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Glossary

by Collin County Community College

Alpha Channel: An eight bit grayscale channel within some image processing software programs which is used for masking objects, making them transparent or adding specific color instructions.

Anti-Aliasing: The process of elimination of jagged or-"stair stepped" pixel edges or single pixels by a software algorithm, which blends the contrasting colors and shapes.

Binary: The basis for all digital computer information. Relates to the coding of data in terms of either a 1 or 0.

Bit: A shortened form of the term "binary digit," the smallest unit of information that can be stored in a computer. One digit of binary information can be either a mark or a space.

Bit Depth: A measure of a computer monitor's ability to display different colors at the same time. While a monitor with a bit depth of 1 can only display monochrome information, a monitor with a bit depth of 4 can display 16 colors; an 8-bit monitor can display 256 colors and a 24-bit monitor can display 16.7 million colors. A 32-bit monitor has an additional 8-bits for transparency effects or masking as in the case of an Alpha channel.

Bitmap: A pixel-by-pixel description of an image. Each pixel is a separate element. Also referred to as a raster image.

Bitmapped: An image, which is formed by a collection of square pixels in a rectangular format. The more bits per pixel the smoother the final image will be.

Byte: The computer standard of measure for file size, which is made up of 8-bits of information. One megabyte is 1,024 kilobytes. One gigabyte is 1,024 megabytes or about one million bytes. One kilobyte is 1,024 bytes.

Cache: Storage within the computer, which processes data very quickly. Often in RAM or can be a supplemental board. Increases operating speed and efficiency.

Calibration: The process of matching a monitor's color to print devices such as digital printers, ink-jet printers and offset printers.

CGI (Common Gateway Interface) script: An application that the server runs at specific times. For example, when a visitor connects to a server, the server might open a CGI script that displays a form the visitor fills out, and then sends the data to a storage area.

CMYK: Cyan, Magenta, Yellow, and Black -- The four process colors used in the printing industry, as in offset lithography.

Dither: The process of simulating color by a combination of small dots of primary colors which, when viewed, appear to mix and form the desired color. Very useful for the Web to correct GIF image output.

Domain type: The suffix of a Web site that identifies the type of content the Web site contains or what kind of organization the site is associated with (such as "com" for commercial, "edu" for education, "gov" for government, and "org" for a nonprofit organization).

DOT:
1. A Halftone dot (used in color separations). Halftone dots are often confused with pixels but the two are not related. Pixels have fixed size but variable density. Halftone dots have fixed density but variable size. This gives the illusion of a continuous-tone image when viewed from a distance. There is no fixed relationship between the number of pixels and the number of halftone dots per inch, but a halftone dot can resolve detail smaller than itself (by varying its shape), so for best detail there should be at least twice as many pixels per-inch as halftone dots.

2. A pixel in an input scanner or continuous-tone output device (e.g., dye sublimation printer). Scanner resolution is sometimes quoted in "DPI"(Dots Per Inch) but this can be misleading because here the word "dot" really means "pixel." When referring to a continuous tone scanner, "DPI" should be changed to "PPI" (Points Per Inch or Pixel Per Inch) or even to "LPI"(Lines Per Inch) to avoid confusion.

DPI: Dots Per Inch - A method for measuring the resolution of printers, imagesetters and other output devices.

EPS: Encapsulated Postscript - A file format standard established by Adobe for outputting digital images to Postscript output devices. Actually a simulation via a bitmapped image which approximates the final look of the Postscript image - when finally printed on an appropriate Postscript printer. Designed to allow the user to "preview" the image on the computer monitor.

Gamma: The way in which dark or light shades are measured in a photographic image. The measure of the image contrast, changing the midtone placement rather than the endpoints.

Gamut: The range of colors, which are available in a color system. If your color is out of gamut range, then it may not print or view correctly.

Grayscale: In black and white photography the highest bit depth mode which contains 256 shades of gray. Each pixel can be any one of values from zero to 255.

HTML (Hypertext Markup Language): A method for preparing text files so they can display content and link to other files on the World Wide Web.

Internet: The massive global network of interconnected computers and communications hardware and software that links World Wide Web sites and other services, such as e-mail, discussion groups, and FTP servers.

Internet service provider (ISP): A company that provides direct access to the Internet. The ISP usually has fast, dedicated connections to Internet services and multiple modems to which individual users connect over phone lines. When you establish an account with an ISP, the company provides the information and basic software you need to set up your computer for Internet access.

Interpolate: A process for estimation the difference between two known values. Resizing-up by considering the individual pixel and the surrounding area of pixels. Interpolation averages existing pixels to create new pixels. Takes longer than replication. Can soften the image definition and make it blurry.

Intranet: A network-based collection of Web servers and sites usually located within one company or other organization.

IP address: IP is short for Internet Protocol, a way of specifying how information is transferred across computer networks. The IP address, which identifies a specific computer, consists of a 4- to 12-digit number separated into four sections by periods (for example, 130.43.2.2).

JPEG: Joint Photographic Experts Group - A file format designed to standardize compression of digital computer images. Repeated use can degrade an image; the term "lossy compression" is applicable.

LAN: Local Area Network - A method for connecting personal computers together so they may share information and use of peripherals.

MIME type: Information associated with a file on a Web server. The MIME type tells the server, and the Web browsers of any connected users, what the file type of the file is, and which application to use to open the file. (MIME is an acronym for Multipurpose Internet Mail Extension.)

Multisync: A type of computer monitor, which is capable of adjusting to several different video signals.

Network: An assembly of several processing units interfaced together. (A network, by definition, must have computers linked together.)

NTSC: National Television Standards Committee.

Non-Lossy: A compression scheme, which does not allow the loss of any data during file compression. (Loss-less).

PICT/PICT2: Original generic file format for encoding illustrations on a Macintosh platform.

Pixel: The smallest unit of digital information. Think of it as a dot or grain, which contains information about the color or brightness value of the area of the picture it represents.

Postscript: A page description language created by Adobe.

PPI: Pixels Per Inch - The measure of resolution on the monitor or output device.

Raster: A displayed bitmap, a raster is essentially a grid of horizontal lines, which make up the picture on the screen.

Rasterization: A way to convert the curves in type and illustrations (vector-based graphics) into a pattern of dots which can be displayed on a raster based screen or print device.

Resolution: The number of dots per inch on the laser printed page or the computer monitor's screen. The number of pixels per unit of measurement.

Image Resolution: Total number of pixels of a particular image. Device Resolution - Determines output resolution. Example: monitor resolution = 72 or 80 ppi (Web graphics are set to 72 ppi, and print graphics are set to 266 or 300 ppi)

RGB: Red, Green, Blue - Additive color primaries Red, Green, and Blue, used in video tubes, as contrasted to the Subtractive primaries, Yellow, Magenta, and Cyan, used in printing. A color encoding system in which colors are expressed by three values, one each for red, green, and blue. This is directly compatible to a color photograph, in which the cyan, magenta and yellow layers are sensitive to red, green, and blue, respectively, in the original scene. Due to limitations in printing inks, printers must add a redundant black channel to increase contrast (see CYMK).

RIP: Raster Image Processor - The device that converts images in vector or line and curve form into raster or bitmap form.

Sampling: Sampling, re-sampling, scaling, up-sampling, down-sampling, and resizing up or down . . . terms used for increasing or decreasing the number of pixels in an image. Resizing down is easier to accomplish as existing pixels are simply discarded.

Scratch Disk: The disk used by Photoshop to replace physical RAM. This is defined in Photoshop's preferences. To work best the program needs free space on the scratch disk equal to about 4 times your file size. If you do not have this much free space you may get an inadequate memory message while editing your picture. Normally it is best to either have a very large hard drive to work with or have a separate disc for use in image editing.

Separations: The result of breaking a color image into four components that allow proper amounts of cyan, magenta, yellow, and black ink to be applied to recreate the colors on the printing press.

Services Bureau: An organization, which is set up to provide for the needs of computer users who will take their images to the printed page.

TCP/IP network connection: Abbreviation for Transfer Control Protocol/Internet Protocol, a way of specifying how information is transferred over the Internet (by means of a network connection).

TIFF: Tagged Image File Format - A standard format in which scanned images are saved for use in graphic applications. This format is compatible with both Mac and PC.

Unsharp Masking: A procedure for increasing the apparent detail of an image performed either by the input scanner or by computer processing.

URL (Uniform Resource Locator): The "address" or location of a Web site or other Internet service.

Vector: Lines or curves, which make up the page in a computer image. A set of computer instructions determining the creation of geometric shapes (Postscript file) as opposed to images made up of pixels, as in bitmapped graphics.

Vector Image: An image system that uses basic geometric shapes, like rectangles, lines, circles, ellipses and polygons, to create a graphic image. The vector image usually contains very little data, like the starting point (pixel) of the object, what kind of object it is, its size, and color. When the image is rasterized, the vector information is converted into a bitmap using a RIP (Raster Image Processor). Rescaling can be performed with greater accuracy than with raster data. Also called "object oriented." Once a vector image has been rasterized, it is best not to scale it more than 5% to 10% up or down.

WYSIWYG: What You See Is What You Get - A desktop computer system feature that allows the user to preview to some degree the final output to the printed page.

 

Article posted with permission from:
Art Space Design