Bitmaps / Vector Graphics
Image files can be either scalable vector graphics or bitmaps, both of which have their advantages and disadvantages.
A bitmap is an image which is made up of tiny squares of colour. The arrangement of these tiny coloured squares produce the effect of an image. This is a good method of reproducing 'continuous tone' images, such as photographs.
The amount of detail that can be seen in a picture depends on the resolution of the image; how many times per inch these squares or pixels occur. 300 times per inch is what is needed for good quality reproduction on a commercial printing press, and 72 pixels per inch for monitor display.
Bitmaps have two disadvantages. In terms of the amount of digital storage, bitmaps are memory intensive, and the higher the resolution, the larger the file size.
The other disadvantage with bitmaps is when an image is enlarged, the individual coloured squares become visible and the illusion of a smooth image is lost to the viewer. This 'pixelation' makes the image look coarse.
Scalable vector graphics are very different from bitmaps. Vectors describe the shape of an object as a series of points connected by curved or straight lines, represented as a mathematical formula. These lines may have a thickness or stroke assigned to them, and the object they create can be filled with colour.
The advantages of using vector graphics are; a small file size and the ability to scale the image to any size without loss of quality; see the image above. They are ideal for logo designs, as they can be printed very small on business cards or printed large on a billboard poster.
Vector graphics, however, cannot reproduce 'continuous tone' photographic images like bitmaps.