File Formats and File Size

The first thing you need to learn about preparing web graphics is the type of file format to use. There are two standard choices: GIF (Graphics Interchange Format) and JPEG (Joint Photographic Experts Group). There's also a third format known as PNG (Portable Network Graphics). It's actually been out for several years and promises to be the best choice of all three, but it has never really caught on. Use it if you like it, but be aware that there might still be a few folks out there whose software can't read PNG files.

The most important thing to remember, regardless of the file format you decide to use, is that the web has limited bandwidth. This means that if you create an absolutely beautiful image and it weighs in at something like 4MB, it will take forever to download on a 56K modem—better than 10 minutes. This is not to say that you can't create images with as large a file size as you want. I am just suggesting that few web surfers out there will have the patience to sit and wait while your 4MB image downloads. If you know that your primary audience is surfing from home with slower modems, you might want to keep your web page images under 30KB apiece—a size that a 56K modem can download in a comfortable 6 seconds. This is an area where the preview images in the Save for Web & Devices dialog box can be a big help. They let you decide how small you can save a file without sacrificing quality.

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