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What is an EPS Vector file format?



What is EPS vector file format?

EPS or Encapsulated PostScript is a standard graphics file format for exchanging images, drawings (such as a logo or map) or even layouts of complete pages. An EPS file internally contains a  description of such an object or layout using the PostScript page description language. It can include both bitmap and vector data.  The purpose of an EPS file is to be included in other pages. Sometimes EPS files are called EPSF files. EPSF simply stands for Encapsulated PostScript Format. EPS files have the extension .eps or .epsf.

This page discusses:

  • the basics of the EPS file format
  • how to create EPS files
  • how to view EPS thumbnails
  • how to reduce the file size of EPS files
  • More technical details about the file format

EPS is still in widespread use but it is essentially an outdated file format that no longer evolves.

  • For exchanging logos or drawings, it has been replaced by the native file formats of Adobe applications.Adobe have made it easy to drop a native Illustrator or Photoshop file in an InDesign document. Given that most people work with the Adobe Creative Cloud or Creative Suite software, EPS no longer makes sense as an intermediate file format.
  • For exchanging complete pages or advertisements, it has been replaced by PDF (just like PostScript itself is also being phased out and replaced by PDF).

What is EPS vector file format?Even though PDF and native file formats are the way to go, your existing library of EPS files will still remain usable for a long time. Here is what Dov Isaacs from Adobe said in a discussion on a PrintPlanet forum: “ …Adobe will continue to support EPS as a legacy graphics format for import of non-color managed, opaque graphical data into Adobe applications (such as InDesign and Illustrator). Although we certain do not recommend that new graphical content be stored in EPS format (except to satisfy the need to import data into page layout programs that aren’t quite PDF-centric — no need to mention names here!), our user base should feel comfortable that there is no need to worry about a need to convert their very sizable libraries of EPS-based graphic assets.”

The basics of EPS files

What is EPS vector file format?An EPS file can contain any combination of text, graphics and images. Since it is actually a PostScript file, it is one of the most versatile file formats that are available. EPS-files usually contain a small preview image that is used to visualize the content of the file. This is done so that applications don’t need a PostScript interpreter to display the content of the EPS file. Even office applications such as Microsoft Word can display the preview image. If an EPS file is sent to a printer that doesn’t support PostScript, it is once again this preview image that is printed. The quality will not equal that of the read EPS artwork but at least there is an image on the print-out. There are millions of people working with *.eps files without realising how complex the artwork they are using really is.

How to create EPS files

EPS files can be generated by all professional drawing applications as well as most layout applications.

  • The most widely used application to create EPS files is Adobe Illustrator. Illustrator’s native file format is called AI. An AI file is smaller than the corresponding EPS file and it retains all of the editing capabilities of Illustrator. The advantage of saving as an EPS is that it is easier to use the file with other (non-Adobe) applications. If you need to send artwork to another company and you do not know what software they will use to process your creation, use EPS or PDF.
  • Image manipulation programs like Adobe Photoshop can also save bitmap images as EPS-files.
  • Some printer drivers are capable of generating EPS-files as well as PostScript files.

 

How to view EPS files

Viewing placed EPS files

When you place an EPS file on a page in a layout or word processing application, that application needs to visualize the content of the EPS. It can do this in two different ways:

  • It can display the preview image that is embedded in the EPS file.
  • It can attempt to render the content of the EPS file and generate a preview image that is optimized for the current  screen size and magnification. Only a few applications, such as Adobe InDesign, are capable of doing this. Since this operation can be fairly processor intensive, InDesign will only do this if the display quality selected by the user is set to High.

Viewing EPS thumbnails in operating systems

Seeing the content of an EPS can be a real hassle, both on PCs and on Macintosh.

  • EPS thumbnails in Windows
    When an EPS-file is viewed in the thumbnail view of Windows Explorer, a generic icon is used. Below are for example 2 EPS-files viewed in Windows XP.

EPS-files in Windows XP

For other file formats such as JPG or PNG, Explorer shows a thumbnail of the actual image content. This can be very practical when dealing with large amounts of files. There is a little tool called PS+Ai Thumb which at least partly solves this problem. It works on some images but not on all types of EPS files, as shown below. I’ve only used it with Windows XP. It does not work on the 64-bit version of Windows 7.

EPS files in Explorer with installed

The best solution is to use a more dedicated image browser or viewer. Below is what Adobe Bridge displays. Bridge is bundled with applications such as the Adobe Creative Suite or Photoshop.

EPS files in Adobe Bridge

  • EPS previews in Mac OS X
    In Leopard the situation is a bit similar to that of Windows: viewing EPS thumbnails works fine in applications like Adobe Bridge but in the Finder or QuickLook you don’t see a preview. Fortunately there is an excellent plugin called EPSQLPlugIn which fixes this. It can be downloaded here.
    Apple eliminated this limitation in OS X 10.6. Below is how the above two icons look in the Finder in Snow Leopard.

Dinges

How to convert an EPS file to another file format

An EPS file can be converted to PDF, TIFF, JPG, PNG or other graphic file formats.

  • If you are an Adobe Illustrator or Photoshop user, just open the EPS file and use SAVE AS to export to another file format. CorelDraw and other drawing applications can also be used to do the same.
  • If you do not have any of the above mentioned applications, there are web sites that can convert an EPS to an image. Google and you shall find.

Keep in mind that converting an EPS that contains vector data to an image file format that only can contain bitmap data means you are converting to a file that is optimized to be used at one specific size. The page on bitmap versus vector graphics explains this in more detail.

How to reduce the file size of EPS files

Logos and other types of artwork are often saved as EPS files. It makes sense to try and keep the file size down. There are a number of things you can do to reduce the size of EPS data:

  • Often the preview image that is embedded in an EPS file makes up a large part of the EPS data. If you originally filled an landscape A4 or letter size canvas with a logo, the A4 or letter sized preview image can easily exceed half a megabyte. If the logo is a vector based drawing, there is no disadvantage in reducing its size and making it 10 centimeter or 4 inches wide. That may halve the file size of the EPS file.
  • An application like Adobe Illustrator saves additional information in its EPS output. When saving as an EPS file, you can select the file format. By selecting Illustrator 9 instead of Illustrator CS5, I shaved 200K off the file size of an EPS. Take into account that saving in an older file format may impact your ability to edit the EPS file afterwards.
  • Get rid of unnecessary data: In its Action window Adobe Illustrator has an option to delete unused palette items. This deletes unused color swatches, brushes, symbols and styles. That may reduce the file size by an extra 200 to 400 K. Also make sure that there isn’t any irrelevant artwork hidden in a deactivated layer or the pasteboard area.
  • Try optimizing the design by simplifying paths or merging multiple paths into a single one.
  • If the EPS file needs to contain bitmap images, make sure to use the optimum resolution for these.

Additional information can be found on this excellent page.

More in-depth information on the EPS file format

An EPS file must conform to the Adobe Document Structuring Conventions (DSC). These are a set of rules that define how PostScript data should be organized.

At a minimum, it must include a header comment, %!PS-Adobe-3.0 EPSF-3.0, and a bounding box comment, %%BoundingBox: llx lly urx ury, that describes the bounds of the illustration. (The specification does not require the EPSF version, but many programs will reject a file that does not have it.)

The EPS program must not use operators that initialize or permanently change the state of the machine in a manner that cannot be undone by the enclosing application’s use of save and restore (e.g.. the operators starting with “init” like initgraphics). As a special case, the EPS program may use the showpage operator. The importing application is responsible for disabling the normal effects of showpage. The EPS program should make no environment-sensitive decisions (the importing application may be trying to attain some special effect, and the EPS program shouldn’t screw this up), although it can use some device-dependent tricks to improve appearance such as a snap-to-pixel algorithm.

There are some operators that should not be used within an EPS file: banddevice, cleardictstack, copypage, erasepage, exitserver, framedevice, grestoreall, initclip, initgraphics, initmatrix, quit, renderbands, setglobal, setpagedevice, setshared and startjob. These also include operators from statusdict and userdict operators like legal, letter, a4, b5, etc. There are some operators that should be carefully used: nulldevice, setgstate, sethalftone, setmatrix, setscreen, settransfer and undefinefont.

EPS files can be encoded using 7-bits (ASCII, like PostScript data usually are) as well as 8-bits (binary, which is virtually always done on Macintosh because it decreases the size of the file significantly). 8 bit EPS-files cannot be handled properly by all operating systems or applications.

The image preview

EPS files can optionally contain a bitmapped image preview, so that systems that can’t render PostScript directly can at least display a crude representation of what the graphic will look like.

There are 4 preview formats:

  • PICT, mainly used in files generated on Macs. The PICT file is stored in the resource fork of the EPS file, while the actual PostScript data are stored in the data fork. PICT is the default file format of QuickDraw, the graphics model that is used by MacOS 7/8/9 applications to generate the screen display.
  • TIFF: Most EPS files created by Windows applications contain a TIFF file for preview purposes.
  • Metafile: Some EPS files originating on PC contain a Windows Metafile preview. WMF or Windows Metafile is the PC equivalent of the Macintosh PICT file format.
  • EPSI which is an EPS file with a platform device independent preview. EPSI is an all ASCII (no binary data or headers) version of EPS. EPSI provides for a hexadecimal encoded preview representation of the image that will be displayed or printed. EPSI files were documented by Adobe as a means of providing a preview for EPS files which would be cross-platform. In reality though DOS machines and Windows favour embedding TIFF or even Windows Metafiles in the PostScript. EPSI is mainly used on Unix systems.

It is also possible to have an EPS file without a preview though. In this case the imported file is usually displayed as a greyed out box or a box with diagonal lines running through it.

The preview image has a fixed resolution, which is usually 72 dpi. If you enlarge an EPS file in a document, the preview image is stretched and may become ‘blocky’ and lacking of detail. This does not necessarily mean that the EPS-data themselves will degrade in quality. As long as the EPS-file only contains text and vector graphics, scaling it does not affect its quality.

If you print a file containing an EPS-image on a non-PostScript printer, it is usually the preview image that gets printed. The preview image is ignored when you print to a PostScript device.

Remarks

Although an EPS file contains PostScript data, you cannot always sent it straight to a printer to have it printed. Some interpreters cannot handle the preview data that may be included in the EPS file. Others don’t output the file because the ‘showpage” operator is missing. It can also happen that the printer does process the job but outputs a blank page because the content of the EPS-file was located outside the printable area.

EPS-files can contain PostScript level 2 operators that make it impossible to output the file on an old PostScript level 1 device.

Specsheet

Name: EPS
Developer: Adobe
Release date: mid 80′s
Type of data: vector, bitmap & fonts
Number of colors: unlimited
Color spaces: ?
Compression algorithms: ?
Ideal use: information exchange between prepress applications
Extension on PC-platform: .EPS
Macintosh file type : EPSF (sometimes TEXT)