There are very many digital image formats. Some of tyhe more popular ones and their particular useful purpose are listed below: TIFF files are lossless but require large files for storage GIF files are lossless and used primarily for web page graphics JPG files are lossy the most common with varying quality, 0=Low 12=High PNG files are JPG files without losing pixel data Many others less popular types mostly proprietary such as WMF, RCL, ECL, DWG etc. Lossless means that is when they are reviewed there is no loss of picture detail and the file has all of its original pixels intact. Some losses occur due to inability of these formats to store colour in high resolution, but it is a very small loss.
JPG files are lossy. When compressing a file to JPG format, the software will change some of the detailed information in the picture to allow for a smaller picture size. The compression/decompression algorithm is quite mathematical and part of this process loses data due to rounding off of numbers. When you save a picture in .jpg format a complex formula (algorithm) is applied which selects and discards varying amounts of "unnecessary" electronic information. This effectively compresses the picture file (by up to and in excess of 20:1) thus requiring considerably less storage space. When the file is "opened" again, an approximation of the missing bits is provided by the algorithm and inserted in the "holes" in the picture, which returns to its original dimensions although with the loss of varying amounts of quality (hence: .jpg's are "lossy" files). Nevertheless, pictures using the .jpg format look realistic since all of the computer's 16+ million possible colours can be used to make up the picture. Most digital cameras produce JPG formatted images. If you wish to store photos and preserve storage space, use the JPG format at a low compression ratio (10-12). If picture quality is not an issue (as in document storage) , store these in higher compression modes (1-9)
If you have the storage space and wish to store the finest detail that the eye cannot see, use the TIFF GIF or PNG format.