Raster graphics

Note: for the use of the term "raster" in radio regulation, see frequency raster

A raster graphics Suppose the smiley face in the top left corner is an RGB bitmap image. When zoomed in, it might look like the big smiley face to the right. Every square represents a pixel. Zoomed in further we see three pixels whose colors are constructed by adding the values for red, green and blue.

To illustrate the matter further - here's the letter "J":

Look closely at it... Take a magnifying glass to it if you like -- you won't get fried, although you may see some chromatic aberration at the edges of the magnifier. You see a "J", the computer sees something more like this, where '.' represents a zero and 'X' represents a one:

....X
....X
....X
....X
X...X
.XXX.

Where you see a zero, the computer instructs its video hardware to paint the current background colour. A one calls for the current foreground colour. Yes, it is actually a bit more complicated, but it all basically boils down to one bit or the other making a distinction between the colours of adjacent pixels, which together form an image. This is the basic principle behind drawing on a computer.

In 3D computer graphics, the concept of a flat raster of pixels is sometimes extended to a three dimensional volume of voxels. In this case, there is a regular grid in three dimensional space with a sample containing color information at each point in the grid. Although voxels are powerful abstractions for dealing with complex 3D shapes, they do have large memory requirements for storing a sizable array. Consequently, vector graphics are used more frequently than voxels for producing 3D imagery.

Raster graphics was first patented by Texas Instruments in the 1970s, and is now ubiquitous.

For practical information on using raster graphics:

Article based on bitmap (http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?bitmap) at FOLDOC (http://www.foldoc.org).

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