JPEG (JPG)

In computing, JPEG (pronounced JAY-peg; IPA: /ˈdʒeɪpɛg/) 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 that 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 after receiving only a portion of the data. 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 Interchange Format that was deliberately simplified so that it could be widely implemented and thus become the de-facto standard.
The reason for this simplified version was that JPEG Interchange Format suffers from three shortcomings that prevent it from being easily understood and implemented:

  • Color Space definition
  • Component Sub-Sampling Registration definition
  • Pixel Aspect Ratio definition
In addition to JFIF, other standards have evolved to address these shortcomings, including 'Exchangeable image file format' (Exif) and ICC color profiles.
Image files that employ JPEG compression are commonly called "JPEG files". Most image editing software programs that write to a "JPEG file" are actually creating a file in JFIF format.[1]
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, JPEG/JFIF is far superior to GIF, which uses a palette with a maximum limit of 256 distinct colors (most color photographs contain many thousands of distinct colors). JPEG/JFIF is also preferred to PNG, which produces much larger image files for this type of image due to its lossless compression.
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.
The MIME media type for JPEG is image/jpeg (defined in RFC 1341).
DocFamily supports JPEG as an image format used in documents as well as an output format for documents.