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Archive-name: postscript-faq/part11
Last-modified: 1992/10/29
Version: 2.0

                              -- PostScript -- 

                            Answers to Questions 

                    (the comp.lang.postscript FAQ v2.0) 

                               Jon Monsarrat 

                              jgm@cs.brown.edu 


    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 
    appropriate sections for full information. I have archived a number 
    of the small utilities in wilma.cs.brown.edu:pub/postscript. 

    Table of Contents 

    11 About PostScript 2 
        11.1 What printers run PostScript 2? 
        11.2 Introduction 
        11.3 What is PostScript Level 2? 
        11.4 What are the features of PostScript Level 2? 
        11.5 What are the color extensions to the PostScript language? 
        11.6 Why would you want the CMYK color extensions in a black and 
        11.7 What are the composite font extensions to the PostScript 
        11.8 Why would you want the composite font extensions in a roman 
        11.9 What are the Display PostScript Extensions to the PostScript 
        11.10 Why would you want the Display PostScript extensions in a 
        11.11 Can you tell me more about the rest of the PostScript Level 2 
        11.12 Filters 
        11.13 Binary Encoding 
        11.14 Improved underlying implementation 
        11.15 Improved memory management system 
        11.16 Optimized graphics operators 
        11.17 Optimized text operators 
        11.18 Forms 
        11.19 Patterns 
        11.20 Images 
        11.21 Composite Fonts 
        11.22 New Color Spaces 
        11.23 New screening/halftoning technology 
        11.24 Improved printer support features 
        11.25 Interpreter parameters 
        11.26 Resources 
        11.27 Dictionaries 
        11.28 What's the feedback from Adobe's OEMs on PostScript Level 2? 
        11.29 How much ROM/RAM will it take for a Level 2 printer? 
        11.30 When did Level 2 products come available? 
        11.31 What about existing PostScript printers? Are they obsolete? 
        11.32 Are Level 1 and Level 2 implementations compatible? 
        11.33 When will the new red book be available? 
        11.34 How is Adobe positioning PostScript Level 2? 

    11 About PostScript 2 


    11.1 What printers run PostScript 2? 



    * Apple LaserWriter IIf 


    * Apple LaserWriter IIg 


    * 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 


    * Hewlett-Packhard PostScript CartridgePlus, which works with the 
      HP Laserjet III, IIID, and IIIP. 


    * NEC SilentWriter2, model 95 


    * Tektronix Phaser III PXi 


    * Tektronix Phaser II PXi 


    * Tektronix Phaser II PXe 


    * Tektronix Phaser IISD 


    * 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. 


    11.2 Introduction 

    PostScript Level 2, the first major new release of PostScript 
    software since its introduction, is a unification and enhancement 
    of the PostScript language based on the needs voiced by users of 
    PostScript printers and Display PostScript(R) workstations, 
    Independent Software Vendors (ISVs), and Original Equipment 
    Manufacturers (OEMs). PostScript Level 2 contains a number of 
    performance enhancements, is easier for software developers to use, 
    and contains important new functionality such as device-independent 
    color, forms handling and patterns support. 


    11.3 What is PostScript Level 2? 

    First, let's look at the current state of the PostScript language. 
    The baseline of the language is defined by the PostScript Language 
    Reference Manual, also known as the "red book." The red book 
    defines the basic PostScript language imaging model functionality 
    for line art, sampled images, text, and the RGB color model. 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. The principal language extensions are: 



    Color: 
      The color extensions provide a cyan-magenta-yellow-black (CMYK) 
      color model for specifying colors and a colorimage operator for 
      painting sampled images. They also include additional rendering 
      controls for color output devices. 


    Composite fonts: 
      The composite font extensions enhance the basic font facility to 
      support character sets that are very large or have complex 
      requirements for encoding or character positioning. 


    Display PostScript: 
      The Display PostScript system enables workstation applications to 
      use the PostScript language and imaging model for managing the 
      appearance of the display. Some of the extensions are specialized 
      to interactive display applications, such as concurrent execution 
      and support for windowing systems. Other extensions are more 
      general and are intended to improve performance or programming 
      convenience. 

    When Adobe decided to add additional functionality to the 
    PostScript language, we did not want to add the functionality in a 
    piecemeal fashion and have it exist in some devices but not others. 
    This makes life difficult for independent software vendors (ISVs) 
    who write PostScript language programs. PostScript Level 2 
    integrates the original PostScript language, all previous language 
    extensions, and new language features into the core PostScript 
    language imaging model. PostScript Level 2 ensures application 
    developers consistent functionality across all Level 2 devices. 
    When an application images to a Level 2 device, it can be assured 
    that a wide range of features will exist on that device and that 
    these features can be exploited to their fullest for increased 
    performance and functionality. 


    11.4 What are the features of PostScript Level 2? 

    PostScript Level 2 consolidates all of the current language 
    extensions into one unified language and adds many new features. It 
    is also upward compatible with the current generation of PostScript 
    devices. Here is a brief list of what comprises PostScript Level 2: 



    * Existing PostScript language 


    * Color extensions 


    * Composite font extensions 


    * Display PostScript extensions 


    * Improved memory management 


    * CIE-based device-independent color 


    * Improved printer hardware features support 


    * Data and image compression and decompression 


    * Optimized graphics and text operators from the 


    * Display PostScript system 


    * New halftoning algorithms 


    * Forms support 


    * Patterns support 


    * Binary language encodings 


    * ATM font rendering technology 


    11.5 What are the color extensions to the PostScript language? 

    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. 


    11.6 Why would you want the CMYK color extensions in a black and 
    white printer? 

    In a nut-shell, compatibility between black-and-white and color 
    Level 2 devices. 

    Today, ISVs must handle PostScript color printers differently. For 
    example, current monochrome laser printers does not contain the 
    CMYK color extensions, and as a result PostScript language programs 
    must emulate this functionality, which results in slower 
    performance. All Level 2 implementations will include the CMYK 
    color extensions as standard. 


    11.7 What are the composite font extensions to the PostScript 
    language? 

    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. 


    11.8 Why would you want the composite font extensions in a roman 
    printer? 

    This technology is currently implemented only in Japanese language 
    PostScript devices, but the composite font technology is a general 
    solution that applies to any language. It allows for the creation 
    of one composite font that combines two or more fonts. For example, 
    you may wish to combine a text font (such as Times-Roman) with a 
    special font (such as Zapf-Dingbats) and have all characters at 
    your disposal within a single font. 


    11.9 What are the Display PostScript Extensions to the PostScript 
    language? 

    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. 


    11.10 Why would you want the Display PostScript extensions in a 
    printer? 

    Most of the functionality in PostScript Level 2 that comes from the 
    Display PostScript extensions result in improved performance. This 
    includes clipping, rectangle operators, and binary language 
    encoding to name a few. Each of the new Level 2 features that come 
    from the Display PostScript extensions are detailed later in this 
    document. 

    Another obvious reason is for compatibility between Display 
    PostScript applications and PostScript Level 2 printers. 


    11.11 Can you tell me more about the rest of the PostScript Level 2 
    features? 

    Sure. Here a brief overview of the important features and benefits 

    of PostScript Level 2: 


    11.12 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. 


    11.13 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,z compactness. 


    11.14 Improved underlying implementation 



    * Improved font disk cache. We have improved the backup of the font 
      cache on printers with a hard disk. Font access methods for 
      reading the font back into RAM are more efficient. Also, the 
      management of the disk is improved, so it does not become 
      fragmented. Benefits: Performance, enhanced functionality. 


    * ATM font rendering technology. Benefits: Improved performance 
      (4-5 times faster in raw character building speed) and improved 
      quality (most evident at small point sizes and low resolutions). 


    11.15 Improved memory management system 



    * One pool of memory available for all resource needs (page image, 
      font cache, path storage, downloadable fonts, etc.). Memory 
      allocated dynamically to meet needs. In general, memory is more 
      efficiently shared among different uses and arbitrary memory 
      restrictions have been eliminated. Benefits: Eliminates arbitrary 
      memory restrictions for imaging of more complex graphics. 


    * Opportunistic memory management scheme. In the current system, 
      the PostScript language program must manage memory on a per page 
      basis. New memory management operators allow more flexibility for 
      programs to explicitly release unused memory resources by 
      removing individual entries from dictionaries and removing font 
      definitions in an order unrelated to the order in which they were 
      created. Benefits: More efficient use of available memory. 


    * Automatic memory reclamation. VM is reclaimed automatically for 
      composite objects that are no longer accessible, such as strings 
      used by the show operator. A ``garbage collector'' will 
      automatically reclaim other unused memory. Benefits: More 
      efficient use of available memory. 


    11.16 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. 


    11.17 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. 


    11.18 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. 


    11.19 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. 


    11.20 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. 


    11.21 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. 


    11.22 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. 


    11.23 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. 


    11.24 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. 


    11.25 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. 


    11.26 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. 


    11.27 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. 


    11.28 What's the feedback from Adobe's OEMs on PostScript Level 2? 

    The feedback has been overwhelmingly positive. We have always 
    believed that we are taking our OEMs, ISVs and end users best 
    interests into account in moving forward with the PostScript 
    language. The feedback we have received so far confirms that we are 
    doing the right thing on all fronts. 


    11.29 How much ROM/RAM will it take for a Level 2 printer? 

    As is true with our current implementations, RAM/ROM requirements 
    will vary from one device to the next depending on the specific 
    capabilities of each device. However, our estimates put the code 
    size at approximately 1.5 Mb of ROM (for CISC processors), and 1.5 
    Mb of RAM, minimum. 


    11.30 When did Level 2 products come available? 

    The first Level 2 products were available in early 1991. 


    11.31 What about existing PostScript printers? Are they obsolete? 

    The current generation of PostScript printers (which you could 
    think of as PostScript Level 1) will not become obsolete because of 
    Level 2 products. Think of Level 1 and Level 2 printers as a family 
    of products, each having its own set of features to suit the needs 
    of a particular customer. While we will continue to support and 
    build Level 1 products (based on our OEM's demands) we think that 
    over the next 12-18 months most of our OEMs will begin providing 
    PostScript Level 2 products. 


    11.32 Are Level 1 and Level 2 implementations compatible? 

    All existing programs that run on today's PostScript printers will 
    run on a Level 2 device. That is, PostScript Level 2 is upward 
    compatible with the existing installed base of printers and print 
    drivers. However, it is not 100 % backward compatible. A file 
    written specifically to take advantage of some Level 2 features 
    will not run on a Level 1 printer because some functionality cannot 
    be emulated. Most Level 2 features can be emulated on a Level 1 
    printer and an intelligent driver can conditionally use Level 2 
    features when available, and fall back on Level 1 operators when 
    not. The new red book will include an appendix that will help ISVs 
    deal specifically with compatibility issues. 


    11.33 When will the new red book be available? 

    A new version of the red book, called the PostScript Language 
    Reference Manual, Second Edition, will be published by Addison- 
    Wesley in December 1990. 


    11.34 How is Adobe positioning PostScript Level 2? 

    Adobe is positioning PostScript Level 2 as an integral part of a 
    total system solution for printing and display environments. 
    PostScript Level 2 software provides the foundation for Adobe's 
    OEMs to implement an entire spectrum of products from low-cost 
    desktop laser printers for office-automation to high-resolution 
    imagesetters for producing color separations. 

    Let's put PostScript Level 2 in perspective with respect to the 
    overall printing solution. The effectiveness and performance of any 
    particular printing solution is affected by four main elements: 



    * Driver: Each major system software environment (Macintosh, 
      Windows, OS/2 Presentation Manager, NeXT) has a built-in 
      PostScript language driver. These system level drivers ensure 
      that all applications running in the environment can output to 
      PostScript printers. These drivers do not always produce the most 
      efficient PostScript language programs, and may not support the 
      wide variety of features available in the language or specific 
      hardware features in a PostScript printer. 


    * Language: The PostScript language as defined in the PostScript 
      Language Reference Manual (the ``red book'') is the standard 
      today. 


    * Communications: AppleTalk, parallel, and serial communications 
      are the most commonly used interfaces with PostScript printers 
      today. 


    * Controller: Today, most Adobe PostScript printers are based on a 
      variety of controllers: Scout (68000), Atlas (68020), and Atlas 
      Plus (68030). In addition, there are a number of custom 
      controller solutions offered by our OEMs. Total system throughput 
      is a function of all four elements. An efficient driver can 
      produce PostScript page descriptions that print much faster; 
      speed increases of 2-3x over an inefficient driver are not 
      uncommon. Communications bottlenecks can account for a majority 
      of the time it takes to print a page; a very large scanned image 
      can take minutes to transmit to the printer, even using 
      AppleTalk. And of course, the speed of the controller itself has 
      a direct impact on the time it can take to print a page. However, 
      the limiting factor 

    PostScript Level 2 is one component of a total systems solution 
    being assembled by Adobe: 



    * Adobe is developing drivers for the Macintosh, Windows 3.0, and 
      OS/2 Presentation Manager environments. These drivers will take 
      full advantage of the features and performance enhancements in 
      PostScript Level 2 printers as well as existing PostScript 
      printers. 


    * PostScript Level 2 extends the PostScript language with new 
      operators to improve performance and provide additional 
      functionality to address the need of end users and ISVs. 


    * PostScript Level 2 includes a variety of file compression 
      techniques that can be used to reduce the amount of information 
      sent (and hence the time to do so) to the PostScript printer. 


    * Adobe is developing new controllers based on the latest RISC 
      technology which are up to 22 times faster than current 
      controllers. In addition, these controllers provide our OEMs the 
      potential for providing direct SCSI input and Ethernet 
      connections for increased throughput. 

    (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 
    holders.