Encapsulated PostScript (Printer Languages)

Encapsulated PostScript is File format of Adobe’s PostScript page description language used in high quality computer printers. EPS is device independent, images can be transferred between different applications as well as sized and printed on different (EPS-compatible or emulating) printers, without any loss of image quality. It exploits the full capabilities of the device it is used on. A typical usage of EPS is to save an illustration created in a drawing program as an EPS file and to import it into a page layout program such as InDesign or QuarkXPress. The layout artist would place and resize the image, which would either be the embedded preview or rendered directly from the PostScript code. The EPS images would be saved in the page layout program.
It can contain any combination of text, graphics, and images. An EPS file is the same as any other PostScript language page description, with some restrictions.

An EPS file must be a conforming file, that is, it must conform to the Adobe Document Structuring Conventions (DSC). 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 file should make no environment-sensitive decisions (the importing application may be trying to attain some special effect, and the EPS program shouldn’t mess this up), although it can use some device-dependent tricks to improve appearance such as a snap-to-pixel algorithm.

The EPS file 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 (eg. 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 file can contain any combination of text, graphics, and images. An EPS file is the same as any other PostScript language page description, with some restrictions.

EPS files also frequently include a preview picture of the content, for on-screen display. The idea is to allow a simple preview of the final output in any application that can draw a bitmap. Without this preview the applications would have to directly render the PostScript (PS) data inside the EPS, which was beyond the capabilities of most machines until recently. Another advantage of the image preview is that if the graphic contained by the EPS is not to be modified itself but e. g. only to be placed inside a page layout using a layout software, the computer has less work to display only the small size preview instead of the high resolution image.
There are three preview formats providing the preview option for different platforms:
• PICT (Apple Macintosh),
• TIFF (IBM compatible, especially Microsoft Windows),
• EPSI (platform independent).
PICT is a graphics file format introduced on the original Apple Macintosh computer as its standard metafile format. It allows the interchange of graphics (both bitmapped and vector), and some limited text support, between Mac applications, and was the native graphics format of QuickDraw. With the change to Mac OS X, PICT was dropped in favour of Portable Document Format (PDF) as the native metafile format, though PICT support is retained by many applications as it is so widely supported on the Mac.
A widely used bitmapped graphics file format developed by Aldus and Microsoft that handles monochrome, gray scale, 8-and 24-bit color. TIFF allows for customization, and several versions have been created, which does not guarantee compatibility between all programs.TIFF files are compressed using several compression methods. LZW provides ratios of about 1.5:1 to 2:1. Ratios of 10:1 to 20:1 are possible for documents with lots of white space using ITU Group III and IV compression methods (fax).
Portable Document Format (PDF)
Portable document format, a universal computer file format that preserves all the fonts, formatting, colors, and graphics of any source document, regardless of the application and platform used to create it; the open de facto standard for electronic document distribution worldwide.
A PDF file delivers the single “digital master” for use in electronic, printed, and mixed workflow environments, ensuring a consistency across all media types. The Adobe PDF file format is ideally suited for technical publications, as it can include photographic images, diagrams, graphs etc. The PDF document can be widely distributed across many computer platforms. To read the PDF format, you require a copy of the Adobe acrobat reader, which can be obtained free of charge from the Internet or from many magazine publications on distributed CD–ROM.
The PDF combines three technologies:
1. A sub-set of the PostScript page description programming language, for generating the layout and graphics.
2. A font-embedding/replacement system to allow fonts to travel with the documents.
3. A structured storage system to bundle these elements and any associated content into a single file, with data compression where appropriate.
PostScript Printer Descriptions (PPDs)
PostScript Printer Description (PPD) files are created by vendors to describe the entire set of features and capabilities available for their PostScript printers. It is a small file that contains information about the characteristics of a certain PostScript printer. These informations are used by the PostScript printer driver to provide full access to the printer’s features

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