The optimization process has two distinct sets of rules regarding resolution, color depth, color mode and file format, depending on whether your intended medium is print or electronic.
Use an image-editing program to downgrade a high-resolution image before importing it into your computer-based presentation. Hi-res images (300dpi or higher) are necessary only for print projects; 72dpi is usually fine for electronic applications.
Set the image's mode to correspond to your medium.
For print, convert it to CMYK. For electronic media, be sure the image is saved in the RGB mode.
Convert your images to the appropriate color depth for your project.
Color depth for both print and electronic media images varies from 1-bit to 24-bit, depending on the project. However, the general rule for presentation bitmap image files is that a file's color depth should match the display resolution of the computer that will be used to run the presentation. For example, if your presentation will be viewed on a system with an 8-bit color display, you'll want to use a program such as DeBabelizer to batch-convert all your images to an 8-bit color depth. If your presentation will be run on more than one computer, convert all your images so they're compatible with the lowest-resolution system.
Make sure your image file is in the proper format for the type of project.
Common file types for electronic media include PCX, BMP, GIF and JPEG; none of these are suitable for print. EPS and TIFF files are two of the most common print-file formats.
Christine Saucier is a free-lance graphic designer specializing in Web-site design, multimedia authoring and presentation development. She can be reached at firstname.lastname@example.org, www.tiac.net/users/sauc.