Since early 80's home computers, there was a very important decisive factor when computers where compared: which has the best graphics. Still in our days, the need of an ever better representation and manipulation of graphics on our computer screens is one of the driving forces behind the computer technology (Graphics hardware,England, N,Computer Graphics and Applications).
In computer applications graphics are represented digitally using vector or raster formats. The vector format uses points in space which may be connected with lines. We use vectors to represent graphics which are scalable and with well defined limits. Graphic and 3D design artists use software that handles complex vectors to design their artefacts, and GIS applications use vectors to represent discrete objects like rivers or create different layers of information overlaid to raster maps.
On the other hand, the raster format can represent heavily detailed images. Imagine a grid, where each cell - some may even call it pixel - contains a binary value with information regarding the color of the cell. A raster file is a series of such bits, with an initial header specifying the gird's dimensions.
Compression techniques have evolved to help the distribution of large raster files over the networks. Lossless formats like the 8-bit GIF uses indexes to hold pixel information and to recreate the image on the screen. Web designers can create complex backgrounds using small GIFs by programmatically repeating them on the web page. The lossy 24-bit JPEG format produces smaller file sizes by eliminating bits of information based on sophisticated algorithms and is widely used to store complex imagery such as photographs.
The 24-bit PNG format tackles both problems of large files and data loss by using indexes like the GIF. Is very useful for web-galleries when JPEG is used to create thumbnails but the user downloads a high quality PNG.
Source: Butterworth, R. & Dykes, J., Lecture 04: Graphical information.
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