JPEG file format

JPEG was made to store photographic images in short files. Photographic computer images used to produce very long files due to the high number of colors in them. The JPEG image format is a lossy compressing image format. Lossy means that the image will lose quality while you gain shorter file sizes. Depending on the software used to create the JPEG files, you will be required to select a quality level ('low' to 'excellent' in Photoshop) or a percentage value for compression (0% to 100% in XV on SGI workstations). JPEG stores RGB or CMYK images as described on page .

It takes some experience with images of different kinds to select the appropriate compression rate. If a photographic image is to be saved, there is usually no problem as long as there are more or less smooth contrasts. 'High' or sometimes even 'Medium' in Photoshop is sufficient, and the percentage values for other programs different from Photoshop usually use the range of 70% to 85%.

Two rules for working with JPEG are important:

1. Do not save your 'master image' as JPEG. If your design work is not yet finished, use your program's preferred image format. When all the design is done, save the JPEG file and keep a copy of the original file as well! The reason is that every time you save in JPEG, you lose a bit of quality. If you work on an image, loading and saving it multiple times, you lose quality every time.
2. Check your JPEG images after you saved them by loading them back into your application and comparing them to the original you saved them from! If your selected compression was too low, you will recognize intolerable losses of image details or blurring around high contrast areas.

To use JPEG images on the Web, their file names must end with '.jpg'.