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Subject: PostScript monthly FAQ v2.3 07-07-94 [11 of 11] Newsgroups: comp.lang.postscript,comp.answers,news.answers From: Jonathan Monsarrat <postscript-request@cs.brown.edu> Date: Mon, 7 Nov 1994 20:06:03 GMT Archive-name: postscript/faq/part11 Last-modified: 1993/07/07 Version: 2.3 -- PostScript -- Answers to Questions (the comp.lang.postscript FAQ v2.3) Jon Monsarrat jgm@cs.brown.edu This FAQ is formatted as a digest. Most news readers can skip from one question to the next by pressing control-G. GNUs uses C-c C-n to skip to the next question. Changes since the last version are marked with a '|' in the table of contents and in the sections in the text-only format of the FAQ. Now that there is Linux and NetBSD and BSD 386 UNIX IBM PC (and clone) users can run any of the X-windows and UNIX programs in the utilities section. See any of comp.os.linux.{ admin,development,help,misc}. Also, there is now GhostScript for the Macintosh. Many thanks to Dan Carrigan for reformatting the books and publishers section. The utilities index from the comp.sources.postscript FAQ will be posted in comp.lang.postscript now too. Please help fix the FAQ! All comments should be mailed to jgm@cs.brown.edu. My favorite way to receive a change suggestion is when it is accompanied by a section of the FAQ that is edited and mailed to me verbatim as an example. If you would like to contribute, please read the section ``about the FAQ'' first. Thank you! Books and programs are referred to by name only. See the book sections for book information, and the comp.sources.postscript FAQ for a full list of all PostScript related programs. I have archived a number of the small utilities in wilma.cs.brown.edu:pub/postscript. You can get the comp.sources.postscript FAQ from wilma.cs.brown.edu:pub/comp.sources.postscript. Related FAQs: comp.text, comp.text.tex, comp.fonts, comp.graphics, comp.sys.mac.apps, comp.sources.postscript. ------------------------------ Subject: 11 About PostScript 2 ------------------------------ Subject: 11.1 What printers support Level 2 PostScript? * Apple LaserWriter IIf * Apple LaserWriter IIg * Apple LaserWriter Pro 600 (with ram upgrade to get 600 DPI) * Apple LaserWriter Pro 630 (True 600 DPI) * Apple Personal LaserWriter NTR Apple sells an upgrade to the IINTX to turn it into a IIf/IIG for instance. * Compaq PAGEMARQ 20 * Compaq PAGEMARQ 15 * Data Products LZR 960 * Data Products LZR 1560 * DEClaser 1152 * Hewlett-Packard PostScript CartridgePlus, which works with the HP Laserjet III, IIID, and IIIP. * Hewlett-Packard LaserJet 4M * NEC SilentWriter 95 * QMS 1725 Print System * QMS 860 ``Hammerhead'' * QMS ColorScript 210 and 230 * Tektronix Phaser III PXi * Tektronix Phaser II (all models) * Tektronix Phase 200e * Texas Instruments microLaser Turbo * Texas Instruments microLaser XL Turbo This rest of file contains a description of PostScript 2 written by Carl Orthlieb from Adobe. The text has not been changed, but some paragraphs have been deleted for brevity. Comments by me are in square brackets, and these were not written by Adobe. ------------------------------ Subject: 11.2 What is PostScript Level 2? Since its introduction in 1985, the PostScript language has been considerably extended for greater programming power, efficiency, and flexibility. Typically, these language extensions have been designed to adapt the PostScript language to new imaging technologies or system environments. While these extensions have introduced new functionality and flexibility to the language, the basic imaging model remains unchanged. PostScript Level 2 integrates the original PostScript language, all previous language extensions, and new language features into the core PostScript language imaging model. ------------------------------ Subject: 11.3 [ Color Extensions ] The color extensions were added to the language in 1988 to provide more complete color functionality. With the original PostScript language, color could be specified using the red-green-blue (RGB) and hue-saturation-brightness (HSB) color models. The color extensions include cyan-magenta-yellow-black (CMYK) color model, black generation and undercolor removal functions, screen and transfer functions for four separate color components, and a colorimage operator for rendering color sampled images. The color extensions are currently found in PostScript color printers from Canon, QMS, Oce, and NEC as well as all implementations of the Display PostScript system. ------------------------------ Subject: 11.4 [ Composite Font Extensions ] The composite font technology is a general solution that extends the basic PostScript language font mechanism to enable the encoding of very large character sets and handle non-horizontal writing modes. A Type 1 PostScript font has room for encoding only 256 distinct characters. A typical Japanese font has over 7,000 Kanji, katakana and hiragana characters. The composite font technology allows you to create one ``composite'' font that is made up from any number of ``base'' fonts. In addition, the composite font technology allows you to include two sets of metrics (character spacing details) in the font: one for a horizontal-writing mode, and one for a vertical-writing mode. ------------------------------ Subject: 11.5 [ Display PostScript Extensions ] The Display PostScript extensions address the needs of using the PostScript language imaging model in a display environment. It includes extensions to deal specifically with displays and windowing systems as well as many optimized operators to increase performance which is critical in an interactive display environment [ (and printers) ] . ------------------------------ Subject: 11.6 [ Overview of Level 2 Features ] ------------------------------ Subject: 11.7 Filters * A filter transforms data as it is being read from or written to a file. The language supports filters for ASCII encoding of binary data, compression and decompression, and embedded subfiles. Properly used, these filters reduce the storage and transmission cost of page descriptions, especially ones containing sampled images. Benefits: Reduced storage requirements, greater performance. * ASCII encoding of binary data: ASCII/85 (represent binary data in ASCII format with only a 125 % expansion of data), and ASCII/HEX (current method of representing binary data in ASCII format but with a 200 % expansion of data). Benefits: Compact representation of binary data in a portable ASCII representation. * Compression and decompression filters: CCITT Group 3 & 4 (monochrome images), run-length encoding (monochrome and grayscale images), LZW ( 2:1 compression of text files), DCT (20-200:1 compression of color images using the proposed JPEG standard). Benefits: Improved performance due to reduced transmission times. PostScript files on disk can also be made much smaller, saving disk space. ------------------------------ Subject: 11.8 Binary Encoding In addition to the standard ASCII encoding, the language syntax includes two binary-encoded representations. These binary encodings improve efficiency of generation, representation, and interpretation. However, they are less portable than the ASCII encoding and are suitable for use only in controlled environments. Benefits: performance, compactness. ------------------------------ Subject: 11.9 Optimized graphics operators * Rectangle operators. New operators for filling, clipping and stroking rectangles; all highly optimized. For example, rectfill is 3 times faster than an equivalent moveto, lineto, lineto, lineto, closepath, fill. Benefits: performance and convenience. * Graphics state objects provide a fast way to switch between graphics states, which define the current line weight, color, font, etc. In existing printers, graphics states are stored on a stack, so accessing an arbitrary graphics state is somewhat cumbersome. With graphics state objects, the graphics state can be associated with a name, and retrieved by simply requesting the name. Benefits: Performance, convenience. * Halftone specification. New halftone dictionaries provide a more precise way of specifying the halftone dots, and makes switching between halftone screens faster. (The spot function is not reinterpreted.) Benefits: Performance, convenience, enhanced functionality. * User paths are self-contained procedures that consists entirely of path construction operators and their coordinate operands. User path operators perform path construction and painting as a single operation; this is both convenient and efficient. There is a user path cache to optimize interpretation of user paths that are invoked repeatedly. Benefits: Performance, convenience. * Stroke adjustment. For very thin lines, there is a trade-off between perfect positioning and consistent line width. Depending on the placement of such a line, it could end up being rendered as either 1 or 2 pixels wide, which is a noticeable difference. To account for this, PostScript language programs often include logic to slightly alter the coordinates of lines for consistent rendering. With automatic stroke adjustment the interpreter performs this adjustment to ensure consistent widths. Doing it in the interpreter rather than in the PostScript language program is 20 - 30 % faster. Benefits: Performance, convenience, improved quality. ------------------------------ Subject: 11.10 Optimized text operators * The xyshow operator provides a more natural way for applications to deal with individual character positioning. Allows simultaneous track kerning, pair kerning, and justification. Benefits: Performance, convenience. * The selectfont operator optimizes switching between fonts. It does the work of 3 Level 1 operators: findfont, scalefont, and setfont and has been optimized by using a caching mechanism. Benefits: Performance, convenience. ------------------------------ Subject: 11.11 Forms * A form is a self-contained description of any arbitrary graphics, text, and sampled images that are to be painted multiple times on each of several pages or several times at different locations on a single page. * With the new forms feature, you can define a base form whose representation stays cached between pages, so only information that changes between forms will need to be interpreted for each page. The representation used to cache the form may vary from device to device depending on the available resources, such as memory and/or hard disk space. In some cases, the actual rasterized form will be saved, in other cases, an intermediate representation (such as a display list) may be saved. Benefits: End-users will benefit by improved performance. * This makes forms processing faster and provide a natural framework for ISVs implementing a forms functionality in their application. Benefits: Convenience for ISVs. * Besides the traditional concept of ``forms,'' some other examples of forms include: Letterhead, stationary, overhead presentation backgrounds, repetitive symbols in a CAD drawing such as screws (mechanical drawing) or windows (architectural drawing), complex background blends in 35mm slides. Benefits: Enhanced functionality and application of PostScript printers in a variety of different environments. ------------------------------ Subject: 11.12 Patterns * The new pattern color space provides the ability to establish a pattern as the current color. Subsequent use of operators such as fill, stroke, and show apply ``paint'' that is produced by replicating (or tiling) a small graphical figure called a pattern cell at fixed intervals in x and y to cover the areas to be painted. The appearance of a pattern cell is defined by a PostScript language procedure, which can include any arbitrary graphics, text, and sampled images. The shape of the pattern cell need not be rectangular, and the spacing of tiles can differ from the size of the pattern cell. Benefits: Enhanced functionality, performance, convenience. * For efficiency, the representation of the pattern cell may be cached. When cached, the execution of the procedure that defines the pattern need be done only once for the current pattern. The pattern cache is similar to the font cache. Benefits: Performance. * Multiple colors can be specified in the pattern or the pattern can be used as a mask to paint a color defined in some other color space. Benefits: Enhanced functionality * For display environments, this feature will allow patterns to be represented in a resolution independent manner. Until now, patterns have typically been represented by arrangements of pixels. This resolution-dependent representation does not work well when trying to image the pattern at a variety of different resolutions. ------------------------------ Subject: 11.13 Images There are several enhancements to the facilities for painting sampled images: use of any color space, 12-bit component values, direct use of files as data sources, and additional decoding and rendering options. Benefits: Convenience, performance, quality. ------------------------------ Subject: 11.14 Composite Fonts * Provides the basic machinery for non-Roman character sets. Enables the encoding of very large character sets and non-horizontal writing modes. Benefits: Enhanced functionality. * Provides a page description language for international business. Composite font technology makes printers more international. The same font technology can be used worldwide, and will provide support for companies that must work in today's international business environment. Benefits: Enhanced functionality. * Advantages not limited to foreign languages - also useful for strictly Roman printers: allows the creation of a single composite font that combines two or more fonts. For example, you may wish to combine a textual font (such as Times-Roman) with a graphical font (such as Zapf-Dingbats), and have all characters at their disposal within a single font. Other uses of composite fonts: IBM extended character set, and expert sets (such as Adobe Garamond). Benefits: Enhanced functionality and increased performance by minimizing switching between fonts. ------------------------------ Subject: 11.15 New Color Spaces * CMYK color model and support for color images. Enhanced functionality. This will encourage more ISVs to use the color operators, because the operators will be widely available (The printer itself may not be able to print in color, but the PostScript language program won't generate errors when the operators for CMYK color are used.) * PostScript Level 2 supports several device-independent color spaces based on the CIE 1931 (XYZ)-space. CIE-based color specification enables a page description to specify color in a way that is related to human visual perception. The goal of the CIE standard is that a given CIE-based color specification should produce consistent results on different color output devices, independent of variations in marking technology, ink colorants, or screen phosphors. True device-independent color specification. Improved color matching between devices. * PostScript Level 2 supports three classes of color spaces: device independent, special, and device dependent. The following device independent color spaces are standard: The CIEBasedABC color space is defined in terms of a two-stage, non- linear transformation of the CIE 1931 (XYZ)-space. The formulation of the CIEBasedABC color space models a simple zone theory of color vision, consisting of a non-linear trichromatic first stage combined with a non-linear opponent color second stage. This formulation allows colors to be digitized with minimum loss of fidelity; this is important in sample images. Special cases of CIEBasedABC include a variety of interesting and useful color spaces, such as the CIE 1931 (XYZ)-space, a class of calibrated RGB spaces, a class of opponent color spaces such as the CIE 1976 (L*a*b*)-space and the NTSC, SECAM, and PAL television spaces. The CIEBased A color space is a one-dimensional and usually achromatic analog of CIEBasedABC. The following special color spaces are standard: * The Pattern color space enables painting with a ``color'' defined as a pattern, a graphical figure used repeatedly to cover the areas that are to be painted. See the discussion of patterns for more information. * The Indexed color space provides a way to map from small integers to arbitrary colors in a different color space such as a device independent color space. * The Separation color space provides control over either the production of a color separation or the application of a device colorant, depending on the nature and configuration of the device. The following device dependent color spaces are standard: * The DeviceGray color space is equivalent to the existing PostScript language's gray color model. * The DeviceRGB color space is equivalent to the existing PostScript language's red-green-blue (RGB) color model. * The DeviceCMYK color space is equivalent to the existing PostScript language's cyan-magenta-yellow-black (CMYK) color model. ------------------------------ Subject: 11.16 New screening/halftoning technology * Improved algorithms for determining the angles and frequencies used for halftone screens. The improvements fall into two primary categories: general improvements, and improvements specific to color separations. * General improvements: (1) The new algorithms yield a 10 % improvement in the speed of the setscreen and image operators; (2) Earlier version of PostScript software could produce halftone screens only for certain angle and frequency combinations. Enough of these combinations were available so that any requested screen could be fairly well approximated by one of the available angle and frequency combinations. In contrast, the improved halftoning algorithms can provide as much as a ten-fold increase in the number of angle-frequency combinations that are available, depending on the device resolution and the available memory. Benefits: Increased performance and higher quality halftone screens. * Improvements specific to color separations: An additional feature is available that enables PostScript software to generate extremely accurate screen angles and frequencies. The screens produced by this method can achieve an angular accuracy of within 05 degrees or better, depending on such parameters as exact screen angle requested, device resolution, and memory available for use by the algorithm. Benefits: Extremely high-quality color separations that approach the quality that previously was available only from high-end, color electronic pre-press systems. ------------------------------ Subject: 11.17 Improved printer support features * Page device setup provides a device independent framework for specifying the requirements of a page description and for controlling both standard features, such as the number of copies, and optional features, such as duplex printing, paper trays, paper sizes, and other peripheral features. * Applications developers will be able to write a single driver for a variety of different PostScript printers. The same code can be used to address printer specific features whether the features exist in the printer or not. If the feature is not in the printer, the application can decide how to best respond to the lack of the feature. Benefits: Enhanced functionality. ISVs benefit by having a more uniform method for accessing printer specific features. End users benefit by having software that will take advantage of their printer's features. ------------------------------ Subject: 11.18 Interpreter parameters Administrative operations, such as system configuration and changing input-output device parameters, are now organized in a more systematic way. Allocation of memory and other resources for specific purposes is under software control. For example, there are parameters controlling the maximum amount of memory to be used for VM, font cache, pattern cache, and halftone screens. Benefits: Flexibility. ------------------------------ Subject: 11.19 Resources * A resource is a collection of named objects that either reside in VM or can be located and brought into VM on demand. There are separate categories of resources with independent name spaces - for example, fonts and forms are distinct resource categories. * The language includes convenient facilities for locating and managing resources. ------------------------------ Subject: 11.20 Dictionaries Many Level 2 operators expect a dictionary operand that contains key-value pairs specifying parameters to the operator. Language features controlled in this way include halftones, images, forms, patterns, and device setup. This organization allows for optional parameters and future extensibility. For convenience in using such operators, the PostScript language syntax includes new tokens, << and >>, to construct a dictionary containing the bracketed key-value pairs. Benefits: Convenience, extensibility. ------------------------------ Subject: 11.21 When did Level 2 products come available? The first Level 2 products were available in early 1991. Level 2 printers will soon be much more common. ------------------------------ Subject: 11.22 Are Level 1 and Level 2 implementations compatible? [ Mostly, but not fully. The incompatibilities are of sufficient magnitude that when QMS introduced its first Level 2 compatible printer, it provided a ``Level 1'' mode for backward compatibility, for handling jobs which wouldn't run in Level 2. This should not be taken as too much of a criticism...some of the incom- patibilities from Level 1 to Level 2 involved fixing design mistakes in Level 1, or tightening up definitions which had been loose in Level 1 (where careless application writers had made use of the looseness, writing not to the language specification but to particular implementations.) ] (C) 1990 Adobe Systems Incorporated. All rights reserved. PostScript, Display PostScript, and Adobe are trademarks of Adobe Systems Incorporated registered in the U.S. All other product names are trademarks or registered trademarks of their respective