There are basically two ways of representing visual data on a computer: through dots and through geometry. The method using dots, in which each pixel is told where to go, is sometimes known as bitmap imaging, and more commonly known as raster graphics. The method using geometrical formulas is known as vector or vectorized graphics.
Historically, vectorized images were frequently used because they required much less memory than raster images. Most of the oldest graphical computers used graphics that were characterized by long arcs, circles, and other simple geometrical shapes, because they could be represented with only a few lines of mathematics, rather than a detailed description of where each pixel had to appear. As computers advanced and memory became less of an issue, vectorized images became less commonly used in most applications, where they were replaced by raster images. Vectorized graphics still remain, however, and are seeing something of a resurgence in popularity, for a number of reasons.
Vectorized images describe every aspect of their shape in terms of a mathematical formula. To see how beneficial this can be, imagine a simple shape, such as a circle. In a raster image, a circle that is 100 pixels wide will have to store where each of the pixels in that 1,000 pixel area is placed. If one were to zoom in on that image, one would start to see pixelization, since only those 1,000 pixels were described.
By contrast, on a vectorized image, a simple mathematical formula would describe the radius of the circle and the fact that it is a true circle, and the processor could calculate the rest. Not only is this a lot less information to deal with, but if one were to zoom in on the image, it would continue to have a smooth line, since the processor would just keep calculating the arc of the circle. This allows vectorized images to be manipulated much more easily – grown or shrunk, twisted and bent – without any distortion or loss of quality. It also means that higher-resolution monitors will display the vectorized images as higher-resolution graphics, while a raster graphic has a set maximum resolution at which it can be viewed, beyond which point no increase is noticeable.
Vectorized images are commonly used in computer assisted design, in many rendered images for movie special effects, and increasingly for computer animation. The popular Flash format makes use of vectorized images, allowing a much higher resolution in much smaller files than traditional raster graphics, making the images ideal for Internet applications and movies.
A constantly evolving field of computer intelligence is automated raster to vector conversion. Many programs attempt to automate the process of transforming a raster graphic – such as a painting or photograph – into a vectorized version, which can then be more easily manipulated, and in many cases may be much smaller in file size. Many vector-image programs, such as Freehand, include a Trace tool that automates this process, and a number of specialized applications exist, each with its own pros and cons.