Internet Surfer 2.0/Internet Surfer 2.0 (Wayzata Technology) (1996).iso/pc/text/mac/faqs.444

Text File | 1996-02-12 | 29KB | 709 lines

Frequently Asked Questions (FAQS);faqs.444




Subject: 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.


Subject: 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


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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:


Subject: 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.


Subject: 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.


Subject: 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).


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 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.


Subject: 11.30 When did Level 2 products come available?

    The first Level 2 products were available in early 1991.


Subject: 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.


Subject: 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.


Subject: 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, was be published by Addison-
    Wesley in December 1990, and was generally available around May of
    1991.


Subject: 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.