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C Glossary


Bilevel images contain only two colors: black and white. “Lineart” is another term for bilevel images.


Comité Consultatif International Téléphonique et Télégraphique, renamed to ITU-T in 1993. This group specified communication protocols for a particular class of devices (e.g. facsimile devices) and represents specific modes of compression (CCITT Group 3, CCITT Group 4).


Commission Internationale de l’Eclairage. The CIE is responsible for the definition of color models and the standardization of color descriptions. The Lab color space has been defined by the CIE.


Lab colors are defined by the L-value for lightness and the co-ordinates defining the quantitative distance of a color from a reference white point. The Lab color space includes all visible colors and is device independent.


Color printing is based on the CMYK color space. Cyan, Magenta, Yellow, and Black inks are mixed on paper to produce a given color. The definitions of the basic colors cyan, magenta, yellow, and black are slightly different in Europe (Euro), the US (SWOP), and Japan.

Color matching

The process of adjusting colors to achieve maximum similarity from the gamut of one color space to another. In practice, the color data delivered by a given device – e.g. a scanner – has to be transformed so that the colors can exactly be reproduced by a second device – e.g. a printer.

Color mode

See: Bilevel, Grayscale, Indexed colors, RGB, CMYK, CIELab, Spot color, Multichannel, Multitones.


ColorSync offers a programming interface to a fast computing engine which uses ICC profiles as parameters to perform color transformations between different devices. ColorSync has been co-developed by Apple Computer and Linotype-Hell.


See: LZW, CCITT, JPEG, JPEG 2000, JBIG2, PackBits RLE.

DeviceLink profile

The International Color Consortium (ICC) has defined ICC profiles which describe the color characteristics of graphics devices (such as scanners, monitors, and printers) and of abstract color spaces (such as CIELab D50, CIELab D65, and CIELuv). Additionally, the ICC has defined DeviceLink ICC profiles, which describe mappings from one particular color space to another particular color space, e.g. from an offset press CMYK color space to a gravure press CMYK color space. Many DeviceLink ICC profiles maintain special characteristics of the black channel and fulfill special conditions for color sums according to the drying capabilities of a particular printing process.


The process of transforming a high-resolution image into a low-resolution image.


See: Resolution


Encapsulated PostScript File (EPSF) is an image format. EPSF files contain a PostScript program. When their program is being interpreted, the image is re-created. EPSF files may additionally contain an image preview of the image. Many illustration and DTP applications can create EPSF files. Please note that Mac-EPSF files and PC-EPSF files (for Windows computers) are not identical. PC-EPSF files contain LZW- compressed TIFF previews (instead of PICT previews) and, therefore, behave different in specific situations.

Note that there are two fundamentally different types of EPSF files:
Vector (object) based EPSF, created by drawing programs such as Illustrator, and raster (bitmap) EPSF files, created by programs such as Photoshop, or scanners.


Extremely fast, reliable, feature-rich Apple compatible file and print server. Includes TCP printer drivers supporting mDNS (“Bonjour”) for easy printer selection on OS X clients.


Euro, formerly Euroscale, defines the European ink set for the process colors cyan, magenta, yellow, and black.

File format


Gamut, gamut mapping

The range of color that a given device can produce. Gamut mapping means re-defining the colors of a given device so that its gamut becomes (approximately) identical to that of a second device.


Grayscale images are a generalization of bilevel images. They contain black and white and different shades of gray.

Home directory

Private directory provided for each UNIX user. The home directory is the current directory as soon as you login to a server via Terminal.

ICC, ICC profiles

International Color Consortium. A group of vendors who defined the ICC profile format. This format is a cross-platform specification which allows third-party vendors to develop profile tools and applications supporting the ICC profile standard. The founding members of this consortium include: Adobe Systems Inc., Agfa-Gevaert N.V., Apple Computer Inc., Eastman Kodak Company, FOGRA (Honorary), Microsoft Corporation, Silicon Graphics Inc., Sun Microsystems Inc., and Taligent Inc. These companies have committed themselves to fully support this specification in their operating systems, platforms and applications.

Indexed colors

Images with indexed colors use colors from a given RGB color map. Every pixel of such an image contains a reference to a specific color in the map.


Joint Photographic Experts Group JPEG is a file format and – at the same time – a mode of compression. Images are compressed by replacing several similar colors by one color only. Thus, some color data gets lost and cannot be recreated when the files are opened again.

JPEG 2000

A potential successor to JPEG with better compression and multiresolution images. JPEG 2000 gives reasonable quality down to 0.1 bits/pixel. JPEG quality drops dramatically below about 0.4 bits/pixel. In addition, JPEG 2000 also allows lossless compression.


A compression standard for lossless bilevel image coding. JBIG2 has been developed by the Joint Bilevel Image Experts Group.


ImageServer generates low-resolution representations of high-resolution image files or PDF files. These representations are called “layout” files.


LZW (Lempel, Ziv, Welch – the names of developers) is a lossless compression that can be used for different color modes and file formats. It collects repetitive patterns in a table and saves references to this table whenever possible.


A multichannel image contains CMYK channels and one or more channels different from CMYK, which are all treated as process colors. The most famous example is Pantone Hexachrome.


Colorized Grayscale image.

PackBits RLE

Apple Mac OS compression, used e.g. in PICT files. See also: RLE.


PCShare is a high-end SMB-based file server and print server software for Windows computers which are attached to the host via Ethernet, etc. Since PCShare is compatible with EtherShare, Windows users can share network printers and files with Mac and UNIX users, too.


Portable Document Format. File format developed by Adobe Systems, Inc. PDF files were originally designed for online reading on all platforms.


The PICT file format is a native classic Mac OS image format.


Industry standard page-description language invented by Adobe and introduced in 1985 for printing documents that integrate text, graphics, images, and color.

PostScript fonts

In PostScript font files, the character information is given in PostScript code. PostScript printers require PostScript fonts or some sort of software that is able to transform non-PostScript fonts. For detailed information about the “font business”, please read refer to A “About fonts”.


PostScript Printer Description. A file format developed by Adobe Systems, Inc. PPD files contain information enabling software to produce the best results possible for each type of designated printer.

Rendering intent

The approach taken when a Color Management Module (CMM) maps or translates the colors of a source device to the gamut of a destination device. Each profile supports different rendering intents. Changing the rendering intent may lead to a different output result, even though you did not change the profile.


The dots per inch (dpi) value of an image indicates its resolution. The dpi value of a given device (scanner, printer, etc.) defines its resolution capacity. Very clear and sharp images require input/output devices with a high resolution (about 300 dpi or more). Monitor resolutions usually range from 72 to 100 dpi.


Screens and monitors produce colors by means of Red, Green and Blue light (RGB). The light intensities make up a given color. Scanners also work with RGB colors. They read the amounts of red, green, and blue light that are reflected from an image (or transmitted if you scan transparent images). RGB images contain three components per pixel, namely a specific amount of red, green, and blue.


Raster Image Processor. Converts vector data (e.g. PostScript) to raster image pixel data. The RIP may be either an external unit or part of the output device itself. A PostScript laser printer for example contains its RIP.


Run-Length Encoding. Mode of compression that saves repetitive patterns only once and adds the number of repetitions. RLE is a lossless compression.

Root directory

The top-most directory on a UNIX computer is called the “root” directory. If you are logged in as “root”, you can access all other directories and subdirectories on the system.


Set of programs which manage print jobs. A spooler acts as a buffer for the files that have been sent to an output device. In this documentation, “printer queue” may be used as a synonym for “spooler”.

Spot color

Exactly defined full tone color. Spot colors are printed on their own separation plates when separations are specified.


Specifications for Web Offset Publications. US standards for color separation and color printing.


Tagged Image File Format. Standard graphics file format for files that are to be exchanged among several applications and environments, including Mac, Windows, and UNIX.

TrueType font

TrueType is an outline font standard developed by Apple and Microsoft in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. It has become the most common format for fonts on both the Mac OS and Microsoft Windows operating systems.For detailed information about the “font business”, please refer to A “About fonts”.


WebShare is a high-performance HELIOS file server which enables fast and secure real time file access via any web browser. Since WebShare is compatible with PCShare and EtherShare, web users can share network files with Mac, Windows, and UNIX users, too.

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HELIOS Manuals September 10, 2020