Unit 54 Digital Graphics for print

  Understand graphic formats and application 

Definitions: 


Raster - A rectangular pattern of parallel scanning lines followed by the electron beam on a television screen or computer monitor. A raster image is made of up pixels, each a different colour, arranged to display an image. A bitmap, a single-bit raster, corresponds bit-for-bit with an image displayed on a screen, generally in the same format used for storage in the display's video memory, or maybe as a device-independent bitmap. A raster is technically characterized by the width and height of the image in pixels and by the number of bits per pixel (or colour depth, which determines the number of colors it can represent).^[

Vector - A vector image is made up of paths, each with a mathematical formula (vector) that tells the path how it is shaped and what colour it is bordered with or filled by.One of the first uses of vector graphic displays was the US SAGE air defense system. Vector graphics systems were only retired from U.S. en route air traffic control in 1999, and are likely still in use in military and specialised systems. Vector graphics were also used on the TX-2 at the MIT Lincoln Laboratory by computer graphics pioneer Ivan Sutherland to run his program Sketchpad in 1963.

Metafiles  - A piece of graphical information stored in a format that can be exchanged between different systems or software.Microsoft uses this term for its Windows Metafile (WMF) format. A WMF file contains a sequence of graphical-device-interface (GDI) function calls ("commands" to the Windows operating system ) that results in the presentation of a graphic image. Some of the function calls are equivalent to vector graphics statements and others identify stored bitmap or literal specifications of which bits to illuminate ( raster graphics images). 

File extensions  - A file extension or file name extension is the ending of a file that helps identify the type of file in operating systems such as Microsoft Windows. ... For example, the file name "myfile.txt" has an extension of ".txt", which is a file name extension associated with text files. Computer files have specific characteristics which depend on the software that created them. If you try to open a file using the wrong program, it will fail to open or sometimes even crash the program. The last part of the file name is used to indicate the type of file so the computer can open the correct program when you want to use the file.

In the early days of the personal computer, file names consisted of up to seven characters followed by a file extension consisting of a full stop and three characters. But since 1995, file names can be much longer and the main part of the name can include full stops. So now the last full stop in the name is considered to mark the start of the file extension.