Preparing images for publication on the Web or for distribution via email presents its own unique set of challenges. Because the majority of Internet users still depend on dial-up connections (as opposed to high-speed DSL or cable connections), an image's file size is of primary concern. Your image needs to be small enough to download quickly while retaining enough information to display the colors and details of your original image.
Photoshop Elements helps you accomplish this digital sleight-of-hand through a process called optimization. Optimization pares down and streamlines an image's display information based on variables that you select and control. By limiting the number of colors in an image, or by selectively discarding pixels that are less critical than others, Photoshop Elements simplifies an image and reduces its file size. Once an image has been simplified in this way, it is said to be optimized (Figure 10.1).
Figure 10.1. The original illustration of the Chinese fan (left) contains a great deal of detail and subtle gradations of tone and color. The optimized version (right) is greatly simplified and contains far less color and image information.
Photoshop Elements offers four file format options for optimizing an image: JPEG, GIF, PNG-8, and PNG-24. Generally speaking, JPEG and PNG-24 are most appropriate for images that contain subtle transitions of tone and color (like photographs), whereas GIF and PNG-8 are best for graphics or illustrations containing a lot of flat color or typography (Figure 10.2).
Figure 10.2. The photograph on the left, with its subtle and varied tones and color, is a good candidate for JPEG optimization, whereas the flat, bold colors and use of typography in the illustration on the right make it more appropriate for GIF optimization.