One of the most common misunderstandings among both clients, and unfortunately many designers, is the difference between Vector and Bitmap (also known as Raster) graphics.

BITMAP or RASTER

Bitmap graphics are the most common graphic format in use on the web and, indeed, on the computer and every single graphic seen on the web is a Bitmap.

Bitmap graphics are composed of pixels, each of which contains specific color information. A pixel is minutely small; a single image may be composed of hundreds of thousands of individual pixels. Even so, when enlarged, a bitmap image will pixelate (show the square pixels from which it is made,) if it does not have enough resolution for the intended purpose.

VECTOR

If we consider Bitmap graphics as being stored in a literal fashion, then Vector Graphics, stored representatively, are their opposites.

Vector graphics are mathematical creations. For this reason, the programs that are used to create them save instructions on how the image should be drawn, rather than how it looks. This is the key difference between the two types of graphics. Because the computer has a description of how the image should look, it can be redrawn at any size, in any position, without losing any quality. A vector graphic resized to 5 times its original dimensions is simply reproduced, exactly, at the new size. It can also be freely manipulated without losing coherence, like a rubber band that can be stretched an infinite number of ways.

When designing art to be printed on a press all logos, illustrations, drawings and written type need to be represented with vector graphics for sharpness and clarity. If there are photo-quality backgrounds or other photographic images, they can be placed into the vector illustration and will print best when the resolution of the image (bitmap) is at least 300 dpi (dots per inch.)

If a Bitmap graphic is opened with or pasted into a Vector editor, does it automatically become Vector?
Once a Bitmap graphic, always a Bitmap graphic. Although most Vector applications are able to display Bitmap images as embedded objects (and many applications even include a limited set of tools to manipulate them) their inherant format does not change. The only way to convert a Bitmap image to a Vector image is to trace the image using either a manual process or automatic program. The tracing proccess attempts to duplicate the shapes of a Bitmap image using Vector lines and curves. When Vector graphics are pasted or imported into Bitmap editors, however, the opposite is true. The editor converts the vector image to Bitmap as soon as it is brought in. Once a Vector image is converted to Bitmap, there is no way to return to the original state. For this reason, Designers keep copies of the original vector artwork when converting an image to a bitmap file format.

What are some common Vector editors and file formats?
Adobe Illustrator, Corel DRAW!, Macromedia Freehand, and Macromedia Flash are the predominate editors on the market. Common universal file formats include .eps and .wmf and .svg. Unlike Bitmap graphics, it is far more likely to see Vector files delivered in formats unique to the programs which created them. If you are using anything other than Adobe Illustrator, save the file as an .eps file prior to submission.