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 the color, dps, or
level2 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 and DCTDecode filters. These
facilities are available only if the filter,
dps, or level2 feature was selected when
Ghostscript was built.
The PostScript Level 2 DCTEncode and
DCTDecode filters. These facilities are available only if
the dct or level2 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:
Native Separation and DeviceN color
spaces -- the alternate space is always used.
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)
1.3 format defined in the Portable
Document Format Reference Manual Version 1.3 of March 11, 1999,
distributed by Adobe Systems
Incorporated, except as noted below. This facility is available only if
the pdf feature was selected when Ghostscript was built.
Ghostscript currently does not implement the following PDF 1.3 facilities:
Native Separation and DeviceN color
spaces, as noted above for PostScript.
Native ICCBased color spaces -- these too always use the
alternate space.
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
65535
elements
dictionary
65534
elements
65535
string
65535
characters
name
16383
characters
127
filename
128*
characters
save level
none
(capacity of memory)
15
gsave level
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
userdict
200
FontDirectory
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) for1-, 2-, 4-, or 8-bit samples
3300
32767
values for 12-bit samples
3300
Other differences in VM consumption
Packed array elements occupy either 2 bytes or 8 bytes. The average
element size is probably about 5 bytes. Names occupy 12 bytes plus the
space for the string.
Additional operators in Ghostscript
Graphics and text operators
Transparency
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 PDF Specification version 1.4 or later. Note,
however, that Ghostscript's model generalizes that of PDF 1.4 in that Ghostscript
maintains separate alpha and mask values for opacity and shape, rather than
a single value with a Boolean that says whether it represents opacity or
shape. EVERYTHING IN THIS SECTION IS SUBJECT TO CHANGE.
Graphics state
operators
<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 current blending mode.
<0..1> .setopacityalpha -
Sets the opacity alpha value in the graphics state.
The initial opacity alpha value is 1.
- .currentopacityalpha <0..1>
Returns the current opacity alpha value.
<0..1> .setshapealpha -
Sets the shape alpha value in the graphics state.
The initial shape alpha value is 1.
- .currentshapealpha <0..1>
Returns the current shape alpha value.
<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 current text knockout flag.
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 layers 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. THIS AREA IS SUBJECT TO CHANGE.
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.
- .discardtransparencygroup -
Ends and discards the current transparency group.
- .endtransparencygroup -
Ends the current transparency group, compositing the group being ended
onto the group that now becomes current.
Begins a new transparency mask. 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).
- .discardtransparencymask -
Ends and discards the current transparency mask.
<masknum> .endtransparencymask -
Ends the current transparency mask, installing it as the current opacity
(masknum = 0) or shape (masknum = 1) mask in
the graphics state.
<masknum> .inittransparencymask -
Resets the current opacity (masknum = 0) or shape
(masknum = 1) mask to an infinite mask with alpha = 1
everywhere.
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 and
ShapeMaskDict. If present, these dictionaries must have a
BitsPerComponent 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 both
MaskDicts have a Matte entry and the values
of the two Matte entries are different, a
rangecheck error occurs.
InterleaveType appears in the MaskDicts,
not the DataDict, because each mask has its own
InterleaveType. InterleaveType 2
(interlaced scan lines) is not supported.
Other graphics state operators
<bool> .setaccuratecurves -
Sets a graphics state flag that determines whether curves and arcs,
when flattened, always start and end with a line that is a segment of the
tangent; this also causes butt and square caps to be properly perpendicular
to the tangent. initgraphics sets this flag to false, to
match other PostScript implementations.
- .currentaccuratecurves <bool>
Returns the current value of the accurate curves flag.
<int> .setcurvejoin -
Sets a graphics state parameter that determines how to treat the joins
between the line segments produced when a curve is flattened. The parameter
value may be either -1 or a value acceptable to setlinejoin.
If the parameter value is -1, the join used for flattened curve line
segments is given by the current line join parameter in the graphics state
(except that if the line join value is "none", a bevel join is used), which
matches the Adobe Red Book, but not the Adobe implementations; if the curve
join parameter value is a line join value, that type of join is used for
flattened curve line segments, regardless of the value of the graphics state
line join parameter. The initial (and default) value of the curve join
parameter is 2, causing bevel joins to be used: this matches the Adobe
implementations. initgraphics sets the parameter to its
default value.
- .currentcurvejoin <int>
Returns the current value of the curve join parameter.
<bool> .setdashadapt -
Sets a graphics state flag that determines whether dash patterns do
(true) or do not (false) automatically scale themselves so that each line
segment consists of an integral number of pattern repetitions.
initgraphics sets this flag to false.
- .currentdashadapt <bool>
Returns the current value of the dash adaptation flag.
<matrix> .setdefaultmatrix -
Sets the default matrix that is returned by
defaultmatrix and installed by initmatrix.
Ordinary programs should not use this operator.
<num> <bool> .setdotlength -
Sets a graphics state parameter that determines the handling of
zero-length lines (dots). If the dot length is zero, dots are painted as
circles if round line caps are in effect, otherwise they are not painted at
all. If the dot length is non-zero, dots are treated exactly like lines of
the given length: the length is specified in user coordinates (like line
width) if bool is false, or in default user coordinates of
points (units of 1/72in; see the notes
on measurements in the documentation on devices) if
bool is true. Dots occurring as part of dash patterns will
be oriented correctly; isolated dots will be oriented as though they were
part of a vertical line. initgraphics sets the dot length
to zero.
- .currentdotlength <num> <bool>
Returns the current dot length and dot length mode.
<dx> <dy> .setfilladjust2 -
Sets graphics state parameters that cause all filled and stroked
regions to be "fattened" by the given amount relative to an algorithm that
only paints pixels whose centers fall within the region to be painted.
dx and dy are numbers between 0 and 0.5,
measured in device space. The only two values that are likely to be useful
are 0, which gives a pure center-of-pixel rule, and 0.5, which gives
Adobe's any-part-of-pixel rule. (0.5 is treated slightly specially in
order to create half-open pixels per Adobe's specification.)
- .currentfilladjust2 <dx> <dy>
Returns the current fill adjustment values.
<bool> .setlimitclamp -
Sets a graphics state flag that determines whether attempts to set the
current point outside the internally representable range should clamp the
value to the largest representable value (true) or give a
limitcheck error (false). initgraphics sets
this flag to false, to match other PostScript implementations.
- .currentlimitclamp <bool>
Returns the current value of the limit clamp flag.
<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.
Path operators
- .dashpath -
If there is no current dash pattern, does nothing. Otherwise, does the
equivalent of flattenpath and then chops up the path as
determined by the dash pattern.
<x> <y> <width> <height> .rectappend -
<numarray> .rectappend -
<numstring> .rectappend -
Appends a rectangle or rectangles to the current path, in the same
manner as rectfill, rectclip, etc. Defined
only if the dps or level2 option was
selected when Ghostscript was built.
Painting operators
Ghostscript supports an experimental extension of the PostScript imaging
model to include RasterOp and some related facilities.
This extension is available only if the rasterop option was
selected when building Ghostscript.
With the RasterOp extension, imaging operations compute a
function D = f(D,S,T) in RGB space, where f is an
arbitrary 3-input Boolean function, D is the destination (frame
buffer or print buffer), S is the source (described below), and
T is the texture (the current PostScript color, which may be a
pattern). The source and texture depend on the PostScript imaging
operation:
For fill and stroke, the source is
solid black, covering the region to be painted; the texture is the current
PostScript color.
For show and imagemask, the source is
solid black, covering the pixels to be painted; the texture is the current
PostScript color.
For image and colorimage, the source is
the image data; the texture depends on an optional Boolean parameter,
CombineWithColor, in the image dictionary. If
CombineWithColor is false (the default), the texture is
solid black. If CombineWithColor is true, the texture is
the current color. For the non-dictionary form of the image operator,
CombineWithColor is considered to be false.
The rasterop option adds the following operators:
<int8> .setrasterop -
Sets the RasterOp function in the graphics state. The
default function is 252, Source | Texture.
- .currentrasterop <int8>
Returns the current RasterOp function.
<bool> .setsourcetransparent -
Sets source transparency in the graphics state. When source
transparency is true, white source pixels prevent storing into the
destination, regardless of what the RasterOp function
returns. The default source transparency is false.
- .currentsourcetransparent <bool> -
Returns the current source transparency.
<bool> .settexturetransparent -
Sets texture transparency in the graphics state. When texture
transparency is true, white texture pixels prevent storing into the
destination, regardless of what the RasterOp function
returns. The default texture transparency is false.
- .currenttexturetransparent <bool> -
Returns the current texture transparency.
For more information on RasterOp and transparency, please consult chapter 5
of the "PCL 5 Color Technical Reference Manual",
Hewlett-Packard
Manual Part No. 5961-0635.
Character operators
<string> <bool> .charboxpath -
For each character C in the rendering of <string>, let the
bounding box of Cin device space be the four
user-space points p1x/y, p2x/y, p3x/y, and p4x/y. For each
character in order, .charboxpath appends the following to
the current path:
This creates a path whose pathbbox is the
bbox of the string.
If <bool> is false, the equivalent of:
p1x p1y moveto
p3x p3y lineto
If the CTM is well-behaved (consists only of reflection, scaling, and
rotation by multiples of 90 degrees), this too creates a (simpler) path
whose pathbbox is the bbox of the string.
Does all the work for rendering a Type 1 outline. This operator, like
setcharwidth and setcachedevice, is valid
only in the context of a show operator -- that is, it must only be called
from within a BuildChar or BuildGlyph
procedure.
<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, or
charpath), it looks up the name BuildChar
in the font dictionary to find a procedure to run. If it does not find
this name, and if the FontType 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 file gs_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> <value> .forceput -
Equivalent to put, but works even if
dict is not writable, and (if dict is
systemdict or the current save level is 0) even if
dict is in global VM and key and/or
value is in local VM. This operator should be used
only initialization code, and only in executeonly procedures: it must not be
accessible after initialization.
<dict> <key> .forceundef -
Equivalent to undef, but works even if
dict is not writable. This operator should be used
only initialization code, and only in executeonly procedures: it must not be
accessible after initialization.
<dict> <key> .knownget <value> true
<dict> <key> .knownget false
Combines known and get in the
obvious way.
<dict> <integer> .setmaxlength -
Sets the capacity (maxlength) of a dictionary.
Causes a dictfull error if the dictionary has more
occupied entries than the requested capacity.
String and name operators
<integer> .bytestring <bytestring>
Allocates and returns a bytestring, a special data type that can be
larger than the maximum size of a string (64K-1 bytes) and can be used in
place of a string with a very few operators.
<name> .namestring <string>
Returns the (read-only) string for a name.
<string> <charstring> .stringbreak <index|null>
Searches for a character in string that appears
somewhere in charstring. If such a character is found,
returns the index of the first such character; if no such character is
found, returns null.
<obj> <pattern> .stringmatch <bool>
Matches obj against a pattern in which '*' matches 0 or
more characters and '?' matches any single character. If
obj is a string or a name, matches its characters against
the pattern; if obj is of any other type, the result is
true if the pattern is the single character "*" and
false otherwise.
Encrypts fromString according to the algorithm for
Adobe Type 1 fonts, writing the result into toString.
toString must be at least as long as
fromString, or a rangecheck error occurs.
state is the initial state of the encryption algorithm (a
16-bit non-negative integer); newState is the new state of
the algorithm.
Decrypts fromString according to the algorithm for
Adobe Type 1 fonts, writing the result into toString.
Other specifications are as for type1encrypt.
Relational operators
<number|string> <number|string> max <number|string>
Returns the larger of two numbers or strings.
<number|string> <number|string> min <number|string>
Returns the smaller of two numbers or strings.
File operators
<file> .filename <string> true
<file> .filename false
If the file was opened by the file or
.tempfile operator, returns the file name and
true; if the file is a filter, returns
false.
<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.
Reads bytes from a file like readstring, but also leaves
the bytes in the file buffer so they will be read again by a subsequent read
operation. Currently gives a rangecheck error if
string is larger than the file's buffer.
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> is xx, 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 list given by the PermitFileWriting
userparameter. Temporary files created with .tempfile can
be deleted when in SAFER mode, and can be renamed to one of the paths
that is on both the PermitFileControl and PermitFileWriting
paths.
<file> <integer> .unread -
Pushes back the last-read character onto the front of the file. If the
file is open only for writing, or if the integer argument is not the same
as the last character read from the file, causes an ioerror
error. May also cause an ioerror if the last operation on
the file was not a reading operation. This operator is now deprecated:
use .peekstring in new code.
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 the
diskn.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.
Virtual memory operators
<save> .forgetsave -
Cancels the effect of a save, making it as though the save never
happened.
Miscellaneous operators
<array> bind <array>
Depending on the command line parameters bind is redefined as:
Flag
Definition
NOBIND
/bind {} def ;
no operation, returns the argument
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
NOBIND or DELAYBIND flags.
- .bindnow -
Applies bind operator to all savad procedures after binding has been
deferred through -dDELAYBIND. Note that idiom recognition has no effect for the deferred
binding because the value returned from bind is discarded.
Since v. 8.12 .bindnow undefines itself and restores standard definition of
bind operator. In earlier versions after calling .bindnow,
the postscript bind operator needs to be rebound to the internal implementation
.bind, as in this fragment from the ps2ascii script:
DELAYBIND {
.bindnow
/bind /.bind load def
} if
This is necessary for correct behavior with later code that uses the bind operator.
<obj1> <obj2> ... <objn> <n> .execn ...
This executes obj1 through objn in that
order, essentially equivalent to
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.
<name> <array> .makeoperator <operator>
Constructs and returns a new operator that is actually the given
procedure in disguise. The name is only used for printing. The operator
has the executable attribute.
Operators defined in this way do one other thing besides running the
procedure: if an error occurs during the execution of the procedure, and
there has been no net reduction in operand or dictionary stack depth, the
operand or dictionary stack pointer respectively is reset to its position
at the beginning of the procedure.
<string> <boolean> .setdebug -
If the Ghostscript interpreter was built with the DEBUG
flag set, sets or resets any subset of the debugging flags normally
controlled by -Z in the command line. Has no effect
otherwise.
- .oserrno <errno>
Returns the error code for the most recent operating system error.
- .oserrorstring <string>
Returns the error string for the most recent operating system error.
<array> <procedure> .runandhide ... <array>
Runs the <procedure> after removing the
<array> from the stack. As long as <array>
is not contained in any readable dictionaries or elsewhere on stacks, it
will not be accessible to <procedure>.
This operator is intended to allow hiding a <save> object
during execution of procedures or files that run in SAFER mode.
If a save is performed prior to entering SAFER mode
with .setsafe, using the save object as the operand to
restore will return to NOSAFER mode. In order to
prevent the procedures running in SAFER mode from being able to
return to NOSAFER mode, this operator should be used.
Upon return from the file or procedure restore can be used
to return to NOSAFER mode.
Note: The array operand hidden during the execution of the file or
procedure will be placed at the top of the operand stack which may be on
top of objects that the file or procedure leaves on top of the stack.
Thus removing objects below the array may be needed to prevent an
invalidrestore error.
For example, in order for a script or job server to execute a file
somefile.ps with the SAFER mode restrictions in place, returning
to unrestricted NOSAFER mode when the procedure exits is as follows:
Start Ghostscript with -dNOSAFER
... % perform any device set up w/o restrictions
[ save ] % create a save object before SAFER
(somefile.ps) (r) file cvx % open the file to process
.setsafe % enter SAFER mode
.runandhide % run the file hiding the save object
count 1 roll % place array below anything left over
count 1 sub { pop } repeat % pop left over stuff
cleardictstack % prevent invalidrestore from dicts
0 get restore % go back to NOSAFER mode
Another refinement on the above would be to execute .runandhide
using stopped in order to report errors but continue processing.
- .setsafe -
If Ghostscript is started with -dNOSAFER or
-dDELAYSAFER, this operator can be used to enter SAFER
mode (see -dSAFER)
Since SAFER mode is implemented with userparameters and device parameters,
it is possible to use save and restore before
and after .setsafe to return to NOSAFER mode, but care
should be taken to ensure that the save object is not
accessible to any procedures or file run in SAFER mode (see
.runandhide above).
Note: This uses setpagedevice to change .LockSafetyParams, so the page
will be erased as a side effect of this operator
- .locksafe -
This operator sets the current device's .LockSafetyParams
and the LockFilePermissions 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.
If Ghostscript is started with -dNOSAFER or
-dDELAYSAFER, this operator can be used to enter SAFER
mode with the current set of PermitFile... user parameters
in effect. Since .setsafe sets the PermitFile...
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 SAFER mode.
For example, to enable reading everywhere, but disallow writing and file
control (deleting and renaming files), the following can be used:
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.
<devicename> finddevice <device>
Creates a default instance of a device specified by name. The instance
is created in global VM. If finddevice is called more than
once with the same device name, it creates the default instance the first
time, and returns the same instance thereafter.
<devicename> findprotodevice <device>
Finds the prototype of a device specified by name. A prototype can be
used with .getdeviceparams or other parameter-reading
operators, but it is read-only and cannot be set with
setdevice: it must be copied first.
Reads a rectangle of rendered bits back from a device. This is only
guaranteed to be implemented for image devices (see below).
alpha? is 0 for no alpha, -1 for alpha first, 1 for alpha
last. std_depth is null for native pixels, number of bits
per component for a standard color space.
<index> .getdevice <device>
Returns a device from the set of devices known to the system. The
first device, which is the default, is numbered 0. If the
index is out of range, causes a rangecheck
error. This device is actually a prototype, not a directly usable device,
and is marked read-only; it cannot have its parameters changed or be
installed as the current 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.
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 that one can also make an image device (with the same palette as an
existing image device) by copying a device using the
copydevice operator.
Makes an image device as described above. word? is a
Boolean value indicating whether the data should be stored in a
word-oriented format internally. No ordinary PostScript programs should
use this operator.
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 with putdeviceprops before
setdevice is called. For example, the pdfwrite device will try
to open its output file, causing an undefinedfilename error if
OutputFile hasn't been set to a valid filename. Another method in such
cases is to use the level 2 operator instead:
<< /OutputDevice /pdfwrite /OutputFile (MyPDF.pdf) >> setpagedevice.
Sets properties of a device. May cause undefined,
invalidaccess, typecheck, rangecheck, or
limitcheck errors.
- flushpage -
On displays, flushes any buffered output, so that it is guaranteed to
show up on the screen; on printers, has no effect.
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 the LZWEncode
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.
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 the eexec
section of a font, or 4330 for a CharString. Note that for
the eexec section of a font, this filter produces binary
output and does not include the initial 4 (or lenIV) garbage
bytes.
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. Recognized dictionary keys are:
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. If hex_boolean is true, binary packets
are converted to hex; if false, binary packets are not converted.
The Predictor is the PNG algorithm number + 10 for the
Encoding filter; the Decoding filter
ignores Predictor. 15 means the encoder attempts to
optimize the choice of algorithm. For more details see the PNG
specification
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.
string must be a string of exactly 256 bytes. Creates a
filter that converts each input byte b to
string[b]. Note that the Encode
and Decode filters operate identically: the client must
provide a string for the Decode filter that
is the inverse mapping of the string for the
Encode filter.
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:
This filter implements the Burroughs-Wheeler block sorting compression
method, which we've heard is also used in the popular bzip2
compression application. See http://sources.redhat.com/bzip2/
for more information. The only recognized dictionary key is:
The Encode filter starts by initializing an internal
256-byte array a to the values 0 .. 255. This array will
always hold a permutation of these values. Then for each input byte
b, the filter outputs the index i such that
a[i] = b, and moves that element to the
front (element 0) of a, moving elements 0 .. i-1 to
positions 1 .. i. The Decode filter inverts this
process.
Device parameters
Ghostscript supports the concept of device parameters for all devices, not
just page devices. (For non-page devices, these are accessible through
getdeviceprops and putdeviceprops, as
indicated above.) 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 paramters 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 an
invalidaccess 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.
Name <string> (read-only)
The device name. Currently the same as OutputDevice.
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.
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:
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 printers these are also defined:
BufferSpace <integer>
Buffer space for band lists, if the bitmap is too big to fit in memory.
MaxBitmap <integer>
Maximum space for a full bitmap in memory.
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.)
Attempts to set this parameter if .LockSafetyParams is true
will signal an invalidaccess 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 (or BufferSpace, if
BandBufferSpace is not specified).
BandWidth <integer>
The width of bands in the rasterizing pass, in pixels. 0 means use the
actual page width.
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 terminating
EOL), 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 a DSC comment). The operands are the same as for
ProcessDSCComment.
LockFilePermissions <boolean>
If true, this parameter and the three PermitFile...
parameters cannot be changed. Attempts to change any of the values
when LockFilePermissions is true will signal invalidaccess.
Also, when this value is true, the file operator
will give invalidaccess 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 and renamefile.
For renamefile, the filename for the current filename
must match one of the paths on the PermitFileControl list, and the
new filename must be on both the PermitFileControl and the
PermitFileWriting 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
to filenameforall, 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
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
.tempfile operator).
Note: Limiting file reading as above is NOT compatible with
SAFER mode in release versions before 7.11 and corresponds to the use of
-dPARANOIDSAFER in version 7.04 (up to and not including
version 7.10) and GPL versions 6.53 (up to and not including 6.60).
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 of
AlignToPixels. 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 implements a reduced True Type bytecode interpreter,
which can interpret the subset of True Type glyph instructions
not covered by Apple's patents. This allows the Dynalab fonts to
rasterize properly.
Fonts with patented instructions can't be properly grid fitted.
This parameter controls the action of the reduced interpreter:
a value of 0 disables grid fitting for all fonts;
a value of 1 enables the grid fitting for glyphs that don't involve
patented instructions.
When set to 1 a warning is printed to stderr when a patented
instruction is encountered, and the glyph is rendered ignoring the
entire grid fitting program. This parameter defaults to 0, but this
may be overridden on the command line with
-dGridFitTT=1.
The bytecode interpreter is based in part of the work of the
Freetype Team.
UseWTS <boolean>
If true, and if AccurateScreens are specified (either as
a user parameter, or as a type 1 halftone dictionary parameter), then
the Well Tempered Screening algorithm is used for
halftoning. Otherwise, a rational tangent algorithm is chosen, which
will typically result in significant differences between the screen
angle and ruling requested, and actually rendered. Currently, the
performance of WTS is reasonably good when rendering to a full page
buffer, but not optimized for banded mode. Thus, when using WTS,
disable banding (setting
-dMaxBitmap=500000000 should work). In a future
version, WTS will be optimized for banded mode, and
UseWTS will be true by default.
Note: Currently, UseWTS can only be set using
the PostScript user parameters mechanism, not on the command line with
a -d switch. Use this code to enable it:
<< /UseWTS true >> setuserparams
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 :
2. With TrueType font files, using the native font renderer, by
specifying TrueType font names or files in lib/Fontmap.
Decoding resources are not current 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 character codes. 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
lib/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
lib/gs_ciddc.ps allows representation
of the table in a comfortable form.
CIDDecoding resources
CIDDecoding resources are similar to Decoding
resources, except they map Charaacter Identifiers (CIDs) rather than glyph names.
Another difference is that the native Ghostscript font renderer already uses
CIDDecoding resources while emulate CID fonts with TrueType.
An instance of the CIDDecoding resource category is
a dictionary of strings. Keys in the dictionary are integers,
which correspond to high order byte of a CID. Values are
512-bytes strings. Each string represents 256 character codes,
corresponding various values of the lower byte of CID.
Each character code ocupies 2 bytes, high order byte first.
Two zero bytes represent mapping to the default character.
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
lib/gs_ciddc.ps
for the names of automatically gerenated 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,
othervise 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.
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 the license contained in the file LICENSE in this distribution.
For more information about licensing, please refer to
http://www.ghostscript.com/licensing/. For information on
commercial licensing, go to http://www.artifex.com/licensing/ or
contact Artifex Software, Inc., 101 Lucas Valley Road #110,
San Rafael, CA 94903, U.S.A., +1(415)492-9861.