PostScript Language
Ghostscript’s capabilities in relation to PostScript
The Ghostscript interpreter, except as noted below, is intended to execute properly any source program written in the (LanguageLevel 3) PostScript language as defined in the PostScript Language Reference, Third Edition (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 PostScript Language Reference Manual (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 “status
” operator. The base interpreter may be configured (see the documentation on building Ghostscript for how to configure it) by adding any combination of the following:
The ability to process PostScript Type 1 fonts. This facility is normally included in the interpreter.
The CMYK color extensions listed in section A.1.4 of the Second Edition (including
colorimage
). These facilities are available only if thecolor
,dps
, orlevel2
feature was selected when Ghostscript was built.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 dps feature or the
level2
feature was selected when Ghostscript was built.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 compfont feature or the
level2
feature was selected when Ghostscript was built.The ability to load TrueType fonts and to handle PostScript Type 42 (encapsulated TrueType) fonts. These facilities are available only if the
ttfont
feature was selected when Ghostscript was built.The PostScript Level 2 “filter” facilities except the
DCTEncode
andDCTDecode
filters. These facilities are available only if thefilter
,dps
, orlevel2
feature was selected when Ghostscript was built.The PostScript Level 2
DCTEncode
andDCTDecode
filters. These facilities are available only if thedct
orlevel2
feature was selected when Ghostscript was built.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
level2
feature was selected when Ghostscript was built.All PostScript LanguageLevel 3 operators and facilities listed in the Third Edition, except as noted below. These facilities are available only if the
psl3
feature was selected when Ghostscript was built.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
epsf
feature was selected when Ghostscript was built.
Ghostscript currently does not implement the following PostScript LanguageLevel 3 facilities:
Settable
ProcessColorModel
for page devices, except for a very few special devices.IODevices
other than%stdin
,%stdout
,%stderr
,%lineedit
,%statementedit
,%os%
, and (if configured)%pipe%
and%disk0%
through%disk0%
.
Ghostscript can also interpret files in the Portable Document Format (PDF) 1.7 format defined in the PDF Reference Version 1.7, distributed by Adobe Systems Incorporated, except as noted below. This facility can be disabled by deselecting the pdf feature when Ghostscript is built.
Ghostscript currently implements the majority of non-interactive features defined in the PDF reference.
Ghostscript also includes a number of additional operators defined below that are not in the PostScript language defined by Adobe.
Implementation limits
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.
Architectural limits
Architectural limits (corresponds to Adobe table B.1)
Quantity |
Limit |
Type |
Adobe |
---|---|---|---|
integer |
32-bit |
twos complement integer |
|
real |
single-precision |
IEEE float |
|
array |
16777216 |
elements |
65535 |
dictionary |
16777215 |
elements |
65535 |
string |
16777216 |
characters |
65535 |
name |
16383 |
characters |
127 |
filename |
128 * |
characters |
|
|
none |
(capacity of memory) |
15 |
|
none |
(capacity of memory) |
13 |
* 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.
Typical memory limits in LanguageLevel 1
Memory limits (corresponds to Adobe table B.2)
Quantity |
Limit |
Type |
Adobe |
---|---|---|---|
|
200 |
||
|
100 |
||
operand stack |
800 |
500 |
|
dictionary stack |
20 |
||
execution stack |
250 |
||
interpreter level |
none |
(capacity of memory) |
10 |
path |
none |
(capacity of memory) |
1500 |
dash |
11 |
||
VM |
none |
(capacity of memory) |
240000 |
file |
none |
(determined by operating system) |
6 |
image |
65535 |
values (samples × components) for 1-, 2-, 4-, or 8-bit samples |
3300 |
32767 |
values for 12-bit samples |
3300 |
Other differences in VM consumption
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.
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.
The garbage collector doesn’t reclaim portions of arrays obtained with getinterval, rather it collects entire arrays.
Additional operators in Ghostscript
Graphics and text operators
Transparency
Note
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 SAFER is in force (as it is by default from version 9.50 onwards). To utilise these operators you will either have to disable SAFER
(-dNOSAFER
) or use the command line parameter -dALLOWPSTRANSPARENCY
. The latter will make the custom operators available, but leave the file access controls active.
Ghostscript provides a set of operators for implementing the transparency and compositing facilities of PDF 1.4. These are defined only if the transpar
option was selected when Ghostscript was built. We do not attempt to explain the underlying graphics model here: for details, see Adobe Technical Note #5407, “Transparency in PDF”. 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.
What follows is a subset of all the custom operators related to transparency, but covers the most useful, most common requirements.
Graphics state operators
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 showpage
. Any marking operations made after the compositor is popped will bypass the transparent imaging model, and may produce unexpected output.
<depth> .pushpdf14devicefilter -
Installs the transparency compositor device into the graphics state. At present the
depth
parameter should always be zero (Subject To Change.)- .popdf14devicefilter -
Removes (or, more accuracately, disables) the transparency compositor in graphics state.
<modename> .setblendmode -
Sets the blending mode in the graphics state. If the mode name is not recognized, causes a
rangecheck
error. The initial value of the blending mode is/Compatible
.- .currentblendmode <modename>
Returns the graphics state blend mode on the stack.
[Deprecated as of 9.53] <0..1> .setopacityalpha -
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.
[Deprecated as of 9.53] - .currentopacityalpha <0..1>
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.
[Deprecated as of 9.53] <0..1> .setshapealpha -
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.
[Deprecated as of 9.53] - .currentshapealpha <0..1>
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.
<0..1> .setstrokeconstantalpha -
Sets the stroke alpha value in the graphics state. The initial stroke alpha value is 1.
- .currentstrokeconstantalpha <0..1>
Returns the graphics state stroke alpha value on the stack.
<0..1> .setfillconstantalpha -
Sets the fill alpha value in the graphics state. The initial fill alpha value is 1.
- .currentfillconstantalpha <0..1>
Returns the graphics state fill alpha value on the stack.
<bool> .setalphaisshape -
If true, the values set by
setstrokeconstantalpha
andsetfillconstantalpha
are interpreted as shape values. The initial value of the AIS flag is false.- .currentalphaisshape <0..1>
Returns the graphics state alpha is shape (AIS) on the stack.
<bool> .settextknockout -
Sets the text knockout flag in the graphics state. The initial value of the text knockout flag is true.
- .currenttextknockout <bool>
Returns the graphics state text knockout on the stack.
Rendering stack operators
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.
Beginning and ending groups must nest properly with respect to save and restore: save and restore do not save and restore the layer stack. Currently, layers are not required to nest with respect to gsave and grestore, 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.
Warning
THIS AREA IS SUBJECT TO CHANGE.
<paramdict> <llx> <lly> <urx> <ury> .begintransparencygroup -
Begins a new transparency group. The
ll/ur
coordinates are the bounding box of the group in the current user coordinate system.paramdict
has the following keys:/Isolated
(optional) Boolean; default value = false.
/Knockout
(optional) Boolean; default value = false.
- .endtransparencygroup -
Ends the current transparency group, compositing the group being ended onto the group that now becomes current.
<cs_set?> <paramdict> <llx> <lly> <urx> <ury> .begintransparencymaskgroup -
Begins a new transparency mask, which is represented as a group. The
ll/ur
coordinates are the bounding box of the mask in the current user coordinate system.paramdict
has the following keys:/Subtype
(required) Name, either
/Alpha
or/Luminosity
./Background
(optional) Array of number.
/TransferFunction
(optional) Function object (produced by applying
.buildfunction
to a Function dictionary).
The
cs_set
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 true, and the intended color space set in the graphics state prior to the.begintransparencymaskgroup
call.<mask#> .endtransparencymask -
Ends the current transparency mask group, compositing the mask group being ended and setting it as the current soft mask in the graphics state. The
mask#
parameter indicates whether the mask should be treated as as opacity mask (0
) or shape (1
).
New ImageType
The transparency extension defines a new ImageType 103, similar to ImageType 3 with the following differences:
The required
MaskDict
is replaced by two optional dictionaries,OpacityMaskDict
andShapeMaskDict
. If present, these dictionaries must have aBitsPerComponent
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.A
Matte
entry may be present in one or both mask dictionaries, indicating premultiplication of the data values. If bothMaskDicts
have aMatte
entry and the values of the twoMatte
entries are different, arangecheck
error occurs.InterleaveType
appears in theMaskDicts
, not theDataDict
, because each mask has its ownInterleaveType
.InterleaveType
2 (interlaced scan lines) is not supported.
Other graphics state operators
<int> .setoverprintmode -
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
DeviceCMYK
, 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.- .currentoverprintmode <int>
Returns the current overprint mode.
Character operators
<font> <charcode> %Type1BuildChar -
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
...show
,stringwidth
, orcharpath
), it looks up the nameBuildChar
in the font dictionary to find a procedure to run. If it does not find this name, and if theFontType
is 1, the interpreter instead uses the value (looked up on the dictionary stack in the usual way) of the name%Type1BuildChar
.The standard definition of
%Type1BuildChar
is in the initialization filegs_type1.ps
. Users should not need to redefine%Type1BuildChar
, except perhaps for tracing or debugging.<font> <charname> %Type1BuildGlyph -
Provides the Type 1 implementation of
BuildGlyph
.
Other operators
Mathematical operators
<number> arccos <number>
Computes the arc cosine of a number between -1 and 1.
<number> arcsin <number>
Computes the arc sine of a number between -1 and 1.
Dictionary operators
mark <key1> <value1> <key2> <value2> ... .dicttomark <dict>
Creates and returns a dictionary with the given keys and values. This is the same as the PostScript Level 2 >> operator, but is available even in Level 1 configurations.
<dict> <key> .knownget <value> true
,<dict> <key> .knownget false
Combines
known
andget
in the obvious way.
File operators
<file> .fileposition <integer> true
Returns the position of file. Unlike the standard
fileposition
operator, which causes an error if the file is not positionable,.fileposition
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.<string> findlibfile <foundstring> <file> true
,<string> findlibfile <string> false
Opens the file of the given name for reading, searching through directories as described in the usage documentation. If the search fails,
findlibfile
simply pushes false on the stack and returns, rather than causing an error.
<prefix_string|null> <access_string> .tempfile <string> <file>
Creates and opens a temporary file like the file operator, also returning the file name. There are three cases for the
<prefix_string|null>
operand:null
: 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/tmp/gs_a1234
.A string that contains only alphanumeric characters, underline, and dash: create the file in the standard temporary directory, but use the
<prefix_string>
as the first part of the file name. E.g., if<prefix_string>
isxx
, the temporary file might be named/tmp/xxa1234
.A string that is the beginning of an absolute file name: use the
<prefix_string>
as the first part of the file name. E.g., if<prefix_string>
is/my/tmpdir/zz
, the temporary file might be named/my/tmpdir/zza1234
.
When running in
SAFER
mode, the absolute path must be one of the strings on the permit file writing list (see -dSAFER) .
Ghostscript also supports the following IODevice
in addition to a subset of those defined in the Adobe documentation:
%pipe%command
, which opens a pipe on the given command. This is supported only on operating systems that provide popen (primarily Unix systems, and not all of those).%disk#%
, 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 thediskn.dev
feature is specified during the build.This feature is intended to allow compatibility with font downloaders that expect to store fonts on the
%disk
device of the printer.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:mark /Root (directory_specification) (%disk#) .putdevparams
For example, to store the files of the
%disk0
device on the directory/tmp/disk0
, use:mark /Root (/tmp/disk0/) (%disk0) .putdevparams
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.
Miscellaneous operators
<array> bind <array>
Depending on the command line parameters
bind
is redefined as:
Flag
Definition
DELAYBIND
Returns the argument, stores the argument for later use by
.bindnow
<array> .bind <array>
Performs standard bind operation as defined in PLRM regardless of the
DELAYBIND
flag.
- .bindnow -
Applies
bind
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 frombind
is discarded.Since v. 8.12
.bindnow
undefines itself and restores standard definition ofbind
operator. In earlier versions after calling.bindnow
, the postscriptbind
operator needs to be rebound to the internal implementation.bind
, as in this fragment from theps2ascii
script:DELAYBIND { .bindnow /bind /.bind load def } if
This is necessary for correct behavior with later code that uses the
bind
operator.<string> getenv <string> true
,<string> getenv false
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.
<string> <boolean> .setdebug -
Sets or clears any subset of the debugging flags included in
<string>
based on the value of<boolean>
. These correspond to the debug flags set by-Z
on the command line and enable debug and tracing output from various internal modules.Note
Most tracing output is only produced if the Ghostscript interpreter was built with the
DEBUG
preprocessor symbol defined.The
zsetdebug()
C function, which implements this operator, is a useful breakpoint for debuggers. Inserting ‘() true .setdebug
’ in the interpreted code will trigger a breakpoint at that location without side effects. The current flag state is available in C as thegs_debug[]
array, indexed by character value. Thezsetdebug
function will be entered, andgs_debug[]
updated, whether or not Ghostscript is built with theDEBUG
preprocessor symbol defined, so this is useful even with release builds.- .setsafe -
If Ghostscript is started with
-dNOSAFER
or-dDELAYSAFER
, this operator can be used to enterSAFER
mode (see -dSAFER)The following is deprecated, see -dSAFER.
Since
SAFER
mode is implemented with userparameters and device parameters, it is possible to usesave
andrestore
before and after.setsafe
to return toNOSAFER
mode, but note that such a save object is accessible to any procedures or file run inSAFER
mode. A malicious file with an unbalanced restore could potentially restore back to a point whereSAFER
was not in operation.Note
This uses
setpagedevice
to change.LockSafetyParams
, so the page will be erased as a side effect of this operator.- .locksafe -
The following is deprecated, see -dSAFER.
This operator sets the current device’s
.LockSafetyParams
and theLockFilePermissions
user parameter true as well as adding the paths onLIBPATH
andFONTPATH
and the paths given by the system params/GenericResourceDir
and/FontResourceDir
to the currentPermitFileReading
list of paths.If Ghostscript is started with
-dNOSAFER
or-dDELAYSAFER
, this operator can be used to enterSAFER
mode with the current set ofPermitFile...
user parameters in effect. Since.setsafe
sets thePermitFile...
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 enterSAFER
mode.For example, to enable reading everywhere, but disallow writing and file control (deleting and renaming files), the following can be used:
{ << /PermitFileReading [ (*) ] /PermitFileWriting [ ] /PermitFileControl [ ] >> setuserparams .locksafe } stopped pop
In the above example, use of stopped will allow the use of this sequence on older versions of Ghostscript where
.locksafe
was not an operator.Note
This uses
setpagedevice
to change.LockSafetyParams
, so the page will be erased as a side effect of this operator.See also .LockSafetyParams and User Parameters.
<name> <string> .addcontrolpath
Adds a single path to the file access control lists.
The
<name>
parameter can be one of:
/PermitFileReading
/PermitFileWriting
/PermitFileControl
Whilst the string parameter is the path to be added to the requested list.
Note
Any attempt to call this operator after
.activatepathcontrol
has been called will result in aFatal
error, and the interpreter will immediately exit.
.activatepathcontrol
Activates file access controls. Once activated, these access controls remain in place until the interpreter shuts down.
.currentpathcontrolstate
Returns true on the operand stack if file access control has been activated, false if not.
<dict> .genordered <dict> (default: /OutputType /Type3).
,<dict> .genordered <string> (/OutputType /ThreshString).
,<dict> .genordered <array> (/OutputType /TOSArray).
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
sethalftone
or as a component Halftone of aHalftoneType 5
Halftone dictionary. The/OutputType
parameter can also select other than Halftone Type 3 as the return paramter,<dict>
has the following keys (all are optional):/Frequency
Integer; default value = 75
/Angle
Integer; default value = 0
/HResolution
Real or Integer; default value is device X resolution.
/VResolution
Real or Integer; default value is device Y resolution.
/DotShape
Integer; default value = 0 (CIRCLE). Other shapes available are:
1=REDBOOK, 2=INVERTED, 3=RHOMBOID, 4=LINE_X, 5=LINE_Y, 6=DIAMOND1, 7=DIAMOND2, 8=ROUNDSPOT
/SuperCellSize
Integer; default value = 1 – actual cell size determined by Frequency, Angle, H/V Resolution.
A larger value will allow more levels to be attained.
/Levels
Integer; default value = 1 – actual number of gray levels is determined by Frequency and H/V Resolution.
SuperCellSize may need to be specified large enough to achieve the requested number of gray levels.
/OutputType
Name; default value = /Type3 (HalftoneType 3 dictionary).
/ThreshString
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)./TOSArray
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.
.shellarguments
This operator is used to access the
ARGUMENTS
command line option.Relies on Ghostscript being called with the “
--
” command line option - see Input Control.See examples in
lib
for more information.
Device operators
<matrix> <width> <height> <palette> makeimagedevice <device>
Makes a new device that accumulates an image in memory.
matrix
is the initial transformation matrix: it must be orthogonal (that is, [a 0 0 b x y] or [0 a b 0 x y]). palette is a string of 2^N or 3 × 2^N elements, specifying how the 2^N 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 <ff 00>; 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<000000 0000ff 00ff00 00ffff ff0000 ff00ff ffff00 ffffff>
. 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. This operator is only available when running Ghostscript with NOSAFER.Alternatively,
palette
can be 16, 24, 32, or null (equivalent to 24). These are interpreted as:Palette
Bits allocated per color
16
5 red, 6 green, 5 blue
24
8 red, 8 green, 8 blue
32
8C, 8M, 8Y, 8K
Note
One can also make an image device (with the same palette as an existing image device) by copying a device using the copydevice operator.
<device> <index> <string> copyscanlines <substring>
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 image 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.
<device> setdevice -
Sets the current device to the specified device. Also resets the transformation and clipping path to the initial values for the device. Signals an
invalidaccess
error if the device is a prototype or if .LockSafetyParams is true for the current device.Some device properties may need to be set before
setdevice
is called. For example, the pdfwrite device will try to open its output file, causing anundefinedfilename
error ifOutputFile
hasn’t been set to a valid filename. In such cases use the level 2 operator instead:<< /OutputDevice /pdfwrite /OutputFile (MyPDF.pdf) >> setpagedevice
.- currentdevice <device>
Gets the current device from the graphics state.
Filters
Standard filters
In its usual configuration, Ghostscript supports all the standard PostScript LanguageLevel 3 filters, both encoding and decoding, except that it does not currently support:
the
EarlyChange
key in theLZWEncode
filter.
Ghostscript also supports additional keys in the optional dictionary operands for some filters. For the LZWDecode
filter:
InitialCodeLength <integer> (default 8)
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.
FirstBitLowOrder <boolean> (default false)
If true, codes appear with their low-order bit first.
BlockData <boolean> (default false)
If true, the data is broken into blocks in the manner specified for the GIF file format.
For the CCITTFaxEncode
and CCITTFaxDecode
filters:
DecodedByteAlign <integer> (default 1)
An integer N with the value 1, 2, 4, 8, or 16, specifying that decoded data scan lines are always a multiple of N bytes. The encoding filter skips data in each scan line from Columns to the next multiple of N bytes; the decoding filter pads each scan line to a multiple of N bytes.
Non-standard filters
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.
<target> /BCPEncode filter <file>
,<source> /BCPDecode filter <file>
Create filters that implement the Adobe Binary Communications Protocol. See Adobe documentation for details.
<target> <seed_integer> /eexecEncode filter <file>
Creates a filter for encrypting data into the encrypted format described in the Adobe Type 1 Font Format documentation. The
seed_integer
must be 55665 for theeexec
section of a font, or 4330 for aCharString
. Note that for theeexec
section of a font, this filter produces binary output and does not include the initial 4 (or lenIV) garbage bytes.<source> <seed_integer> /eexecDecode filter <file>
,<source> <dict> /eexecDecode filter <file>
Creates a filter for decrypting data encrypted as described in the Adobe Type 1 Font Format documentation. The
seed_integer
must be 55665 or 4330 as described just above. PDF interpreters don’t skip space characters after operatoreexec
. Usekeep_spaces = true
for decoding embedded PDF fonts. Recognized dictionary keys are:seed <16-bit integer> (required) lenIV <non-negative integer> (default=4) eexec <bool> (default=false) keep_spaces <bool> (default=false)
<target> /MD5Encode filter <file>
Creates a filter that produces the 16-byte MD5 digest of the input. Note that no output is produced until the filter is closed.
<source> <hex_boolean> /PFBDecode filter <file>
Creates a filter that decodes data in
.PFB
format, the usual semi-binary representation for Type 1 font files on IBM PC and compatible systems. Ifhex_boolean
is true, binary packets are converted to hex; if false, binary packets are not converted.<target> <dict> /PixelDifferenceEncode filter <file>
,<source> <dict> /PixelDifferenceDecode filter <file>
Implements the Predictor=2 pixel-differencing option of the LZW filters. Recognized keys are:
Colors <integer> (1 to 4, default=1) BitsPerComponent <integer> (1, 2, 4, or 8, default=8) Columns <integer> (>= 0, required)
See the Adobe PDF Reference Manual for details.
<target> <dict> /PNGPredictorEncode filter <file>
,<source> <dict> /PNGPredictorDecode filter <file>
Implements the “filter” algorithms of the Portable Network Graphics (PNG) graphics format. Recognized keys are:
Key
Range
Default
Colors <integer>
1 to 16
16
BitsPerComponent <integer>
1, 2, 4, 8, or 16
8
Columns <integer>
>= 0
1
Predictor <integer>
10 to 15
15
The
Predictor
is the PNG algorithm number + 10 for theEncoding
filter; theDecoding
filter ignoresPredictor
. 15 means the encoder attempts to optimize the choice of algorithm. For more details see the PNG specification.<target> /TBCPEncode filter <file>
,<source> /TBCPDecode filter <file>
Create filters that implement the Adobe Tagged Binary Communications Protocol. See Adobe documentation for details.
<target> /zlibEncode filter <file>
,<source> /zlibDecode filter <file>
Creates filters that use the data compression method variously known as ‘zlib’ (the name of a popular library that implements it), ‘Deflate’ (as in RFC 1951, 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
Flate
filters are actually a combination of this filter with an optional predictor filter.
Unstable filters
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.
<target/source> <string> ByteTranslateEncode/Decode filter <file>
string
must be a string of exactly 256 bytes. Creates a filter that converts each input byteb
tostring[b]
. Note that theEncode
andDecode
filters operate identically: the client must provide a string for theDecode
filter that is the inverse mapping of thestring
for theEncode
filter.<target/source> <dict> BoundedHuffmanEncode/Decode filter <file>
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:
FirstBitLowOrder <bool> (default=false) MaxCodeLength <int> (default=16) EndOfData <bool> (default=true) EncodeZeroRuns <int> (default=256) Tables <int_array>
<target/source> <dict> BWBlockSortEncode/Decode filter <file>
This filter implements the Burroughs-Wheeler block sorting compression method, which we’ve heard is also used in the popular
bzip2
compression application. The only recognized dictionary key is:BlockSize <integer> (default=16384)
Device parameters
Ghostscript supports the concept of device parameters for all devices, not just page devices. Here are the currently defined parameters for all devices:
.LockSafetyParams <boolean>
This parameter allows for improved system security by preventing PostScript programs from being able to change potentially dangerous device parameters such as
OutputFile
. This parameter cannot be set false if it is already true.If this parameter is true for the current device, attempt to set a new device that has
.LockSafetyParams
false will signal aninvalidaccess
error.BitsPerPixel <integer> (usually read-only)
Number of bits per pixel.
.HWMargins [<four floats>]
Size of non-imageable regions around the edges of the page, in points (units of 1/72in; see the notes on measurements in the documentation on devices).
HWSize [<integer> <integer>]
X and Y size in pixels.
%MediaSource <integer>
The input tray key as determined by
setpagedevice
. PostScript language programs don’t set this parameter directly; they can request a particular tray through theMediaPosition
setpagedevice
parameter, but thesetpagedevice
logic need not necessarily honor the request. Devices which support switchable trays should implement%MediaSource
in theirput_params
device procedure, but (unlike most other such parameters) need not implement corresponding reading logic inget_params
.%MediaDestination <integer>
The output tray key as determined by
setpagedevice
. Handling by devices should be parallel to%MediaSource
..IgnoreNumCopies <boolean>
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 ignoreNumCopies
regardless because of limitation of the output format or the implementation.Name <string> (read-only)
The device name. Currently the same as
OutputDevice
.Colors, GrayValues, RedValues, GreenValues, BlueValues, ColorValues (usually read-only)
As for the
deviceinfo
operator of Display PostScript.Red
,Green
,Blue
, andColorValues
are only defined ifColors > 1
.TextAlphaBits, GraphicsAlphaBits (usually read-only)
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.
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.
Ghostscript also supports the following read-only parameter that is not a true device parameter:
.EmbedFontObjects <integer>
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.)
In addition, the following are defined per Adobe’s documentation for the setpagedevice
operator:
Duplex (if supported)
HWResolution
ImagingBBox
Margins
LeadingEdge
MediaPosition
NumCopies (for printers only)
Orientation (if supported)
OutputDevice
PageOffset (write-only)
PageSize
ProcessColorModel (usually read-only)
Some devices may only allow certain values for HWResolution
and PageSize
. The null device ignores attempts to set PageSize
; its size is always [0 0]
.
It should be noted that calling setpagedevice
with one of the above keys may reset the effects of any pdfmark
commands up to that point. In particular this is true of HWResolution
, a behavior that differs from Adobe Distiller.
For raster printers and image format (jpeg*, tiff*, png* …) devices these page device parameters are also defined:
MaxBitmap <integer>
Maximum space for a full page raster image (bitmap) in memory. This value includes the space for padding raster lines and for an array of pointers for each raster line, thus the
MaxBitmap
value to allow a givenPageSize
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.BandListStorage <file|memory>
The default is determined by the make file macro
BAND_LIST_STORAGE
. Since memory is always included, specifying-sBandListStorage=memory
when the default is file 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.BufferSpace <integer>
Size of the buffer space for band lists, if the full page raster image (bitmap) is larger than
MaxBitmap
(see above.)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.If
MaxBitmap
(above) forces banding mode, and ifBufferSpace
is large enough, the display list (clist
) will consist of a single band.The
BufferSpace
will determine the size of the ‘consolidation’ buffer (above) even if the MaxBitmap value is low enough to force banding/clist mode.BGPrint <boolean>
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, false, causes the rendering and printing to be done in the same thread as the parser. When-dBGPrint=true
, the page output will be overlapped with parsing and writing theclist
for the next page.If the device does not support background printing, rendering and printing will be performed as if
-dBGPrint=false
.Note
The background printing thread will allocate a band buffer (size determined by the
BufferSpace
orBandBufferSpace
values) in addition to the band buffer in the ‘main’ parsing thread.If
NumRenderingThreads
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 thatBGPrint
is disabled for vector devices such as pdfwrite andNumRenderingThreads
has no effect on these devices either.GrayDetection <boolean>
When true, and when the display list (
clist
) banding mode is being used, during writing of theclist
, the color processing logic collects information about the colors used before the device color profile is applied. This allows special devices that examinedev->icc_struct->pageneutralcolor
with the information that all colors on the page are near neutral, i.e. monochrome, and converting the rendered raster to gray may be used to reduce the use of color toners/inks.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 (
DEV_NEUTRAL
andAB_NEUTRAL
inbase/gscms.h
) to allow colors close to neutral to be detected as neutral. Changing this value requires rebuilding.Among the devices distributed with the source, currently only the
pnmcmyk
device supports this parameter and will produce either aP7 PAM CMYK
output or aP5 PGM Gray
output depending on the use of color on the page.Also, the
pageneutralcolor
status can be interrogated as a device parameter of the same name. Using PostScript there are several methods:currentpagedevice /pageneutralcolor get
mark currentdevice getdeviceprops .dicttomark /pageneutralcolor get
/pageneutralcolor /GetDeviceParam .special_op { exch pop }{ //false } ifelse
Note that the
pageneutralcolor
state is reset to false after the page is output, so this parameter is only valid immediately beforeshowpage
is executed, although thesetpagedevice
EndPage
procedure can be used to check the state just prior to the actual output of the page that resetspagenuetralcolor
. For example:<< /EndPage { exch pop 2 ne dup { currentpagedevice /pageneutralcolor get (pageneutralcolor: ) print = flush } if } >> setpagedevice
Note
Since
-dGrayDetection=true
requires extra checking during writing of theclist
, this option should only be used for devices that support the optimization of pages to monochrome, otherwise performance may be degraded for no benefit.Since
GrayDetection=true
is only effective when inclist
(banding) mode, it is recommended to also force banding. For example:-dGrayDetection=true -dMaxBitmap=0
.NumRenderingThreads <integer>
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.NumRenderingThreads
of 1 or higher results in bands rendering in the specified number of ‘background’ threads.The number of threads should generally be set to the number of available processor cores for best throughput.
Note that each thread will allocate a band buffer (size determined by the
BufferSpace
orBandBufferSpace
values) in addition to the band buffer in the ‘main’ thread.Additionally note that this parameter has no effect with devices which do not generally render to a bitmap output, such as the vector devices (e.g. pdfwrite) and has no effect when rendering, but not using a
clist
. See Improving performance.OutputFile <string>
An empty string means “send to printer directly”, otherwise specifies the file name for output;
%d
is replaced by the page number for page-oriented output devices; on Unix systems%pipe%
command writes to a pipe. (|
command also writes to a pipe, but is now deprecated). Also see the-o
parameter.Attempts to set this parameter if
.LockSafetyParams
is true will signal aninvalidaccess
error.OpenOutputFile <boolean>
If true, open the device’s output file when the device is opened, rather than waiting until the first page is ready to print.
PageCount <integer> (read-only)
Counts the number of pages printed on the device.
The following parameters are for use only by very specialized applications that separate band construction from band rasterization. Improper use may cause unpredictable errors. In particular, if you only want to allocate more memory for banding, to increase band size and improve performance, use the BufferSpace
parameter, not BandBufferSpace
.
BandHeight <integer>
The height of bands when banding. 0 means use the largest band height that will fit within the
BandBufferSpace
(orBufferSpace
, ifBandBufferSpace
is not specified). IfBandHeight
is larger than the number of lines that will fit in the buffer, opening the device will fail. If the value is -1, theBandHeight
will automatically be set to the page height (1 band for the entire page). This is primarily for developers debuggingclist
issues.BandWidth <integer>
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.BandBufferSpace <integer>
The size of the band buffer in the rasterizing pass, in bytes. 0 means use the same buffer size as for the interpretation pass.
Ghostscript supports the following parameter for setpagedevice
and currentpagedevice
that is not a device parameter per se:
ViewerPreProcess <procedure>
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
.
User parameters
Ghostscript supports the following non-standard user parameters:
ProcessDSCComment <procedure|null>
If not null, this procedure is called whenever the scanner detects a DSC comment (comment beginning with
%%
or%!
). There are two operands, the file and the comment (minus any terminatingEOL
), which the procedure must consume.ProcessComment <procedure|null>
If not null, this procedure is called whenever the scanner detects a comment (or, if
ProcessDSCComment
is also not null, a comment other than aDSC
comment). The operands are the same as forProcessDSCComment
.LockFilePermissions <boolean>
If true, this parameter and the three
PermitFile...
parameters cannot be changed. Attempts to change any of the values whenLockFilePermissions
is true will signalinvalidaccess
. Also, when this value is true, the file operator will giveinvalidaccess
when attempting to open files (processes) using the%pipe
device.Also when
LockFilePermissions
is true, strings cannot reference the parent directory (platform specific). For example (../../xyz
) is illegal on unix, Windows and Macintosh, and ([.#.#.XYZ]
) is illegal on VMS.This parameter is set true by the
.setsafe
and.locksafe
operators.PermitFileReading <array of strings>
,PermitFileWriting <array of strings>
,PermitFileControl <array of strings>
These parameters specify paths where file reading, writing and the ‘control’ operations are permitted, respectively. File control operations are
deletefile
andrenamefile
. Forrenamefile
, the filename for the current filename must match one of the paths on thePermitFileControl
list, and the new filename must be on both thePermitFileControl
and thePermitFileWriting
lists of paths.The strings can contain wildcard characters as for the
filenameforall
operator and unless specifying a single file, will end with a*
for directories (folders) to allow access to all files and sub-directories in that directory.Note
The strings are used for
stringmatch
operations similar tofilenameforall
, 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).The SAFER mode and the
.setsafe
operator set all three lists to empty arrays, thus the only files that can be read are the%stdin
device and onLIBPATH
orFONTPATH
or theResource
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 .tempfile operator).AlignToPixels <integer>
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
TextAlphaBits
. If the latter is 1, the same rendering results regardless of the value ofAlignToPixels
. The initial value defaults to 1, but this may be overridden by the command line argument-dAlignToPixels
.
GridFitTT <integer>
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.
This parameter controls the hinting of Truetype glyphs.
A value of 0 disables grid fitting for all True Type fonts (not generally recommended).
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.
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.
With Freetype, a value of 3 is effectively equivalent to 1.
This parameter defaults to 1, but this may be overridden on the command line with
-dGridFitTT=n
.
Miscellaneous additions
Extended semantics of ‘run’
The operator run 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.
Decoding resources
Decoding
is a Ghostscript-specific resource category. It contains various resources for emulating PostScript fonts with other font technologies. Instances of the Decoding
category are tables which map PostScript glyph names to character codes used with TrueType, Intellifont, Microtype and other font formats.
Currently Ghostscript is capable of PostScript font emulation in 2 ways :
Through FAPI plugins.
With TrueType font files, using the native font renderer, by specifying TrueType font names or files in
Resource/Init/Fontmap.GS
.
Decoding
resources are not currently used by the native font renderer.
An instance of the Decoding
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, /Unicode
/Decoding
resource maps to Unicode UTF-16.
The rules for using Decoding
resources in particular cases are specified in the configuration file Resource/Init/xlatmap
. See the file itself for more information.
The file format for Decoding
resource files is generic PostScript. Users may want to define custom Decoding
resources. The ParseDecoding
procset
defined in Resource/Init/gs_ciddc.ps
allows representation of the table in a comfortable form.
CIDDecoding resources
CIDDecoding
resources are similar to Decoding
resources, except they map Character Identifiers (CIDs)
rather than glyph names. Another difference is that the native Ghostscript font renderer uses CIDDecoding
resources while emulate CID
fonts with TrueType or OpenType fonts.
An instance of the CIDDecoding
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.
The dictionary includes the additional key CIDCount
. Its value is the maximal CID
defined, plus one.
The Ghostscript library is capable of generating some CIDDecoding
instances automatically, using the appropriate CMap
(character map) resources. This covers most of practical cases if the neccessary CMap
resources are provided. See the table .CMapChooser
in Resource/Init/gs_ciddc.ps
for the names of automatically generated resources and associated CMaps
. 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.
The file format for CIDDecoding
resource file is generic PostScript. Users may want to define custom resources to CIDDecoding
resource category.
GlyphNames2Unicode
GlyphNames2Unicode
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 FontInfo
dictionary under the key GlyphNames2Unicode
. Ghostscript recognises it and uses to generate ToUnicode CMaps
with pdfwrite.
Multiple Resource directories
Since 8.10 release Ghostscript maintains multiple resource directories.
Ghostscript does not distinguish lib
and Resource
directories. There is no file name conflicts because lib
does not contain subdirectories, but Resource
always store files in subdirectories.
The search method with multiple resource directories appears not fully conforming to PLRM. We cannot unconditionally call ResourceFileName
while executing findresource
or resourcestatus
, resourceforall
, because per PLRM it always returns a single path. Therefore Ghostscript implements an extended search method in findresource
, resourcestatus
and resourceforall
, which first calls ResourceFileName
and checks whether the returned path points to an existing file. If yes, the file is used, otherwise Ghostscript searches all directories specified in LIB_PATH
. With a single resource directory it appears conforming to PLRM and equivalent to Adobe implementations.
ResourceFileName
may be used for obtaining a path where a resource file to be installed. In this case Ghostscript to be invoked with -sGenericResourceDir=path
, specifying an absolute path. The default value for GenericResourceDir
is a relative path. Therefore a default invocation with a PostScript installer will install resource files into /gs/Resource
.
Scripting the PDF interpreter
PostScript functions
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.
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.
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.
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.
<file> runpdf -
Called from the modified PostScript run operator (which copies
stdin
to a temp file if required). Checks for PDF collections, processes all requested pages.<file> runpdfbegin -
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.
<int> pdfgetpage <pagedict> | <null>
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.- pdfshowpage_init -
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.<pagedict> pdfshowpage_setpage <pagedict>
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 requestedBox
,Rotate
value andPDFFitPage
.<pagedict> pdfshowpage_finish -
Takes a dictionary as returned from
pdfgetpage
, renders the page content executesshowpage
to transfer the rendered content to the device.- runpdfend -
Terminates the PDF processing, executes restore and various cleanup activities.
<file> pdfopen <dict>
Open a PDF file and read the header, trailer and cross-reference.
<dict> pdfclose -
Terminates processing the original PDF file object. The dictionary parameter should be the one returned from
pdfopen
.<pagedict> pdfshowpage -
Takes a dictionary returned from
pdfgetpage
and calls thepdfshowpage_init
,pdfshowpage_setpage
,pdfshowpage_finish
trio to start the page, set up the media and render the page.<int> <int> dopdfpages -
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 the two values on the stack are ignored and we use the range triples from that array (even/odd, start, end) to determine the pages to process. Page numbers for start and end are1..lastpage
and even/odd is 1 for odd, 2 for even, otherwise 0. Usespdfshowpage
to actually render the page.- runpdfpagerange <int> <int>
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 bydopdfpages
to actually process the pages ifPageList
is present, and aFirstPage
andLastPage
value.Despite the name this function does not actually ‘run’ any pages at all.
Normal operation simply calls
runpdf
with an opened-for-read PostScript file object. The table below shows the normal calling sequence:Function
Calls
Calls
Calls
runpdf
runpdfbegin
pdfopen
process_trailer_attrs
runpdfpagerange
dopdfpages
pdfgetpage
pdfshowpage
pdfshowpage_init
pdfshowpage_setpage
pdfshowpage_finish
runpdfend
pdfclose
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.
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.
PostScript operators interfacing to the PDF interpreter
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.
dict .PDFInit <PDFContext>
Initialises an instance of the PDF interpreter.
dict
is an optional dictionary that contains any interpreter-level switches, such asPDFDEBUG
, this is used to set the initial state of the PDF interpreter. The return value is aPDFContext
object which is an opaque object to be used with the other PDF operators.filename PDFContext .PDFFile -
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
.file PDFContext .PDFStream -
Takes an already open (disk-based) file and associates it with the instance of the PDF interpreter.
PDFcontext .PDFClose -
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.PDFContext .PDFInfo dict
PDFContext
is aPDFContext
object returned from a previous call to.PDFInit
. The returned dictionary contains various key/value pairs with useful file level information:/NumPages int /Creator string /Producer string /IsEncrypted boolean
PDFContext .PDFMetadata -
PDFContext
is aPDFContext
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 sendOutlines
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 thePageLabels
. If we add support for anything else, it will be here too.PDFContext int .PDFPageInfo -
The integer argument is the page number to retrieve information for. This value starts from zero for the first page. Returns a dictionary with the following key/value pairs:
/UsesTransparency true|false /NumSpots integer containing the number of spot inks on this page /MediaBox [llx lly urx ury] /HasAnnots true|false
May also contain (if they are present in the Page dictionary):
/ArtBox [llx lly urx ury] /CropBox [llx lly urx ury] /BleedBox [llx lly urx ury] /TrimBox [llx lly urx ury] /UserUnit int /Rotate number
PDFcontext int .PDFPageInfoExt -
As per
.PDFPageInfo
above but returns ‘Extended’ information. This consists of two additional arrays in the returned dictionary:/Spots array of names, may be empty /Fonts array of dictionaries, one dictionary per font used on the page.
Each font dictionary contains:
/BaseFont string containing the name of the font. /Subtype string containing the type of the font, as per the PDF Reference. /ObjectNum if present, the object number of the font in the file (fonts may be defined inline and have no object number). /Embedded boolean indicating if the font's FontDescriptor includes a FontFile and is therefore embedded.
Type 0 fonts also contain:
/Descendants an array containing a single font dictionary, contents as above.
PDFContext int .PDFDrawPage -
PDFContext
is aPDFContext
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.PDFContext int .PDFDrawAnnots -
PDFContext
is aPDFContext
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.
Note
The
PDFContext
object created byPDFInit
must (clearly) have a PDF file associated with it before you can usefully use it. Attempting to use aPDFContext
with any of the processing operators (e.g..PDFDrawPage
) before using either.PDFStream
of.PDFFile
to associate a file with the context will result in an error.
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