There are a variety of ways to enhance a Web page with images, audio, video, and interactive or dynamic elements. By enhance we mean make a Web page more valuable and useful to our prospective readers. It is important to remember that adding elements to a Web page may in fact detract from the overall experience. Two issues to consider are the amount of time it will take to download and view a Web page, and whether the person viewing a Web page has the proper software and hardware installed to take advantage of the content you provide.

Images, animations, audio, and video can enhance a Web site if they’re used appropriately. Think about the person who will be viewing or accessing the Web page, and use these elements with the goal of providing a richer experience. There are several considerations and techniques that can help with this.

Some ways to minimize the time it takes to view Web pages with images are to:

• reduce the size and number of colors in an image
• use images more than once on related pages
• set the size of the image as an attribute of the <IMG ...> HTML tag
• save an image as an interlaced GIF or a progressively encoded JPEG
• display a two-color version of an image while the full-color image is loading

Animated GIFs, a common way to provide animations, are collections of images. Take special care to minimize the size of each.

Audio information is stored in one of several different file types. Each represents a different compression or playback scheme. Some file types need to be downloaded completely before they can be played. Another technology called streaming—it’s also used with video—downloads a portion of the file and starts playing the audio (or video) as portions of it are downloaded. Streaming file types and some others require that a plug-in be loaded first, before the file may be played. Plug-ins for popular file types are readily available, but needing one increases the amount of time before the file is played. There are two choices for giving access to audio on a Web site. One is to give a hyperlink to the audio file so that a person visiting the site may choose whether to access the file, and the other is to embed the audio file on a Web page. Audio files tend to be large, so the first option is often better for the visitor.

The considerations related to using video are similar to audio. There are different encoding and compression schemes including streaming video, the files are very large, and there are the same two ways to give access to video files.

There are some other ways to provide dynamic elements in Web pages. These are also used to produce interactive elements in a page or create Web pages as the result of user input. In this chapter we discuss Java, JavaScript, and CGI programs.

Programs written using Java can be distributed on the Internet and executed on several different types of computers. The programs are translated, using a Java compiler, into a format called byte codes. The byte codes can be executed on any computer with a Java interpreter, and the same byte codes are produced regardless of the type of computer used to develop the program. Java programs used on the Web are called applets. A Java applet is included in a Web page using the HTML tags <APPLET specifics about an individual applet> and </APPLET>. The programs are first written in Java and then compiled or translated to byte codes using a Java compiler. When a Web browser retrieves a page with the APPLET tag, the byte codes are sent to the computer viewing the Web page to be executed there.

Most Web browsers include an interpreter (part of the browser software) that will interpret and execute instructions written in a language called JavaScript. These instructions are part of the Web page. They aren’t compiled first, as is the case with Java programs. JavaScript includes ways, for example, to write instructions that respond to events that occur while a person is viewing a Web page. These events include opening or closing a Web page, moving the mouse over a region of a form, clicking on a button on a Web page, or selecting an item from a menu. A script could collect and verify input from a user before passing it back to a server or an applet.

CGI programs are programs that run or execute on a server, not the client, as is the case with Java and JavaScript. In a nutshell, a Web page (on a client system) through a form or an image tag references a CGI program. The input data for the program is taken from the Web page, the program processes the data, and the program may produce output as a Web page that is sent back to the client system.

If your Web presence provider gives access to CGI programs or if you use some of the free CGI services on the Web, you’ll get a copy of the HTML to use. Then you customize it as necessary to fit your application. In either case you need to know:

There are several sites on the Web that provide images, animations, sounds, video, Java applets, JavaScript programs, and CGI programs without charge. There are also many sites that can be helpful in working with different file types and learning how to use these elements in Web pages. It’s great to have all these resources available, and great to have so much to learn! Just remember that a person viewing your Web page is a visitor and you need to make sure their visit is pleasant and enriching for them.

Summary | Terms | Exercises | FYIs

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