In computing, JPG /JEPG is a commonly used method of compression for photographic images. The name JPEG stands for Joint Photographic Experts Group, the name of the committee that created the standard. The group was organized in 1986, issuing a standard in 1992 which was approved in 1994 as ISO 10918-1. JPEG is distinct from MPEG (Moving Picture Experts Group) which produces compression schemes for video.
The JPEG standard specifies both the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, and the file format used to contain that stream. The compression method is usually lossy compression, meaning that some visual quality is lost in the process, although there are variations on the standard baseline JPEG which are lossless. There is also an interlaced "Progressive JPEG" format, in which data is compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed whilst downloading over a slow connection, allowing a reasonable preview before all the data has been retrieved. However, progressive JPEGs are not as widely supported.
The file format is known as 'JPEG Interchange Format', as specified in Annex B of the standard. This is often confused with the JPEG File Interchange Format (JFIF), a minimal version of the JPEG format that was deliberately simplified so that it could be widely implemented and thus become the de-facto standard. Most image editing software programs that write to a "JPEG file" are actually creating a file in JFIF format.
Image files that employ JPEG compression are commonly called "JPEG files". The most common file extension for this format is .jpg, though .jpeg, .jpe, .jfif and .jif are also used. It is also possible for JPEG data to be embedded in other file types, such as TIFF format images.
JPEG/JFIF is the format most used for storing and transmitting photographs on the World Wide Web. For this application, it is preferred to formats such as GIF, which has a limit of 256 distinct colors that is insufficient for color photographs, and PNG, which produces much larger image files for this type of image. The JPEG compression algorithm is not as well suited for line drawings and other textual or iconic graphics, and thus the PNG and GIF formats are preferred for these types of images.
