Encapsulated PostScript (EPS) File Format, Version 3.x

The Encapsulated PostScript File Format, usually abbreviated as EPS and sometimes as EPSF, was developed in the late 1980s by Adobe Systems Incorporated to facilitate the incorporation of illustrations into textual documents for printing. An EPS file employs Adobe's PostScript language to represent a single rectangular graphic. As stated in the PostScript Language Reference Manual, "An encapsulated PostScript (EPS) file is a PostScript program describing at most a single page in a form that can be imported by other applications to embed within a containing document." The EPS format is particularly suited to vector graphics or to graphics that combine vector graphics with raster data, sometimes referred to as "metafiles." For such images it is still widely used in scientific publications in 2017; vector graphics are often recommended because they are scalable. It has also been used for raster images, usually using the TIFF format, to be embedded in articles, but since raster images are not inherently scalable, and most publication processes now provide direct support for raster formats such as TIFF, PNG, or JPEG, this usage is now less common. In many contexts, EPS has been superseded by PDF.

EPS is a proprietary but publicly documented format. The format specification was originally published by Adobe in the late 1980s; version 3 was first released in 1990 and published as a separate document in 1992. The specification uses EPSF as the acronym for the format, but describes files conforming to the specification as EPS files. This description uses EPS in both contexts, as more consistent with later usage. The EPS format uses a primarily textual file based on Adobe's PostScript language, defined in the PostScript Language Reference Manual; an EPS file is also expected to comply with the PostScript Language Document Structuring Conventions Specification (DSC), which provides conventions for using PostScript comments to convey document characteristics and printing instructions. An EPS file is constrained to represent a single rectangular area. Although the primary purpose of an EPS file is for an illustration to be included in other pages, it is also used for layouts of complete pages. EPS has been considered a good choice of format for vector graphic illustrations intended for high-resolution or large-scale printing and commonly used for printing to PostScript printers and imagesetters. EPS files are typically created and edited in illustration programs such as Adobe Illustrator or CorelDRAW. As vector graphics, EPS files have been particularly useful for illustrations intended for use at different scales, such as logos and advertisements. They have also been widely used in scientific publishing for graphs and diagrams to be embedded in articles or books.

EPS Version 3.0 is the latest published version of the specification. See History Note below for more detail on the early chronology. Despite acknowledged shortcomings compared with more recent formats, its widespread adoption by certain industry segments and in important workflows, means that it is still in common use. Several aspects of the format reflect the technology environment of the late 1980s. In particular, the specification defines variations specific to the primary personal computer operating systems in use at the time, Macintosh and DOS.

A typical EPS file contains not only the PostScript code that defines the image in a form that can be transmitted to a PostScript printer without information loss, but also a "preview" image in a format intended for convenient use in a workflow that involves several systems or applications. The intent of a preview is to have an image in a format that most graphics applications can render; a preview is usually of lower resolution, in pixel dimensions and/or in bit-depth. The preview file can be in one of a number of formats. The specification for EPS_3 lists three "device-specific" preview formats: for the Apple Macintosh, a PICT image as used by the QuickDraw application; for DOS computers, a TIFF bitmap or Windows Metafile. PICT and Windows Metafile can incorporate both bitmap data and vector graphics. In addition, the specification defines a very simple device-independent representation for an embedded bitmapped preview image. This representation is known as Encapsulated PostScript Interchange Format, or EPSI. An EPSI preview is a bitmap represented as ASCII hexadecimal, wrapped between a few PostScript comments for identification and intended to be simple and easily transportable. In order to distinguish EPS files with the different preview formats, different DOS file extensions and Macintosh file types were recommended in the EPS specification. See Notes below for more detail. The Wikipedia entry for Encapsulated PostScript states that the DOS/Windows format with a TIFF preview is the most widely supported variant. In the Macintosh version of some Adobe graphics applications, the options for saving or exporting EPS files include the use of PICT previews. The compilers of this resource have not been able to determine whether the other preview variants are still in use. Comments welcome. An attempt to open an EPS file in many graphics applications will present the preview without any indication that the rendered image is not the main image.

EPS files use lines of 255 or fewer ASCII characters. The specification recommends 7-bit ASCII. Lines may be terminated by any of the new line character combinations: CR (hex 0D), LF (hex 0A), CR LF, or LF CR.

The PostScript code that specifies an EPS image is subject to constraints, specified in the PostScript Language Document Structuring Conventions Specification (DSC). DSC is a set of conventions for PostScript documents, based on the use of comments. The structure of the file and its characteristics are exposed through comments introduced with '%' characters. The comments provide a standard way expose the structure to systems other than PostScript interpreters in a machine-readable way. Most importantly, an EPS file must include two required DSC header comments:

• %!PS-Adobe-3.0 EPSF-3.0This provides a magic number for identifying an EPS 3.0 file. For version 3.1 the string is "%!PS-Adobe-3.1 EPSF-3.0".
• '%%BoundingBox: llx lly urx ury'The four arguments of the bounding box comment correspond to the lower-left (llx, lly) and upper-right (urx, ury) corners of the bounding box.

In addition to these mandatory comment lines, a compliant EPS file uses additional comments to indicate structure and features. For example, specific comments are used to indicate that certain PostScript language versions or extensions must be present in the interpreter used for printing.

The EPS specification is brief and its effective use requires an understanding of the structure and context of the underlying PostScript Language and of the technological environment of the late 1980s. The EPS file format from Prepressure.com provides a more informal introduction and more current contextual information about the format together with practical guidance.

Adobe has stated that there will be no further versions of the PostScript Language or the EPS Specification, but Adobe's existing PostScript technology will continue to be available to license to commercial partners whose customers require it. See History Notes below for a specific statement that discusses EPS. As enhancements to the imaging model have been needed, Adobe has made them in PDF and not in the PostScript language.

In 2017, security threats were identified and exploited in EPS files. As a result, Microsoft disabled its import filter for EPS in distributions of its Office products; customers requiring EPS support must make registry changes in their Windows operating system. See Notes and Useful References below for more details on security issues related to the EPS format and networked PostScript printers.