PostScript (PS)

A PostScript file is a program in the PostScript language. A printer or an interpreter such as Ghostscript runs the program, and the program draws text, vector graphics and images onto pages. Pages are described in points (1/72 inch) and print at the full resolution of the device.

PostScript is still used as a printer language and as the output of older Unix and TeX tools (dvips, groff, a2ps). For documents you want to view or share, PDF has replaced it: a PDF has the same imaging model but is a data structure, not a program, so a viewer can open any page directly.

When to use PostScript#

• Use when a printer, RIP or print workflow needs PostScript.
• Use when an old toolchain produces it (dvips, groff -Tps, a2ps, enscript); convert to PDF afterwards.
• Avoid for documents to share or archive: use PDF. Most current systems can’t open .ps without installing Ghostscript.
• Avoid opening files from untrusted sources without a sandbox: a PostScript file is a program and interpreters have had many security bugs.
• Avoid for a single graphic to place in another document: use EPS, SVG or PDF.

File structure#

A PostScript file is plain text (sometimes with binary image or font data) made of PostScript operators in postfix order: operands first, then the operator. Only the interpreter knows what the file draws. To let other programs process a file without running it, well-formed files follow the Document Structuring Conventions (DSC): special comments that start with %% and mark the header, the prolog and each page.

%!PS-Adobe-3.0
%%Creator: my program
%%Title: hello.ps
%%Pages: 1
%%BoundingBox: 0 0 612 792
%%DocumentMedia: Letter 612 792 0 () ()
%%LanguageLevel: 2
%%EndComments
%%BeginProlog
/F { findfont exch scalefont setfont } bind def
%%EndProlog
%%BeginSetup
%%EndSetup
%%Page: 1 1
24 /Helvetica F
72 720 moveto (Hello, PostScript) show
newpath 72 600 moveto 300 0 rlineto stroke
showpage
%%Trailer
%%EOF

The coordinate origin is the bottom-left corner of the page and the y axis goes up. 72 720 moveto is 1 inch from the left edge, 10 inches from the bottom. showpage outputs the current page.

DSC comments#

With DSC a tool can count pages, extract a page range or reorder pages (psselect, psnup from psutils) by copying text between %%Page: comments. A file that breaks the conventions (for example, a page that depends on state set by an earlier page) prints fine but breaks such tools.

Language levels#

Binary data such as images is usually written as ASCII85 or hex so the file stays 7-bit text.

Other things at the start of a file#

• Files printed to a file from Windows printer drivers often start with PJL commands (1B 25 2D 31 32 33 34 35 58, ESC%-12345X@PJL ...) before %!PS.
• An EPS file can start with a 30-byte binary header C5 D0 D3 C6 followed by the PostScript and a TIFF or WMF preview. See EPS.
• %!PS-Adobe-3.0 EPSF-3.0 marks a single-page Encapsulated PostScript file.

Converting PostScript#

Ghostscript does almost every conversion:

# PostScript to PDF
ps2pdf in.ps out.pdf
gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=out.pdf in.ps

# PostScript to PNG, one file per page, 150 dpi, anti-aliased
gs -dNOPAUSE -dBATCH -sDEVICE=png16m -r150 -dTextAlphaBits=4 -dGraphicsAlphaBits=4 \
   -sOutputFile=page-%03d.png in.ps

# extract text
gs -dNOPAUSE -dBATCH -sDEVICE=txtwrite -sOutputFile=out.txt in.ps

# PDF to PostScript
pdf2ps in.pdf out.ps

Since Ghostscript 9.50 -dSAFER is the default: the PostScript program can’t read or write arbitrary files. Keep it on for files you didn’t create.

Specifications and documentation#

• PostScript Language Reference, Third Edition (Adobe, PDF): the language, operators and imaging model
• Document Structuring Conventions Specification 3.0 (Adobe Technical Note 5001, PDF)
• Ghostscript documentation: command-line options, output devices, the C API
• Ghostscript output devices and vector devices (pdfwrite, ps2write, eps2write)
• PostScript on Wikipedia
• Document Structuring Conventions on Wikipedia

Software that opens PostScript files#

macOS Preview opened PostScript up to macOS 12. macOS 13 removed it from Preview and macOS 14 removed the built-in PostScript-to-PDF converter (pstopdf). On a current Mac, install Ghostscript (brew install ghostscript) and run ps2pdf.

Libraries#

Open-source libraries that interpret, render or write PostScript. See all PostScript libraries for a comparison.

Related formats#

• PDF: the successor, with the same imaging model in a structure that doesn’t need to be executed
• EPS: a single-page PostScript file with a bounding box, for placing into other documents
• DVI: TeX output, usually converted to PostScript with dvips or to PDF
• SVG: the vector graphics format for the web
• XPS: Microsoft’s fixed-layout format, used in the Windows print path