Creating JPEGs (Web Design in a Nutshell, 2nd Edition)

20.5. Creating JPEGs

Because JPEG is a standard file format, it is supported by all the popular graphics tools. Adobe Photoshop/ImageReady, JASC Paint Shop Pro, and Macromedia Fireworks all provide similar options for saving JPEGs.

All of these products allow you to set the quality/compression level and save images in Progressive JPEG format. In Paint Shop Pro and Photoshop 5.0 and earlier, select "Save As" from the File menu and select JPEG from the available file formats. Photoshop Versions 5.5 and higher (including ImageReady) and Fireworks provide more advanced optimization options, side-by-side previews of the image and resulting file sizes, and an export function that preserves the original image.

There are also plug-in utilities especially for JPEG creation, such as ProJPEG from Boxtop Software (http://www.boxtopsoft.com) and HVS JPEG 2.1 from Digital Frontiers (http://www.digfrontiers.com). These plug-ins work with all of the programs mentioned here.

Regardless of the tool you use, the following guidelines apply:

Make sure your file is in RGB or grayscale format. You can apply JPEG compression to CMYK files in some applications, but these files are not compatible with web browsers.
Layered images must be flattened before they can be saved as a JPEG. Photoshop 5.5+, ImageReady, and Fireworks allow you to export flattened JPEG images while preserving the layered original.
Name your file with the suffix .jpg or .jpeg. This is necessary for the browser to recognize it as a readable JPEG file type.