Part of the Multimedia and graphics glossary:

Also see frame , raster graphics , and raster image processor .

The term raster refers to the region of a cathode ray tube ( CRT ) or liquid crystal display ( LCD ) monitor that is capable of rendering images.

In a CRT, the raster is a sequence of horizontal lines that are scanned rapidly with an electron beam from left to right and top to bottom, in much the same way as a TV picture tube is scanned. However, there are certain differences. In general, the resolution is better in a computer CRT than in a TV picture tube. Also, a TV raster scan is interlaced , while the raster scan in a computer CRT is almost always non-interlaced . In a CRT, the raster is slightly smaller than the full screen size of the monitor. The height and width of the raster can be adjusted, as can the horizontal and vertical position. Other parameters such as pincushioning, horizontal linearity, and vertical linearity can be adjusted in some CRT monitors.

In an LCD, the raster (usually called a grid ) is scanned differently than in a CRT; image elements are displayed individually. The raster normally matches the screen monitor in size. But if low resolution is used (for example, 640x480 pixel s on an LCD intended for 800x600), the displayed image may fill only part of the screen. If high resolution is used (such as 1024x768 pixels on an LCD intended for 800x600), the displayed image may exceed the area of the screen, and scrolling will be necessary to view all portions of the raster.

This was last updated in September 2005
Posted by: Margaret Rouse

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