graphic file definitions

There are two main file formats used in typical graphic design -

Bitmap Graphics
Paint and image-editing software, such as Adobe Photoshop or Corel Photo-Paint, generate bitmap images (also called raster images).
The images use a grid of small squares, known as pixels, to represent graphics. Each pixel in a bitmap image has a specific location and colour value assigned to it. For example, a windmill in a bitmap image is made up of a collection of pixels in that location, with each pixel part of a mosaic that gives the appearance of a windmill. When working with bitmap images, you edit pixels rather than objects or shapes.

Raster images are the most common electronic medium for continuous-tone images, such as photographs or images created in painting programs, because they can represent subtle gradations of shades and colour. Bitmap images are resolution-dependent. This means that they represent a fixed number of pixels. As a result, they can appear jagged and lose detail if they are scaled on-screen or if they are printed at a higher resolution than they were created for.

Vector Graphics
Drawing programs such as Adobe Illustrator or Corel Draw create vector graphics, made of lines and curves defined by mathematical objects called vectors. Vectors describe graphics according to their geometric characteristics. For example, a windmill drawn as a vector graphic is made up of a mathematical definition of shapes drawn with a certain height and width, set at a specific location, and filled with a specific colour. You can move, resize, or change the colour of the windmill without losing the quality of the graphic.

A vector graphic is resolution-independent - that is, it can be scaled to any size and printed on any output device at any resolution without losing its detail or clarity. As a result, vector graphics are the best choice for type (especially small type) and bold graphics that must retain crisp lines when scaled to various sizes - for example, logos.