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Bronx Community College office tel: (718) 289-5341 Prof. Roni Ben-Nun |
Glossary of Terms Raster Graphics: digital images created or captured (by scanning) as a set of samples of a given space. A raster is a grid of x and y coordinates on a display space. A raster image file identifies which of these coordinates to illuminate in monochrome or color values. The raster file is sometimes referred to as a bitmap because it contains information that is directly mapped to the display grid. A raster file is usually larger than a vector graphics image file. Vector Graphics: the creation of digital images through a sequence of commands or mathematical statements that place lines and shapes in a given two-dimensional or three-dimensional space. In physics, a vector is a representation of both a quantity and a direction at the same time. In vector graphics, the file that results from a graphic artist's work is created and saved as a sequence of vector statements. For example, instead of containing a bit in the file for each bit of a line drawing, a vector graphic file describes a series of points to be connected. One result is a much smaller file. Pixel (Picture Element): a pixel is a tiny dot of light on the monitor. It is the smallest part of every image you see on the monitor. The color of a pixel is partly determined by how many bits (on/off units) are used to store the pixel. bit (Binary Digit): a bit is an electronic signal, which is either on (1) or off (0). It is the smallest unit of information the computer uses. Computers use the binary system to work with data. All data is stored in binary code as 1's and 0's (bits). A bit might be called the "on/off" unit of information. byte: byte is a group of 8 bits, strung together. Each byte (8 bits) means something to the computer. The byte "01000001" means the capital letter A. The byte "01000010" means the capital letter B. bytes are arranged in units of K, MB, GB (kilobyte = 1000 bytes, megabyte = 1 million bytes, gigabyte = 1 billion bytes) Files and Formats A file is an entity of data available to users (including the system itself and its application programs) that is capable of being manipulated as a unit. The file must have a unique name within its own directory. Files with given formats are described by giving them a particular file name suffix (file name extension.) In general, the suffixes tend to be as descriptive of the formats as they can within the limits of the number of characters allowed for suffixes by the operating system. Conventionally, the extension is separated by a period from the name and contains three or four letters that identify the format. A file format is the layout of a file in terms of how the data is organized. A program that uses a file must be able to recognize and possibly access data within the file. For example, the program that we call a Web browser is able to process and display a file in the HTML format so that it appears as a Web page, but it cannot display a Microsoft's Excel file. A program that uses or recognizes a particular file format may or may not care whether the file has the appropriate extension name since it can actually examine the bits in the file to see whether the format (layout) is one it recognizes. There are as many different file formats as there are different programs to process the files. Examples of more common file formats: Word documents (.doc) JPEG (Joint Photographic Experts Group) a term for image files produced by using a JPEG standard, using a range of compression algorithms. The highest quality results in the largest file, you can make a trade-off between image quality and file size. GIF (Graphics Interchange Format) pronounced DJIF or GIF with a hard G stands for and is one of the two most common file formats for graphic images on the World Wide Web. The LZW compression algorithm used in the GIF format is owned by Unisys, and companies that make products that exploit the algorithm need to license its use from Unisys. PNG (Portable Network Graphics format) A patent-free replacement for the GIF, the, developed by an Internet committee and supported by all major browsers. |
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