Throughout this book we have seen many examples of CGI scripts generating dynamic output. However, in almost all cases, the output has been HTML. Certainly this is the most common format your scripts will generate. However, CGI scripts can actually generate any type of format, and in this chapter we will look at how we can dynamically generate images.
Generating images dynamically has many uses. One of the most common is to generate graphs. If you have a data source that is continually changing, such as the results of an online survey, a CGI script can generate a graph that presents a visual snapshot of this data.
There are also times when generating images dynamically makes less sense. It is much less efficient to generate an image dynamically than for your web server to serve the image from an image file. Thus, just because some of these tools allow you to generate really cool graphics dynamically doesn’t mean you must use them only in a dynamic context. Unless the images you generate are based upon data that changes, save the image to a static file and serve that instead.
This chapter presents a broad overview of the different tools available for generating dynamic images online, and includes references with each for finding more information. The goal of this chapter is to explain techniques for generating images dynamically and familiarize you with the most popular tools available to you. A full description of many of these tools along ...