JPEG

   The most commonly used digital image format is JPEG (Joint Photographic Experts Group). Universally compatible with browsers, viewers, and image editing software, it allows photographic images to be compressed by a factor 10 to 20 compared to the uncompressed original with very little visible loss in image quality. 
 
The Theory in a Nutshell
   In a nutshell, JPEG rearranges the image information into color and detail information, compressing color more than detail because our eyes are more sensitive to detail than to color, making the compression less visible to the naked eye. Secondly, it sorts the detail information into fine and coarse detail and discards the fine detail first because our eyes are more sensitive to coarse detail than to fine detail. This is achieved by combining several mathematical and compression methods which are beyond the scope of this glossary but explained in detail in 123di. 
 
A Practical Example 

   JPEG allows you to make a trade-off between image file size and image quality. JPEG compression divides the image in squares of 8 x 8 pixels which are compressed independently. Initially these squares manifest themselves through "hair" artifacts around the edges. Then, as you increase the compression, the squares themselves will become visible, as shown in the examples below, which are magnified by a factor 2.