The importance of an attractive and useful graphical display of information is fundamental to scientific programming. Just imagine the difference between seeing a graph of this week's stock market activity, and seeing a list of several pages of numbers describing the same activity. The former can be surveyed in a glance; the latter requires considerable study. The same principle applies to the display of results in bioinformatics. Of course, sometimes you need the raw data; but very often what you need is the overview that a good graphic can provide.
Although there are many programming systems to produce graphics, the most popular are those that can be displayed via web browsers. This chapter builds on what you learned in Chapter 7 by showing you how to add graphics to your display of scientific results on a web page.
My vehicle of choice for displaying scientific data is the GD.pm module, which allows you to produce images in the standard graphics formats PNG (Portable Network Graphics) and JPEG (Joint Pictures Expert Group), among others. I'll also briefly mention the graphics packages ImageMagick and Gimp, two more full-featured graphics creation and manipulation packages.
GD.pm is an interface to the gd graphics library written in the C programming language by Thomas Boutell. The gd graphics library is fairly basic; it's fast, it handles text and various kinds of lines and space filling by means of its various functions, and it is easy to program elements such as graphs.
The main reason for its success, however, based on those important technical reasons, is that it makes it possible to produce nice-looking graphics from your web site on-the-fly, in immediate response to a request from a user submitting a form.