JPEG (Jay-Peg) stands for Joint Photographers Experts Group (file extension = .JPG). Experts joined together and agreed on a method of compressing full-size digital images such as BMP (bit-map) and TIFF (Tag Image File Format – file extension = .TIF).

BMP and TIFF are very high quality files, but take up a great amount of space when stored. They are usually too large (file size) to send by e-mail. TIFF images fill a camera memory card very quickly. The compressed format (.JPG) is more commonly used with cameras.

WHAT IS A JPEG? In an attempt to simplify, imagine a fresh apple, full size and water content. It is heavy and takes up a lot of room. You cannot snail-mail it with one stamp. Then imagine the apple completely dehydrated and flattened. Now it can be mailed with one stamp. At the destination, it is restored by soaking it overnight in water. You get a reconstitution of the original apple (work with me here, OK?). J

The process of compressing a full-size digital image results in a .JPG file that is much smaller than the original (can be one-tenth in size). .JPG is only used for storage and is not itself an "image". The .JPG file is a ‘recipe’ for restoring the original full-size file. A .JPG file viewed on the monitor is restored to a full-size image. If you at that point could save it as a .BMP, it would be a full-size image file again (reconstituted apple).

COMPARISON OF BMP & JPG: The cat with the RED border is a small .BMP file (200 x 200 pixels). The cat with the BLUE border is the same BMP image that was saved as a .JPG file. You may not be able to see any difference between the original and the compressed image( now restored to full size). However, when an image file is compressed (i.e. to .JPG), some quality is lost. If highly compressed, degradation in quality can be seen and would show up in printing. Programs that provide JPEG compression allow a selection of quality versus file size. The .JPG shown on the right was saved at quality 5 of 12 in Photoshop.

200 x 200 pixel .BMP (118KB file size)––––200 x 200 pixel .JPG (18KB file size)

NOTE: Some believe that if you open a .JPG image then just close it again, there is degradation. This is false, because the original file is not affected unless the opened .JPG is saved over the original file, using the same file name. Note that if you create a new .JPG file by saving the opened file using a different name, this would indeed result in loss of quality in the new file, as it would undergo compression again. The degradation depends on the degree of compression.