Recently I received a somewhat convoluted question from a reader who couldn’t get her graphics to look good. Without going into laborious detail, her problem basically came down to a lack of understanding about the difference between vector and bitmap artwork.
Many programs and people just use the term "picture" to refer to any type of graphic they insert in a document. However, when you are working with graphics, you need to take one fundamental difference into account. You need to know if your graphic is a bitmap or vector line art.
A bitmap graphic is the type of graphic you create if you scan or bring in an image from a digital camera. Programs such as Adobe Photoshop, Paint Shop Pro and even Windows Paint can create and modify bitmap graphics. Bitmaps are made up of a series of tiny dots called pixels that are sitting in a grid.
You often hear the term resolution in conjunction with bitmaps. The resolution is merely the number of pixels per inch in the image. A low resolution bitmap may be 72 pixels per inch (or dots per inch, which is abbreviated dpi). A higher resolution image may be 300 dpi. If you print out a low-resolution image on a newer laser printer, you may discover it gets fuzzy. Similarly, if you enlarge a bitmap, it also may lose quality and not be clean looking.
Unlike bitmaps, vector graphics don’t involve pixels at all. These type of graphics specify each object in a picture as a mathematical formula. Therefore, vector line art is considered "resolution independent." If you draw a square and enlarge the image later, the quality of your square won’t be affected when you print out the drawing. Programs such as Corel Draw and Adobe Illustrator are used to create and modify vector line art graphics. If you are creating logos or other illustrations, it’s best to save it in a vector format, so you can scale it to any size.
You can save your artwork in many different file formats. For example, line art can be saved as Windows Metafile (WMF), Adobe Illustrator (AI), Corel Draw (CDR), and other formats. Bitmaps are often saved as TIF, JPG, or GIF files.
In the case of the confused reader, her graphic was a flow chart. She was turning it into a bitmap, rather than leaving it as vector line art, and the results were ugly when she resized it. It’s more proof that understanding the difference between vector line art and bitmaps can avoid a lot of graphic frustration in the long run.