Images, by George Rogers Posted 07/16/01

Relevant images, animations and video clips can add significantly to the information content of a web page. They also add time to the authoring process and can increase the download time of web pages. Avoid large graphics whenever possible. Notify users of large graphics or multimedia files, and let the user choose whether or not to view these large files. It is common practice to put small thumbnail images on the web pages that are linked to the full size graphical image. Avoid using many small images. The way computers retrieve web documents requires that a separate connection to a web server be initiated for each image. The time involved in negotiating this connection may actually be longer than the time involved in retrieving the image itself.

Images can be scanned and saved in any of the graphics formats that can be read by Microsoft Photo Editor (the enterprise standard), Adobe Photoshop or another graphic editing tool. Images can be manipulated and converted to one of the formats (GIF or JPG) required by HTML. The JPG format is better for photographs, whereas the (GIF) format is better for graphs and charts.

It is preferable to reference (thus re-use) images within a web site instead of creating new ones. You can use a small set of navigational icons that appear on every page on your web site. To do this, place the commonly used images in a directory and point all references to these images to the same location. This is preferred over copying the common images to each sub-directory.

Being able to produce high quality, but low file-size images is critical to an efficient web page. Knowledge of image scanning, image processing and computer-based drawing and illustration is highly recommended for people who are doing any significant amount of work with web graphics.

Image File Format - *.gif, *.jpg
In general, use the GIF format for general graphics and JPG for photographs. JPGS produces larger compressed files of photographic content, whereas GIF does a better job with illustrations or images that contains large areas of the same color. Specialized images, photographs and illustrations that are specific to a particular web page must be converted to the appropriate web format (GIF or JPG). Hard copy images also can be scanned into the computer and saved to one of the two graphic formats.

Applications such as Microsoft Photo Editor and Adobe Photoshop can enhance, modify, reformat, re-color, and resize scanned images, but requires some experience with image processing.

George J. Rogers
Web Site Content Coordinator
The University of Texas Health Science Center at Houston
713-500-3506