Raster graphics

In computer graphics, a raster graphics image is a dot matrix data structure, representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium. Raster images are stored in image files with varying formats.

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 color depth, which determines the number of colors it can represent).

The printing and prepress industries know raster graphics as contones (from "continuous tones"). The opposite to contones is "line work", usually implemented as vector graphics in digital systems.

The word "raster" has its origins in the Latin (a rake), which is derived from (to scrape). It originates from the raster scan of cathode ray tube (CRT) video monitors, which paint the image line by line by magnetically steering a focused electron beam. By association, it can also refer to a rectangular grid of pixels. The word rastrum is now used to refer to a device for drawing musical staff lines.

...
Wikipedia