Editing JPEG (section)

==JPEG files==
<!-- This section is targeted by the redirect [[JPEG Interchange Format]] -->

The [[file format]] known as "JPEG Interchange Format" (JIF) is specified in Annex B of the standard. However, this "pure" file format is rarely used, primarily because of the difficulty of programming encoders and decoders that fully implement all aspects of the standard and because of certain shortcomings of the standard:
* Color space definition
* Component sub-sampling registration
* Pixel aspect ratio definition.

Several additional standards have evolved to address these issues. The first of these, released in 1992, was the [[JPEG File Interchange Format]] (JFIF), followed in recent years by [[Exchangeable image file format]] (Exif) and [[International Color Consortium|ICC]] [[ICC Profile|color profiles]]. Both of these formats use the actual JIF byte layout, consisting of different ''markers'', but in addition, employ one of the JIF standard's extension points, namely the ''application markers'': JFIF uses APP0, while Exif uses APP1. Within these segments of the file that were left for future use in the JIF standard and are not read by it, these standards add specific metadata.

Thus, in some ways, JFIF is a cut-down version of the JIF standard in that it specifies certain constraints (such as not allowing all the different encoding modes), while in other ways, it is an extension of JIF due to the added metadata. The documentation for the original JFIF standard states:<ref>{{cite web
| url = http://www.w3.org/Graphics/JPEG/jfif3.pdf
| title = JFIF File Format as PDF
| access-date = 2006-06-19
| archive-date = 2021-01-13
| archive-url = https://web.archive.org/web/20210113062300/http://www.w3.org/Graphics/JPEG/jfif3.pdf
| url-status = live
}}</ref>

{{Blockquote|JPEG File Interchange Format is a minimal file format which enables JPEG bitstreams to be exchanged between a wide variety of platforms and applications. This minimal format does not include any of the advanced features found in the TIFF JPEG specification or any application specific file format. Nor should it, for the only purpose of this simplified format is to allow the exchange of JPEG compressed images.}}

Image files that employ JPEG compression are commonly called "JPEG files", and are stored in variants of the JIF image format. Most image capture devices (such as digital cameras) that output JPEG are actually creating files in the [[Exif]] format, the format that the camera industry has standardized on for metadata interchange. On the other hand, since the Exif standard does not allow color profiles, most image editing software stores JPEG in [[JFIF]] format, and includes the APP1 segment from the Exif file to include the metadata in an almost-compliant way; the JFIF standard is interpreted somewhat flexibly.<ref>{{cite web|url=http://www.faqs.org/faqs/jpeg-faq/part1/|title=JPEG image compression FAQ|author=Tom Lane|date=1999-03-29|access-date=2007-09-11|archive-date=2010-11-10|archive-url=https://web.archive.org/web/20101110054244/http://www.faqs.org/faqs/jpeg-faq/part1/|url-status=live}} (q. 14: "Why all the argument about file formats?")</ref>

Strictly speaking, the JFIF and Exif standards are incompatible, because each specifies that its marker segment (APP0 or APP1, respectively) appear first. In practice, most JPEG files contain a JFIF marker segment that precedes the Exif header. This allows older readers to correctly handle the older format JFIF segment, while newer readers also decode the following Exif segment, being less strict about requiring it to appear first.

===JPEG filename extensions===
The most common [[filename extension]]s for files employing JPEG compression are '''<code>.jpg</code>''' and '''<code>.jpeg</code>''', though <code>.jpe</code>, <code>.jfif</code> and <code>.jif</code> are also used.<ref>{{Cite web |title=Everything you need to know about JPEG files {{!}} Adobe |url=https://www.adobe.com/creativecloud/file-types/image/raster/jpeg-file.html |access-date=2023-08-18 |website=www.adobe.com |language=en-US}}</ref> It is also possible for JPEG data to be embedded in other file types&nbsp;– [[Tag Image File Format|TIFF]] encoded files often embed a JPEG image as a [[thumbnail]] of the main image; and [[MP3]] files can contain a JPEG of [[cover art]] in the [[ID3v2]] tag.

===Color profile===
Many JPEG files embed an [[ICC profile|ICC color profile]] ([[color space]]). Commonly used color profiles include [[sRGB color space|sRGB]] and [[Adobe RGB color space|Adobe RGB]]. Because these color spaces use a non-linear transformation, the [[dynamic range]] of an 8-bit JPEG file is about 11 [[f-number|stops]]; see [[gamma curve]].

If the image doesn't specify color profile information (''untagged''), the color space is assumed to be sRGB for the purposes of display on webpages.<ref name="auto">{{Cite web|url=https://www.w3.org/Graphics/Color/sRGB.html|title=A Standard Default Color Space for the Internet - sRGB|website=www.w3.org|access-date=2022-02-18|archive-date=2022-02-18|archive-url=https://web.archive.org/web/20220218083217/https://www.w3.org/Graphics/Color/sRGB.html|url-status=live}}</ref><ref name="auto1">{{Cite web|url=https://webstore.iec.ch/publication/6168|title=IEC 61966-2-1:1999/AMD1:2003 &#124; IEC Webstore|website=webstore.iec.ch|access-date=2022-02-18|archive-date=2022-02-18|archive-url=https://web.archive.org/web/20220218083451/https://webstore.iec.ch/publication/6168|url-status=live}}</ref>