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.

	<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..4 (default=1)
			BitsPerComponent <integer> 1,2,4,8 (default=8)
			Columns <integer> >= 0 (required)
		  See the Adobe "Portable Document Format Reference Manual"
		  for details.

	<target> <dict> /PNGPredictorEncode filter <file>
	<source> <dict> /PNGPredictorDecode filter <file>
		Implements the "filter" algorithms of the PNG graphics
		  format.  Recognized keys are:
			Colors <integer> 1..16 (default=1)
			BitsPerComponent <integer> 1,2,4,8,16 (default=8)
			Columns <integer> >= 0 (default=1)
			Predictor <integer> 10..15 (default=15)
		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 libpng.mak, which has
		  a pointer to 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> /zlibEncode filter <file>
		Creates filters that use the zlib data compression method
		  (the same method used by the gzip application).
		  This filter is only available if the fzlib feature was
		  selected when Ghostscript was compiled and linked.

Various versions of Ghostscript may also support other non-standard filters
for experimental purposes.  The current version includes the following
non-standard filters, which are not documented further.  No guarantee is
made that these filters will exist in compatible form, or at all, in future
versions.

	<target/source> <string> ByteTranslateEncode/Decode
	<target> <int> BigStringEncode
	<target/source> <dict> BoundedHuffmanEncode/Decode
		FirstBitLowOrder <bool> false
		MaxCodeLength <int> 16
		EndOfData <bool> true
		EncodeZeroRuns <int> 256
		Tables <int_array>
	<target/source> <dict> BWBlockSortEncode/Decode
		BlockSize <int> 16384
	<target/source> MoveToFrontEncode/Decode

Ghostscript also supports additional keys in the optional dictionary
operands for some filters.  For the LZWDecode filter:

	InitialCodeLength <integer>
		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.
Default value: 8.

	FirstBitLowOrder <boolean>
		If true, codes appear with their low-order bit first.
Default value: false.

	BlockData <boolean>
		If true, the data is broken into blocks in the manner
specified for the GIF file format.  Default value: false.

For the CCITTFaxEncode and CCITTFaxDecode filters:

	DecodedByteAlign <integer>
		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.
Default value: 1.

Virtual memory operators
------------------------

	<save> .forgetsave -
		Cancels the effect of a save -- makes it as though the
		  save never happened.

Miscellaneous operators
-----------------------

	<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.

	<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.

	<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 OS error.

	- .oserror <string>
		Returns the error string for the most recent OS error.

Device operators
----------------

	<device> copydevice <device>
		Copies a device.  The copy is writable and installable.

	<index> .getdevice <device>
		Returns a device from the set of devices known to the
		  system.  The first device, which is 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.

	<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 (i.e., [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:
			16 = 5R, 6G, 5B bits;
			24 = 8R, 8G, 8B bits;
			32 = 8C, 8M, 8Y, 8K bits.
		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.

	<matrix> <width> <height> <palette> <word?> makewordimagedevice
	    <device>
		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.

	<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.  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.

	- currentdevice <device>
		Gets the current device from the graphics state.

	<device> getdeviceprops <mark> <name1> <value1> ... <namen> <valuen>
		Gets all the properties of a device.  Currently defined
		  names and values for all devices are:
			BitsPerPixel <integer>
				Usually read-only.  Number of bits per pixel.
			.HWMargins [<4 floats>]
				Size of non-imageable regions around edges
				  of page, in 1/72" units.
			HWSize [<integer> <integer>]
				X and Y size in pixels.
			Name <string>
				Read-only.  The device name.
				  Currently, same as OutputDevice.
			Colors, GrayValues, RedValues, GreenValues,
			  BlueValues, ColorValues
				As for the 'deviceinfo' operator of
				  Display PostScript.
			TextAlphaBits, GraphicsAlphaBits
				The number of bits of anti-aliasing
				  information for text or graphics
				  respectively.  Legal values are 1 (no
				  anti-aliasing), 2, or 4; the default value
				  for most devices is 1.  Read-only for
				  almost all devices.
		In addition, the following are defined per Adobe's
		  documentation for the setpagedevice operator:
			Duplex (if supported)
			HWResolution
			ImagingBBox
			Margins
			NumCopies (for printers only)
			Orientation (if supported)
			OutputDevice
			PageOffset (write-only)
			PageSize
			ProcessColorModel
		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].
		Red/Green/Blue/ColorValues are only defined if Colors > 1.
		For printers, the following are also defined:
			BufferSpace <integer>
				Buffer space for band lists, if the bitmap
				  is too big to fit in RAM.
			MaxBitmap <integer>
				Maximum space for a full bitmap in RAM.
			OutputFile <string>
				() means send to printer directly,
				  otherwise specifies the file name for
				  output; a %d is replaced by the page #;
				  on Unix systems, (|command) writes to a pipe
			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.

	<mark> <name1> <value1> ... <namen> <valuen> <device>
	    putdeviceprops <device>
		Sets properties of a device.  May cause undefined,
		  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.

Ghostscript supports the following page device parameters in addition to the
ones documented by Adobe and the ones described under getdeviceprops above:

	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.

Character operators
-------------------

	<string> <bool> .charboxpath -
		For each character C in the rendering of <string>, let the
		  bounding box of C *in 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:
			- If <bool> is true, the equivalent of:
				p1x p1y moveto
				p2x p2y lineto
				p3x p3y lineto
				p4x p4y lineto
				closepath
			- If <bool> is false, the equivalent of:
				p1x p1y moveto
				p3x p3y lineto
		  In either case, this creates a path whose pathbbox is the
		  bbox of the string.

	<font> <charname|charcode> <charname> <charstring> .type1execchar -
		Does all the work for rendering a Type 1 outline.  This
		  operator, like setcharwidth and setcachedevice, is
		  only valid in the context of a show operator -- i.e.,
		  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 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.

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PostScript is a trademark of Adobe Systems, Incorporated.