This Style Usage Guide predominately deals with graphic art that at some point existed as information on a computer as a file. The visual representation can be translated and stored in various formats. This chapter explains the differences, strengths and weakness of the two main ways that graphics are stored on electronic media: Vector and Raster.
Vector graphics (also called geometric modeling or object-oriented graphics) is the use of geometrical primitives such as points, lines, curves, and polygons, which are all based upon mathematical equations, to represent images in computer graphics. It is used by contrast to the term raster graphics, which is the representation of images as a collection of pixels (dots).
The main advantage of vector graphics is they are Scalable. Since they are based on mathematics the same information used to create an image the size of this paragraph can also be used to create the same image the size of an outdoor billboard. The main disadvantage is that images in this format are most often seen as line drawings or cartoons. For our purposes in the use of logos, vector graphics provide the best consistency and precision.
The following are some typical file types you will encounter with vector graphics. Here they are commonly identified by their file extension typically seen in a windows-based computer environment.
A raster graphics image, digital image, or bitmap, is a data file or structure representing a generally rectangular grid of pixels, or points of color, on a computer monitor, paper, or other display device. The color of each pixel is individually defined; images in the RGB color space, for instance, often consist of colored pixels defined by three bytes-one byte each for red, green and blue. Less colorful images require less information per pixel; for example, an image with only black and white pixels requires only a single bit for each pixel. Raster graphics are distinguished from vector graphics in that vector graphics represent an image through the use of geometric objects such as curves and polygons.
The main advantage for raster graphics is the superiority of photo-realistic image quality. More detailed visual information is stored in the way our eyes perceive the universe around us. The main disadvantage is in scaling these pictures, i.e. changing sizes. Downsizing, or making smaller is usually not a problem in visual presentation, but Upsizing, or making larger most often does not provide for visually appealing results. Also, files stored in this format can be very large. A magazine quality photograph can be several mega-bytes in size.
Picking the best image file to use combines a lot of choices. This Style Usage Guide has made the choices to provide you Adobe® Illustrator® CS2 native files as master files and the PNG file format for your raster graphics. We hope that this serves a majority of your needs, whether you are preparing a newsletter, print ad, poster, PowerPoint® presentation, video or web site. Good Luck and thank you for all you do!
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