666 lines
30 KiB
INI
666 lines
30 KiB
INI
PostScript(R) LEVEL 2 -- QUESTIONS & ANSWERS
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============================================
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PostScript Level 2, the first major new release of PostScript
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software since its introduction, is a unification and enhancement
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of the PostScript language based on the needs voiced by users of
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PostScript printers and Display PostScript(R) workstations,
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Independent Software Vendors (ISVs), and Original Equipment
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Manufacturers (OEMs). PostScript Level 2 contains a number of
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performance enhancements, is easier for software developers to use,
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and contains important new functionality such as device-independent
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color, forms handling and patterns support.
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*** What is PostScript Level 2?
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First, let's look at the current state of the PostScript language.
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The baseline of the language is defined by the PostScript Language
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Reference Manual, also known as the "red book." The red book defines
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the basic PostScript language imaging model functionality for line
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art, sampled images, text, and the RGB color model. Since its
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introduction in 1985, the PostScript language has been considerably
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extended for greater programming power, efficiency, and
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flexibility.
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Typically, these language extensions have been designed to adapt the
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PostScript language to new imaging technologies or system
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environments. While these extensions have introduced new
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functionality and flexibility to the language, the basic imaging
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model remains unchanged. The principal language extensions are:
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+ Color: The color extensions provide a cyan-magenta-yellow-black
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(CMYK) color model for specifying colors and a colorimage operator
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for painting sampled images. They also include additional rendering
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controls for color output devices.
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+ Composite fonts: The composite font extensions enhance the basic
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font facility to support character sets that are very large or have
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complex requirements for encoding or character positioning.
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+ Display PostScript: The Display PostScript system enables
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workstation applications to use the PostScript language and imaging
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model for managing the appearance of the display. Some of the
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extensions are specialized to interactive display applications,
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such as concurrent execution and support for windowing systems.
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Other extensions are more general and are intended to improve
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performance or programming convenience.
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When Adobe decided to add additional functionality to the PostScript
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language, we did not want to add the functionality in a piecemeal
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fashion and have it exist in some devices but not others. This makes
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life difficult for independent software vendors (ISVs) who write
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PostScript language programs. PostScript Level 2 integrates the
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original PostScript language, all previous language extensions, and
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new language features into the core PostScript language imaging
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model. PostScript Level 2 ensures application developers consistent
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functionality across all Level 2 devices. When an application images
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to a Level 2 device, it can be assured that a wide range of features
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will exist on that device and that these features can be exploited
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to their fullest for increased performance and functionality.
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*** What are the features of PostScript Level 2?
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PostScript Level 2 consolidates all of the current language
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extensions into one unified language and adds many new features. It
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is also upward compatible with the current generation of PostScript
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devices. Here is a brief list of what comprises PostScript Level 2:
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+ Existing PostScript language
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+ Color extensions
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+ Composite font extensions
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+ Display PostScript extensions
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+ Improved memory management
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+ CIE-based device-independent color
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+ Improved printer hardware features support
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+ Data and image compression and decompression
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+ Optimized graphics and text operators from the
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Display PostScript system
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+ New halftoning algorithms
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+ Forms support
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+ Patterns support
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+ Binary language encodings
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+ ATM font rendering technology
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*** What are the color extensions to the PostScript language?
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The color extensions were added to the language in 1988 to provide
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more complete color functionality. With the original PostScript
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language, color could be specified using the red-green-blue (RGB)
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and hue-saturation-brightness (HSB) color models.
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The color extensions include cyan-magenta-yellow-black (CMYK) color
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model, black generation and undercolor removal functions, screen and
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transfer functions for four separate color components, and a
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colorimage operator for rendering color sampled images.
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The color extensions are currently found in PostScript color
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printers from Canon, QMS, Oce, and NEC as well as all
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implementations of the Display PostScript system.
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*** Why would you want the CMYK color extensions in a black and white
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printer?
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In a nut-shell, compatibility between black-and-white and color
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Level 2 devices.
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Today, ISVs must handle PostScript color printers differently. For
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example, current monochrome laser printers does not contain the CMYK
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color extensions, and as a result PostScript language programs must
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emulate this functionality, which results in slower performance. All
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Level 2 implementations will include the CMYK color extensions as
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standard.
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*** What are the composite font extensions to the PostScript
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language?
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The composite font technology is a general solution that extends the
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basic PostScript language font mechanism to enable the encoding of
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very large character sets and handle non-horizontal writing modes.
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A Type 1 PostScript font has room for encoding only 256 distinct
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characters. A typical Japanese font has over 7,000 Kanji, katakana
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and hiragana characters. The composite font technology allows you
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to create one "composite" font that is made up from any number of
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"base" fonts. In addition, the composite font technology allows you
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to include two sets of metrics (character spacing details) in the
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font: one for a horizontal-writing mode, and one for a vertical-
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writing mode.
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*** Why would you want the composite font extensions in a roman
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printer?
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This technology is currently implemented only in Japanese language
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PostScript devices, but the composite font technology is a general
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solution that applies to any language. It allows for the creation
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of one composite font that combines two or more fonts. For example,
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you may wish to combine a text font (such as Times-Roman) with a
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special font (such as Zapf-Dingbats) and have all characters at your
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disposal within a single font.
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*** What are the Display PostScript Extensions to the PostScript
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language?
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The Display PostScript extensions address the needs of using the
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PostScript language imaging model in a display environment. It
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includes extensions to deal specifically with displays and windowing
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systems as well as many optimized operators to increase performance
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which is critical in an interactive display environment.
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*** Why would you want the Display PostScript extensions in a
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printer?
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Most of the functionality in PostScript Level 2 that comes from the
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Display PostScript extensions result in improved performance. This
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includes clipping, rectangle operators, and binary language
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encoding to name a few. Each of the new Level 2 features that come
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from the Display PostScript extensions are detailed later in this
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document.
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Another obvious reason is for compatibility between Display
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PostScript applications and PostScript Level 2 printers.
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*** Can you tell me more about the rest of the PostScript Level 2
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features?
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Sure. Here a brief overview of the important features and benefits
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of PostScript Level 2:
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Filters
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-------
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+ A filter transforms data as it is being read from or written to a
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file. The language supports filters for ASCII encoding of binary
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data, compression and decompression, and embedded subfiles.
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Properly used, these filters reduce the storage and transmission
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cost of page descriptions, especially ones containing sampled
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images. => Reduced storage requirements, greater performance.
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+ ASCII encoding of binary data: ASCII/85 (represent binary data
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in ASCII format with only a 125% expansion of data), and ASCII/HEX
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(current method of representing binary data in ASCII format but with
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a 200% expansion of data). => Compact representation of binary data
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in a portable ASCII representation.
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+ Compression and decompression filters: CCITT Group 3 & 4
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(monochrome images), run-length encoding (monochrome and grayscale
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images), LZW (~2:1 compression of text files), DCT (20-200:1
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compression of color images using the proposed JPEG standard).
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=> Improved performance due to reduced transmission times. PostScript
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files on disk can also be made much smaller, saving disk space.
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Binary Encoding
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---------------
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+ In addition to the standard ASCII encoding, the language syntax
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includes two binary-encoded representations. These binary encodings
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improve efficiency of generation, representation, and
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interpretation. However, they are less portable than the ASCII
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encoding and are suitable for use only in controlled environments.
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=> Performance, compactness.
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Improved underlying implementation
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----------------------------------
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+ Improved font disk cache. We have improved the backup of the font
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cache on printers with a hard disk. Font access methods for reading
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the font back into RAM are more efficient. Also, the management of
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the disk is improved, so it does not become fragmented. => Performance,
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enhanced functionality.
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+ ATM font rendering technology. => Improved performance (4-5 times
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faster in raw character building speed) and improved quality (most
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evident at small point sizes and low resolutions).
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Improved memory management system
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---------------------------------
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+ One pool of memory available for all resource needs (page image,
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font cache, path storage, downloadable fonts, etc.). Memory
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allocated dynamically to meet needs. In general, memory is more
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efficiently shared among different uses and arbitrary memory
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restrictions have been eliminated. => Eliminates arbitrary memory
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restrictions for imaging of more complex graphics.
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+ Opportunistic memory management scheme. In the current system, the
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PostScript language program must manage memory on a per page basis.
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New memory management operators allow more flexibility for programs
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to explicitly release unused memory resources by removing individual
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entries from dictionaries and removing font definitions in an order
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unrelated to the order in which they were created. => More efficient
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use of available memory.
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+ Automatic memory reclamation. VM is reclaimed automatically for
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composite objects that are no longer accessible, such as strings
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used by the show operator. A "garbage collector" will automatically
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reclaim other unused memory. => More efficient use of available memory.
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Optimized graphics operators
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----------------------------
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+ Rectangle operators. New operators for filling, clipping and
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stroking rectangles; all highly optimized. For example, rectfill is
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3 times faster than an equivalent moveto, lineto, lineto, lineto,
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closepath, fill. => Performance, convenience.
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+ Graphics state objects provide a fast way to switch between
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graphics states, which define the current line weight, color, font,
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etc. In existing printers, graphics states are stored on a stack,
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so accessing an arbitrary graphics state is somewhat cumbersome.
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With graphics state objects, the graphics state can be associated
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with a name, and retrieved by simply requesting the name.
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=> Performance, convenience.
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+ Halftone specification. New halftone dictionaries provide a more
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precise way of specifying the halftone dots, and makes switching
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between halftone screens faster. (The spot function is not
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reinterpreted.) => Performance, convenience, enhanced functionality.
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+ User paths are self-contained procedures that consists entirely
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of path construction operators and their coordinate operands. User
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path operators perform path construction and painting as a single
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operation; this is both convenient and efficient. There is a user
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path cache to optimize interpretation of user paths that are invoked
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repeatedly. => Performance, convenience.
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+ Stroke adjustment. For very thin lines, there is a trade-off
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between perfect positioning and consistent line width. Depending
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on the placement of such a line, it could end up being rendered as
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either 1 or 2 pixels wide, which is a noticeable difference. To
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account for this, PostScript language programs often include logic
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to slightly alter the coordinates of lines for consistent rendering.
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With automatic stroke adjustment the interpreter performs this
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adjustment to ensure consistent widths. Doing it in the interpreter
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rather than in the PostScript language program is 20 - 30% faster.
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=> Performance, convenience, improved quality.
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Optimized text operators
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------------------------
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+ The xyshow operator provides a more natural way for applications
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to deal with individual character positioning. Allows simultaneous
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track kerning, pair kerning, and justification. => Performance,
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convenience.
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+ The selectfont operator optimizes switching between fonts. It
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does the work of 3 Level 1 operators: findfont, scalefont, and
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setfont and has been optimized by using a caching mechanism.
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=> Performance, convenience.
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Forms
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-----
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+ A form is a self-contained description of any arbitrary graphics,
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text, and sampled images that are to be painted multiple timesQon
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each of several pages or several times at different locations on a
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single page.
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+ With the new forms feature, you can define a base form whose
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representation stays cached between pages, so only information that
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changes between forms will need to be interpreted for each page. The
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representation used to cache the form may vary from device to device
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depending on the available resources, such as memory and/or hard
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disk space. In some cases, the actual rasterized form will be saved,
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in other cases, an intermediate representation (such as a display
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list) may be saved. => End-users will benefit by improved performance.
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+ This makes forms processing faster and provide a natural
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framework for ISVs implementing a forms functionality in their
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application. => Convenience for ISVs.
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+ Besides the traditional concept of "forms," some other examples
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of forms include: Letterhead, stationary, overhead presentation
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backgrounds, repetitive symbols in a CAD drawing such as screws
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(mechanical drawing) or windows (architectural drawing), complex
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background blends in 35mm slides. => Enhanced functionality and
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application of PostScript printers in a variety of different environments.
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Patterns
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--------
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+ The new pattern color space provides the ability to establish a
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pattern as the current color. Subsequent use of operators such as
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fill, stroke, and show apply "paint" that is produced by replicating
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(or tiling) a small graphical figure called a pattern cell at fixed
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intervals in x and y to cover the areas to be painted. The
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appearance of a pattern cell is defined by a PostScript language
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procedure, which can include any arbitrary graphics, text, and
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sampled images. The shape of the pattern cell need not be
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rectangular, and the spacing of tiles can differ from the size of
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the pattern cell. => Enhanced functionality, performance, convenience.
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+ For efficiency, the representation of the pattern cell may be
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cached. When cached, the execution of the procedure that defines the
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pattern need be done only once for the current pattern. The pattern
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cache is similar to the font cache. => Performance.
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+ Multiple colors can be specified in the pattern or the pattern can
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be used as a mask to paint a color defined in some other color space.
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=> Enhanced functionality
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+ For display environments, this feature will allow patterns to be
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represented in a resolution independent manner. Until now, patterns
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have typically been represented by arrangements of pixels. This
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resolution-dependent representation does not work well when trying
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to image the pattern at a variety of different resolutions.
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Images
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------
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+ There are several enhancements to the facilities for painting
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sampled images: use of any color space, 12-bit component values,
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direct use of files as data sources, and additional decoding and
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rendering options. => Convenience, performance, quality.
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Composite Fonts
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---------------
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+ Provides the basic machinery for non-Roman character sets. Enables
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the encoding of very large character sets and non-horizontal writing
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modes. => Enhanced functionality.
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+ Provides a page description language for international business.
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Composite font technology makes printers more international. The
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same font technology can be used worldwide, and will provide support
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for companies that must work in today's international business
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environment. => Enhanced functionality.
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+ Advantages not limited to foreign languages - also useful for
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strictly Roman printers: allows the creation of a single composite
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font that combines two or more fonts. For example, you may wish to
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combine a textual font (such as Times-Roman) with a graphical font
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(such as Zapf-Dingbats), and have all characters at their disposal
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within a single font. Other uses of composite fonts: IBM extended
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character set, and expert sets (such as Adobe Garamond). => Enhanced
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functionality and increased performance by minimizing
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switching between fonts.
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New Color Spaces
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----------------
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+ CMYK color model and support for color images. Enhanced
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functionality. This will encourage more ISVs to use the color
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operators, because the operators will be widely available (The
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printer itself may not be able to print in color, but the PostScript
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language program won't generate errors when the operators for CMYK
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color are used.)
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+ PostScript Level 2 supports several device-independent color
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spaces based on the CIE 1931 (XYZ)-space. CIE-based color
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specification enables a page description to specify color in a way
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that is related to human visual perception. The goal of the CIE
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standard is that a given CIE-based color specification should
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produce consistent results on different color output devices,
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independent of variations in marking technology, ink colorants, or
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screen phosphors. True device-independent color specification.
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Improved color matching between devices.
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+ PostScript Level 2 supports three classes of color spaces: device
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independent, special, and device dependent.
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The following device independent color spaces are standard:
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The CIEBasedABC color space is defined in terms of a two-stage, non-
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linear transformation of the CIE 1931 (XYZ)-space. The formulation
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of the CIEBasedABC color space models a simple zone theory of color
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vision, consisting of a non-linear trichromatic first stage combined
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with a non-linear opponent color second stage. This formulation
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allows colors to be digitized with minimum loss of fidelity; this
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is important in sample images.
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Special cases of CIEBasedABC include a variety of interesting and
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useful color spaces, such as the CIE 1931 (XYZ)-space, a class of
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calibrated RGB spaces, a class of opponent color spaces such as the
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CIE 1976 (L*a*b*)-space and the NTSC, SECAM, and PAL television
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spaces.
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The CIEBased A color space is a one-dimensional and usually
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achromatic analog of CIEBasedABC.
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The following special color spaces are standard:
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The Pattern color space enables painting with a "color" defined as
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a pattern, a graphical figure used repeatedly to cover the areas
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that are to be painted. See the discussion of patterns for more
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information.
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The Indexed color space provides a way to map from small integers
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to arbitrary colors in a different color space such as a device
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independent color space.
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The Separation color space provides control over either the
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production of a color separation or the application of a device
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colorant, depending on the nature and configuration of the device.
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The following device dependent color spaces are standard:
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The DeviceGray color space is equivalent to the existing PostScript
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language's gray color model.
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The DeviceRGB color space is equivalent to the existing PostScript
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language's red-green-blue (RGB) color model.
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The DeviceCMYK color space is equivalent to the existing PostScript
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language's cyan-magenta-yellow-black (CMYK) color model.
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New screening/halftoning technology
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-----------------------------------
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+ Improved algorithms for determining the angles and frequencies
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used for halftone screens. The improvements fall into two primary
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categories: general improvements, and improvements specific to
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color separations.
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+ General improvements: (1) The new algorithms yield a 10%
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improvement in the speed of the setscreen and image operators; (2)
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Earlier version of PostScript software could produce halftone
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screens only for certain angle and frequency combinations. Enough
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of these combinations were available so that any requested screen
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could be fairly well approximated by one of the available angle and
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frequencey combinations. In contrast, the improved halftoning
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algorithms can provide as much as a ten-fold increase in the number
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of angle-frequency combinations that are available, depending on the
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device resolution and the available memory. => Increased performance
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and higher quality halftone screens.
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+ Improvements specific to color separations: An additional
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feature is available that enables PostScript software to generate
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extremely accurate screen angles and frequencies. The screens
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produced by this method can achieve an angular accuracy of within
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.05 degrees or better, depending on such parameters as exact screen
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angle requested, device resolution, and memory available for use by
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the algorithm. => Extremely high-quality color separations that
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approach the quality that previously was available only from high-end,
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color electronic pre-press systems.
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Improved printer support features
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---------------------------------
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+ Page device setup provides a device independent framework for
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specifying the requirements of a page description and for
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controlling both standard features, such as the number of copies,
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and optional features, such as duplex printing, paper trays, paper
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sizes, and other peripheral features.
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+ Applications developers will be able to write a single driver for
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a variety of different PostScript printers. The same code can be
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used to address printer specific features whether the features exist
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in the printer or not. If the feature is not in the printer, the
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application can decide how to best respond to the lack of the
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feature. => Enhanced functionality. ISVs benefit by having a more uniform
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method for accessing printer specific features. End users benefit
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by having software that will take advantage of their printer's
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features.
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Interpreter parameters
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----------------------
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+ 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. => Flexibility.
|
|
|
|
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.
|
|
|
|
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. => Convenience, extensibility.
|
|
|
|
|
|
*** 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.
|
|
|
|
|
|
*** 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.
|
|
|
|
|
|
*** When will Level 2 products be available?
|
|
|
|
The first Level 2 products should be available in early 1991. Exact
|
|
product delivery dates will be announced by our OEMs as usual.
|
|
|
|
|
|
*** 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.
|
|
|
|
|
|
*** 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.
|
|
|
|
|
|
*** 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.
|
|
|
|
|
|
*** 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
|
|
is ultimately the rated engine speed of the output device.
|
|
|
|
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.
|
|
|
|
|