Raster graphics

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Imagine the smiley face in the top left corner as an RGB bitmap image. When zoomed in, it might look like the big smiley face to the right. Every square stands for a pixel. Zooming in further, one can analyze three individual pixels, with their colors constructed by adding the values for red, green and blue.

Raster graphics (or bitmaps) is one of two ways to do computer graphics. With raster graphics, images are modeled as a big collections of pixels. Usually they form a rectangle. Each pixel has special things, like color, or transparency. Raster images are used very often. Computer screens are made of a raster of points. That way, vector graphic images need to be rasterised. Images that are difficult to make as a vector, like photographs are often in the form of a raster image.

Many printers today use languages like Postscript or PCL. These languages are based on vectorized images, most of the time. To be printed, these images must first be translated into raster graphics. This is done by a component called Raster Image Processor. Most modern printers have raster image processors in the printer. Some printer use a special piece of software on the computer to do the rasterising.

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