Perl Graphics Programming

Creating Raster Images and Web Graphics

Part I covers raster image formats and several popular libraries for manipulating them. Since most people will be using these tools to generate graphics for the Web, this section is supplemented by Appendix A, which presents the standard ins and outs of creating CGI scripts that generate dynamic images. Appendix A also takes a look at the HTML tags that embed images in web pages.

In Chapter 1, the “black box” of the three predominant web graphics formats (GIF, JPEG, and PNG) is opened, explored, and accompanied by a discussion of web graphics concepts such as transparency, compression, interlacing, and color tables.

In Chapter 2, we discover the GD module, a collection of functions for reading, manipulating, and writing simple raster images. GD is great for CGI scripts and for building other modules (such as GD::Graph; see Chapter 4).

In Chapter 3, we are introduced to ImageMagick and its Perl interface. ImageMagick is a collection of functions and a transparent interface for reading and writing over 40 different graphics file formats. It is a great “Swiss army knife” for image conversions, scaling, cropping, and color management. It can handle file formats that contain multiple images in a single file such as GIF89a. ImageMagick is (of necessity) a bit bulky, and may not be suited for all CGI programming tasks, but it certainly can be used for a lot of them. This chapter is supplemented by Appendix C, a table of the various file format capabilities of ImageMagick.

In Chapter 4, we use GD::Graph to create graphs from data. GD::Graph is a Perl module that extends the GD module by offering a number of functions for creating eight types of graphs and charts. In the early days of the Web, almost all of the financial graphs or web server load graphs were generated by CGI scripts using GD::Graph (actually, its precursor, GIFGraph) to generate the images.

In Chapter 5, we learn how to use the Gimp-Perl module to create custom plug-ins for the GNU Image Manipulation Program. The Gimp is a poster child for the free software movement; it’s a platform (similar to Adobe’s Photoshop) for manipulating raster images. The Gimp has a sophisticated scripting interface (several, actually). In this chapter we use the Gimp-Perl interface to write Gimp plug-ins. Chapter 5 is supplemented by Appendix B, which provides a reference guide for the Gimp.