugins, and
</li>
<li>
2. With TrueType font files, using the native font renderer, by
specifying TrueType font names or files in <a href="../Resource/Init/Fontmap.GS">Resource/Init/Fontmap.GS</a>.
</li>
</ul>
<p>
<code>Decoding</code> resources are not currently used by the native font renderer.</p>
<p>
An instance of the <code>Decoding</code> resource category is
a dictionary. The dictionary keys are PostScript glyph names and the
values are either character codes, or arrays of character codes.
Arrays are used when a single name may be mapped to various character codes -
in this case Ghostscript tries all alternatives until a success.
The name of the resource instance should
reflect the character set for which it maps. For example,
<code>/Unicode</code> <code>/Decoding</code> resource maps to
Unicode UTF-16.</p>
<p>
The rules for using <code>Decoding</code> resources in particular
cases are specified in the configuration file
<a href="../Resource/Init/xlatmap">Resource/Init/xlatmap</a>. See the file itself for more
information.</p>
<p>
The file format for <code>Decoding</code> resource files is
generic PostScript.
Users may want to define custom <code>Decoding</code> resources.
The <code>ParseDecoding</code> procset defined in
<a href="../Resource/Init/gs_ciddc.ps">Resource/Init/gs_ciddc.ps</a> allows representation
of the table in a comfortable form.</p>
<h3><a name="CIDDecodingResources"></a>CIDDecoding resources</h3>
<p>
<code>CIDDecoding</code> resources are similar to <code>Decoding</code>
resources, except they map Character Identifiers (CIDs) rather than glyph names.
Another difference is that the native Ghostscript font renderer uses
<code>CIDDecoding</code> resources while emulate CID fonts with TrueType or OpenType fonts.</p>
<p>
An instance of the <code>CIDDecoding</code> resource category is
a dictionary of arrays. Keys in the dictionary are integers,
which correspond to high order byte of a CID.
Values are 256-element arrays, and their indices correspond to the low order byte of a CID.
Each elemet of an array is either null, or character code (integer), or an array
of character codes (integers). The zero code represents mapping to the default character.</p>
<p>
The dictionary includes the additional key <code>CIDCount</code>.
Its value is the maximal CID defined, plus one.</p>
<p>
The Ghostscript library is capable of generating some <code>CIDDecoding</code>
instances automatically, using the appropriate <code>CMap</code> (character map)
resources. This covers most of practical cases if the neccessary <code>CMap</code>
resources are provided. See the table <code>.CMapChooser</code> in
<a href="../Resource/Init/gs_ciddc.ps">Resource/Init/gs_ciddc.ps</a>
for the names of automatically gerenated resources and associated <code>CMap</code>s.
They allow to mapping CNS1, GB1, Japan1, Japan2 and Korea1 CID sets to TrueType
character sets known as Unicode (exactly UTF-16), Big5,
GB1213, ShiftJIS, Johab and Wansung.</p>
<p>
The file format for <code>CIDDecoding</code> resource file is
generic PostScript.
Users may want to define custom resources to <code>CIDDecoding</code>
resource category.</p>
<h3><a name="GlyphNames2Unicode"></a>GlyphNames2Unicode</h3>
<p>
<code>GlyphNames2Unicode</code> is an undocumented dictionary which Adobe
PostScript printer driver uses to communicate with Adobe Distiller.
In this dictionary the keys are glyph names, the values are Unicode UTF-16 codes for them.
The dictionaly is stored in the <code>FontInfo</code> dictionary under
the key <code>GlyphNames2Unicode</code>. Ghostscript recognises it and uses
to generate <code>ToUnicode</code> CMaps with pdfwrite.</p>
<h3><a name="MultipleResourceDirectories"></a>Multiple Resource directories</h3>
<p>
Since 8.10 release Ghostscript maintains multiple resource directories.</p>
<p>
Ghostscript does not distinguish <code>lib</code> and
<code>Resource</code> directories.
There is no file name conflicts because <code>lib</code> does not
contain subdirectories, but <code>Resource</code>
always store files in subdirectories.</p>
<p>
The search method with multiple resource directories
appears not fully conforming to PLRM. We cannot unconditionally call
<code>ResourceFileName</code> while executing <code>findresource</code>
or <code>resourcestatus</code>, <code>resourceforall</code>, because
per PLRM it always returns a single path. Therefore Ghostscript
implements an extended search method in <code>findresource</code>,
<code>resourcestatus</code> and <code>resourceforall</code>, which
first calls <code>ResourceFileName</code> and checks whether the
returned path points to an existing file. If yes, the file is used,
othervise Ghostscript searches all directories specified in
<code>LIB_PATH</code>. With a single resource directory
it appears conforming to PLRM and equivalent to Adobe implementations.</p>
<p>
<code>ResourceFileName</code> may be used for obtaining a path
where a resource file to be installed. In this case
Ghostscript to be invoked with <code>-sGenericResourceDir=path</code>,
specifying an absolute path. The default value for
<code>GenericResourceDir</code> is a relative path. Therefore
a default invocation with a PostScript installer
will install resource files into <code>/gs/Resource</code>.</p>
<h2><a name="PDF_scripting"></a>Scripting the PDF interpreter</h2>
<h3><a name="PS_functions"></a>PostScript functions</h3>
<p>We have not previously documented the internals of the Ghostscript PDF interpreter, but we have, on
occasion, provided solutions that rely upon scripting the interpreter from PostScript. This was
possible because the interpreter was written in PostScript.</p>
<p>From release 9.55.0 Ghostscript comes supplied with two PDF interpreters, the original written in PostScript
and a brand-new interpreter written in C. While the new interpreter can be run as part of the GhostPDL family
it has also been integrated into Ghostscript, and can be run from the PostScript environment in a similar fashion
to the old interpreter. We plan to deprecate, and eventually remove, the old interpreter and carry on with the new one.</p>
<p>Because we have supplied solutions in the past based on the old interpreter, we have had to implement
the same capabilities in the integration of the new interpreter. Since this has meant discovering which internal
portions were being used, working out how those function, and duplicating them anew, it seemed a good time to
document these officially, so that in future the functionality would be available to all.</p>
<p>The following functions existed in the original PDF interpreter and have been replicated for the new
interpreter. It should be possible to use these for the forseeable future.</p>
<dl>
<dt><code><file> runpdf - </code></dt>
<dd> Called from the modified PostScript run operator (which copies stdin to a temp
file if required). Checks for PDF collections, processes all requested pages.</dd>
<dt><code><file> runpdfbegin -</code></dt>
<dd> This must be called before performing any further operations. Its exact action depends on which
interpreter is being used, but it essentially sets up the environment to process the file as a PDF</dd>
<dt><code><int> pdfgetpage <pagedict> | <null></code></dt>
<dd> int is a number from 1 to N indicating the desired page number from
the PDF file. Returns the a dictionary containing various informational key/value pairs.
If this fails, returns a null object.</dd>
<dt><code> - pdfshowpage_init -</code></dt>
<dd> In the PostScript PDF interpreter this simply adds 1 to the /DSCPageCount value in a dictionary.
It has no effect in the new PDF interpreter but is maintained for backwards compatibility.</dd>
<dt><code><pagedict> pdfshowpage_setpage <pagedict></code></dt>
<dd> Takes a dictionary as returned from pdfgetpage, extracts various
parameters from it, and sets the media size for the page, taking into
account the boxes, and requested Box, Rotate value and PDFFitPage.</dd>
<dt><code><pagedict> pdfshowpage_finish -</code></dt>
<dd> Takes a dictionary as returned from pdfgetpage, renders the page content
executes showpage to transfer the rendered content to the device.</dd>
<dt><code>- runpdfend -</code></dt>
<dd> Terminates the PDF processing, executes restore and various cleanup activities.</dd>
<dt><code><file> pdfopen <dict></code></dt>
<dd> Open a PDF file and read the header, trailer
and cross-reference.</dd>
<dt><code><dict> pdfclose -</code></dt>
<dd> Terminates processing the original PDF file object. The dictionary parameter
should be the one returned from pdfopen</dd>
<dt><code><pagedict> pdfshowpage -</code></dt>
<dd> Takes a dictionary returned from pdfgetpage and calls the pdfshowpage_init
pdfshowpage_setpage, pdfshowpage_finish trio to start the page, set up the
media and render the page.</dd>
<dt><code><int> <int> dopdfpages -</code></dt>
<dd> The integers are the first and last pages to be run from the file. Runs a loop from
the fist integer to the last. NOTE! If the current dictionary contains a PDFPageList
array then we 'get' the entry from the array corresponding to the current loop
index, and use that to determine whether we should draw the page. Otherwise we
simply draw the page. Uses pdfshowpage to actually render the page.</dd>
<dt><code>- runpdfpagerange <int> <int></code></dt>
<dd> Processes the PostScript /FirstPage, /LastPage and /PageList parameters. These are used together to build an internal array
of page numbers to run, which is used by dopdfpages to actually process the pages if PageList is present,
and a FirstPage and LastPage value. Despite the name this function does not actually 'run' any pages at all.
<p>Normal operation simply calls runpdf with an opened-for-read PostScript file object. The table below shows the normal
calling sequence</p>
<blockquote><table>
<tr valign="bottom">
<th align="left">Function</th>
<th align="left">Calls</th>
<th align="left">Calls</th>
<th align="left">Calls</th></tr>
<tr valign="top">
<td>runpdf</td>
<td>runpdfbegin</td>
<td>pdfopen</td>
<td> </td></tr>
<tr valign="top">
<td> </td>
<td>process_trailer_attrs</td>
<td> </td>
<td> </td>
</tr>
<tr valign="top">
<td> </td>
<td>runpdfpagerange</td>
<td> </td>
<td> </td></tr>
<tr valign="top">
<td> </td>
<td>dopdfpages</td>
<td>pdfgetpage</td>
<td> </td></tr>
<tr valign="top">
<td> </td>
<td> </td>
<td>pdfshowpage</td>
<td>pdfshowpage_init</td></tr>
<tr valign="top">
<td> </td>
<td> </td>
<td> </td>
<td>pdfshowpage_setpage</td></tr>
<tr valign="top">
<td> </td>
<td> </td>
<td> </td>
<td>pdfshowpage_finish</td></tr>
<tr valign="top">
<td> </td>
<td>runpdfend</td>
<td>pdfclose</td>
<td> </td></tr>
</table></blockquote>
<p>It is important to get the number of spots and the presence of transparency correct when
rendering. Failure to do so will lead to odd output, and potentially crahses. This can be important in situations
such as N-up ordering.</p>
<p>As an example, if we have 2 A4 pages and want to render them side-by-side on A3 media, we might set up
the media size to A3, draw the first page contents, translate the origin, draw the second page contents
and then render the final content. If the first PDF page did not contain transparency, but the second did, it
would be necessary to set /PageHasTransparency before drawing the first PDF page.</p>
<h3><a name="PDF_PS_operators"></a>PostScript operators interfacing to the PDF interpreter</h3>
<p>The PostScript functions documented above must somehow interface with the actual PDF interpreter, and this is done
using a small number of custom PostScript operators. These operators do not exist in standard PostScript; they
are specific to the Ghostscript implementation. These operators are documented here for the benefit of any
developers wishing to use them directly.</p>
</dd>
<dt><code>dict .PDFInit <PDFContext></code></dt>
<dd> Initialises an instance of the PDF interpreter. dict is an optional dictionary that contains any interpreter-level
switches, such as PDFDEBUG, this is used to set the initial state of the PDF interpreter.
The return value is a PDFcontext object which is an opaque object to be used with the other PDF operators.</dd>
<dt><code>filename PDFcontext .PDFFile -</code></dt>
<dd> Opens a named file and associates it with the instance of the PDF interpreter.
Filename is a string containing a fully qualified path to the PDF file to open, this file must have been made accesible
by setting --permit-file-read.
</dd><dt><code>file PDFcontext .PDFStream -</code></dt>
<dd> Takes an already open (disk-based) file and associates it with the instance of the PDF interpreter.
</dd><dt><code>PDFcontext .PDFClose -</code></dt>
<dd> If the context contains an open PDF file which was opened via the .PDFfile operator, this closes the file.
Files associated with the context by the .PDFStream operator are unaffected. Regardless of the source it then shuts down the PDF interpreter and frees the associated memory.
</dd><dt><code>PDFcontext .PDFInfo dict</code></dt>
<dd> PDFcontext is a PDFcontext object returned from a previous call to .PDFInit.
The returned dictionary contains various key/value pairs with useful file level information:
<blockquote>
<code>/NumPages</code> int<br>
<code>/Creator</code> string<br>
<code>/Producer</code> string<br>
<code>/IsEncrypted</code> boolean<br>
</blockquote>
</dd><dt><code>PDFcontext .PDFMetadata -</code></dt>
<dd> PDFcontext is a PDFcontext object returned from a previous call to .PDFInit.
For the benefit of high level devices, this is a replacement for 'process_trailer_attrs' which is a seriously misnamed function now.
This function needs to write any required output intents, load and send Outlines to the device, copy the Author, Creator, Title, Subject
and Keywords from the Info dict to the output device, copy Optional Content Properties (OCProperties) to the output device.
If an AcroForm is present send all its fields and link widget annotations to fields, and finally copy the PageLabels. If we add support for anything else, it will be here too..
</dd><dt><code>PDFcontext int .PDFPageInfo -</code></dt>
<dd> The integer argument is the page number to retrieve information for.
Returns a dictionary with the following key/value pairs:
<blockquote>
<code>/UsesTransparency</code> true|false<br>
<code>/SpotColours</code> array of names, may be empty|<br>
<code>/MediaBox</code> [llx lly urx ury]<br>
<code>/HasAnnots</code> true|false<br>
<code>/FontsUsed</code> array of names, may be empty.<br>
</blockquote>
May also contain (if they are present in the Page dictionary)
<blockquote>
<code>/ArtBox</code> [llx lly urx ury]<br>
<code>/CropBox</code> [llx lly urx ury]<br>
<code>/BleedBox</code> [llx lly urx ury]<br>
<code>/TrimBox</code> [llx lly urx ury]<br>
<code>/UserUnit</code> int<br>
</blockquote>
</dd>
<dt><code>PDFcontext int .PDFDrawPage -</code></dt>
<dd> PDFcontext is a PDFcontext object returned from a previous call to .PDFInit.
The integer argument is the page number to be processed.
Interprets the page content stream(s) of the specified page using the current graphics state.
</dd>
<dt><code>PDFcontext int .PDFDrawAnnots -</code></dt>
<dd> PDFcontext is a PDFcontext object returned from a previous call to .PDFInit.
The integer argument is the page number to be processed.
Renders the Annotations (if any) of the specified page using the current graphics state
For correct results, the graphics state when this operator is run should be the same as when
PDFDrawPage is executed.
<p>Note: The PDFcontext object created by PDFInit must (clearly) have a PDF file associated
with it before you can usefully use it. Attempting to use a PDFcontext with
any of the processing operators (eg .PDFDrawPage) before using either .PDFStream of .PDFFile
to associate a file with the context will result in an error.
</p>
</dd>
</dl>
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<small>Copyright © 2000-2022 Artifex Software, Inc. All rights reserved.</small>
<p>
This software is provided AS-IS with no warranty, either express or
implied.
This software is distributed under license and may not be copied, modified
or distributed except as expressly authorized under the terms of that
license. Refer to licensing information at <a href="https://www.artifex.com">https://www.artifex.com</a>
or contact Artifex Software, Inc., 1305 Grant Avenue - Suite 200,
Novato, CA 94945, U.S.A., +1(415)492-9861, for further information.
<p>
<small>Ghostscript version 9.56.1, 4 April 2022
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