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Understanding dynamic images
Most images that appear on Web pages come directly from a file on the server containing them in their final format. Some images, however, are generated on demand or served from a database of images where there are parameters included in the request from the browser to read the image. These parameters provide information to the image provider that may be used to select an image or to generate an image on demand. A common example is the generation of maps. A number of Internet sites provide maps, and these maps are dynamically generated based on URL query parameters.
GoLive provides general support for dynamic image providers, although not all features offered may work. However, GoLive offers built-in support for Adobe AlterCast, a dynamic image generator. Specific support for other image providers can be added using the GoLive extension mechanism. Also, you can check the Adobe GoLive Exchange Web site for extensions supporting image providers.
Here is what happens when a dynamic image is requested. On the Web page, the <img> tag includes a reference to the URL of the dynamic image provider. URL parameters are included that provide information needed to generate or select the image. When the page is loaded, the browser requests each of the referenced images, including images that may be constructed dynamically (the browser doesn't know if the image is dynamic or not). When the request for the dynamic image arrives at the server, it forwards the request to the image provider. (This is based on the URL or file type; the image provider must be installed and registered with the Web server to support this.) The image provider generates the image and returns it to the browser. The browser displays it in the viewer's browser along with the rest of the Web page.
There may be important performance considerations when using dynamic images. The amount of time it takes to generate a dynamic image will depend on the provider and the server environment. This amount of time may be significant in the viewer's perception of Web page load time. You should be sure to consider this in the design of your Web page and site.
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