JPEG (Joint Photographic Experts Group) is a lossy compression technique for color pictures. Pronounced "jay-peg", JPEG is an ISO/IEC group of experts that creates and maintains standards for a suite of compression algorithm for computer image files.

JPEG standards help image files to be compressed to around five percent of their original size, though some details are lost during compression. The commonly used file extensions for th JPEG format are .jpg, .jpeg, .jfif, .or jpe.

The extension JPEG specifies only how an image is transformed into a stream of bytes. JFIF (JPEG File Interchange Format), another standard developed by the Independent JPEG Group, specifies how to create a file suitable for computer storage and transmission (like sending through the Internet) from a JPEG stream. There are also other JPEG-based file formats including JNG and the TIFF format which can carry JPEG data as well.

JPEG Image Formats

JPEG/JFIF is one of the most popular image formats used for storing and transmitting images on the Internet. The main reason behind this popularity is the extremely effective compression offered by the JPEG file formats. This compression enables people to quickly transmit (send or receive) image files over the Internet.

JPEG performs best on photographs and paintings of realistic scenes with smooth variations of color and tone. JPEG is not frequently used for charts, line drawings, and other iconic or textual graphics. This is because the compression method used by JPEG can distort these images. PNG (Portable Network Graphics) and GIF (Graphic Interchange Format) are used for these types of graphics. Since GIF has only eight bits per pixel, it is not well suited for color images. PNG can be used to losslessly store images; but the large size of PNG files makes it unsuitable for transmitting over the Internet.

JPEG Compression

JPEG is a lossy compression method performed using discrete cosine transformation, where some data from the original picture is lost. Though the amount of compression depends upon the original image, ratios of 10:1 to 20:1 do not typically cause noticeable loss in the original image.

In the JPEG compression method, compression is done by splitting the original image into minute pixel blocks, which are halved again and again to achieve the desired amount of compression. JPEG images can be created using software or hardware. JPEG compression hardware provides sufficient speed for realtime, on-the-fly compression. C-Cube Microsystems is credited with introducing the first JPEG chip.

When a JPEG file is created or an image is converted from another format to JPEG, the user must specify the desired quality of the image. If the user chooses to create the highest quality image possible, the file size will be large. If the user is willing to sacrifice image quality, the resulting JPEG file can be much smaller.