PostScript is a powerful and universal tool for desktop publishing (DTP).
It can be used on any kind of computer, whatever its operating system.
PostScript Basics
qqqqqqqqqqqqq
The PostScript Language
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
PostScript is a Page Description Language (PDL) that describes the presentation of an image in a form that’s understood by any PostScript device — usually a PostScript printer. Anything from aPostScript font to an entire document (such as a PostScript file) can be downloaded from a computer into a PostScript printer for printing. These descriptions always give the best possible results on a printer, irrespective of it’s resolution.
A PostScript printer accepts descriptions on one of three levels. If it receives descriptions at a lower level it takes these as well — but it can’t accept instructions at a higher level! Hence a PostScript Level 2 printer can accept Level 1 and Level 2 descriptions but a PostScript Level 1 printer can’t use those at Level 2.
Level 1 is highly reliable but can’t support any more than 256 characters per font, making it unsuitable for Chinese or other pictographic languages. Level 2, on the other hand, supports thousands of characters, gives better colour matching and is faster.
Level 3 (not yet available) creates 3D, full-range colour or half-tone images (with over 256 grey levels) and non-Roman characters. It can process HTML or PDF files, allows more fonts inside a printer and lets each PostScript device have a Web page on the Internet.
PostScript Data
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
PostScript can send the following kinds of data to a printer:-
z Font
A font of specified typeface or style that can be scaled to any size without
distortion and whose angle can be adjusted continuously to create various
oblique styles. The PostScript outline font descriptions can be obtained from
the printer itself or from the Mac’s Fonts folder.
z Text
This is reproduced using the last selected font.
z Object-Orientated Graphic
A description of a graphic element — a line can be described by its length,
thickness, start point and end point.
z Bitmap Graphic
Each pixel in a bitmap is reproduced on a typical 300 dpi laser printer by means
of a square of 4 x 4 laser dots at 75 lines per inch. The printed image may be
reduced by 4% to align the dots with the pixels shown on a Mac’s 72 dpi screen.
z Grey Scale Data
Data used with a bitmap (see above) to create a half-tone image.
√π See the Fonts chapter for details about PostScript fonts
PostScript in Operation
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
Most applications use the Mac’s own QuickDraw system to create images on the screen or on a non-PostScript printer. When such an image is required on a PostScript printer it’s converted into PostScript form by means of an appropriate printer driver file in the Extensions folder (in the System Folder).
Some applications avoid this conversion by working purely in a PostScript environment (using QuickDraw only for the screen image). Such applications may not work or may give poor results with a non-PostScript printer.
Any PostScript printer can convert PostScript code into a bitmap by rasterising the image. It does this by means of its powerful built-in Raster Image Processor (RIP). Most PostScript printers are laser devices with a resolution of 300, 600 or 1200 dpi. All Apple PostScript machines use AppleTalk, which makes them ideal for a network.
Some printers can also emulate a Diablo 630 daisy-wheel printer (using 12-point Courier font) or take instructions in Hewlett-Packard’s Printer Control Language 4 (PCL4) or PCL5.
› Some non-PostScript printers use a software form of RIP. This lets you use the
printer as if it were a real PostScript device.
LaserWriter Extra Features
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
  Some LaserWriters incorporate PhotoGrade software to adjust the size
and position of the printer’s laser, resulting in a significant
improvement in half-tone image quality. A 300 dpi machine with
PhotoGrade will give 50% more visible shades than a standard 600 dpi
machine. You must print a set of calibration sample pages via the
utility and then pick the best page. You enter your choice into the Mac
and the printer then uses this calibration for all future printing.
FineGrade is a much simpler algorithm, available in some printers to
smooth out the more jagged parts of text and graphics.
PostScript Software
qqqqqqqqqqqqqq
Applications
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
A wide range of PostScript-based applications are available, many of them produced by Adobe. For desktop publishing (DTP) PageMaker provides a convenient pasteboard environment — you can slide material from the board into your publication. Each story can be compiled as a block of text which can then be flowed into a ready-designed layout. It’s a powerful application but requires a fast computer for best effect.
For graphics work you could use Illustrator and/or Freehand — plus Photoshop for manipulation of high-quality images. All of these applications are rather expensive
— but then they are professional products!
› Some PostScript-based applications only work properly with a PostScript printer.
› Images used in PostScript applications such as PageMaker are always opaque. This
means they always hide anything that’s in the background.
› Adobe Type Manager lets you print PostScript fonts on a non-PostScript printer
— but it doesn’t support PostScript graphics or other features.
LaserWriter Utility
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
  This application, supplied with the system, can download fonts or PostScript files
into a PostScript printer. It can set various options for any selected PostScript
printer — but not all printers use all of the features in the utility.
√π See Fonts for details on the LaserWriter Utility and fonts
Here’s a summary of what LaserWriter Utility can do:-
General Controls
Change the printer name
Enable or disable the test page when the printer is first powered
Assign the printer to a different EtherTalk zone
Set an idle time before the printer powers down — this saves power
Restart the printer — this clears out all downloaded fonts
Download a PostScript file
Count the number of pages printed
Set the size of paper in an automatic tray or enable tray switching
Print Quality
Set the print density for graphics - this sets the darkness
Select FinePrint or PhotoGrade quality
Switch the printer resolution between 300 and 600 dpi
Enable or disable higher quality text printing
Enable or disable higher quality greyscale printing
PostScript Files
qqqqqqqqqqqq
PostScript descriptions can be stored in a variety of file types:-
PostScript File (TEXT)
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
This file contains a PostScript description as pure text. In some Print dialogs you can create a PostScript file by selecting Disk File instead of the printer. At a later time, the resultant file can be downloaded to a PostScript printer with LaserWriter Utility (see above). The file may (or may not) contain the font descriptions necessary to print the document.
A PostScript file often contains lots of formatting data — typically 80 K for 5 K of real text. If you’re desperate, you can extract useful information by reading it with a text editor!
z To create a file without a PostScript printer :
Select a laser printer in the Chooser — the LaserWriter Select 310 avoids AppleTalk.
In the Print dialog select Print to PostScript file and choose Print Later.
z To view or print a file:
Use an application such as Illustrator, Freehand or GhostScript (Aladdin) — these
can also convert the file into a PICT, TIFF or EPSF version.
Encapsulated PostScript File (EPSF)
wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
An EPSF contains a PostScript description packaged together with extra information about the document. This file type is used for any one of the following:-
z Drawing
Usually described with PostScript, but QuickDraw commands can be used instead.
Often used for monochrome line art or where 256 colours or less are used.
z Painting
A bitmap using monochrome, greyscale, RGB or CMYK encoding.
z Page
A PostScript description of a page of text and graphics — or part of a page.
Placing & Importing EPSFs
Each EPSF has a header that indicates the dimensions of the file’s contents and how it’s to be placed in a final document. A file can be placed (and scaled or rotated) into another page without the receiving application knowing anything about the file’s contents.
Many applications that can place an EPSF can’t edit the appearance of the source EPSF itself. Worse still, if you’ve not got a PostScript printer you’ll only see its preview image (see below) — and they don’t look too good!
With an application that’s able to import an EPSF you can edit the original file. Sadly, many applications that appear to import EPSFs can only place them — or can only import Adobe Illustrator files. Unfortunately Illustrator files, of Creator ART3 and Type EPSF, are an incredibly simplified version of the real thing!
You may find a utility such as epsConverter useful for converting real EPSFs into the Illustrator variety. Once converted you can use these files with any application that accepts them — and edit their contents as well.
EPSF Preview Images
A source EPSF may contain a low resolution preview image to let you see what you’re placing into a destination document. This gives you some idea of the final result without having to load the entire file into RAM. If a preview image is missing when you place an EPSF into PageMaker you’ll only see a grey box.
Three methods are commonly used:-
Machine File Preview
Mac EPSF PICT resource of ID 256
MS-DOS . EPS TIFF or Windows Metafile before or after EPS code
MS-DOS .TXT EPSI Hex dump as a PostScript comment
The EPSI format uses what’s called an in-line preview.
Other Points to Note …
· Not all applications can open all varieties of EPSF.
· Before printing an EPSF you must check that all necessary fonts are already in the
printer. If not, you’ll need to include them in the EPSF or download them into it.
Don’t send fonts inside an EPSF to anyone else — you’ll break the copyright laws!
· A Showpage PostScript command may be added to the end of a file. This lets you print
the image before embedding it into another document — once embedded this
command is disregarded. Some applications automatically include this command.
· Some EPSFs are compressed using JPEG compression.
