he extendable known as "JPEG Interchange Format" (JIF) is actually specified within Annex B of the standard. However, this "pure" extendable is hardly ever used, primarily because of the difficulty of programming encoders as well as decoders which fully put into action all facets of the standard and because of certain shortcomings of the standard:
Color room definition
Component sub-sampling enrollment
Pixel element ratio description.
Several extra standards possess evolved to address these issues. The first of these, released within 1992, was JPEG Document Interchange Format (or even JFIF), followed recently by Exchangeable image extendable (Exif) as well as ICC color profiles. Both of these formats use the actual JIF byte design, consisting of different guns, but in addition employ among the JIF standard's extension points, namely the application markers: JFIF use APP0, while Exif use APP1. Within these types of segments of the file, that were left for future use in the JIF standard and aren't read by it, these requirements add specific metadata.
Thus, in some ways JFIF is a cutdown version of the JIF standard for the reason that it specifies particular constraints (for example not allowing all of the different encoding modes), while in different ways it is definitely an extension of JIF due to the added metadata. The documentation for that original JFIF standard states: [12]
JPEG Document Interchange Format is a minimal extendable which enables JPEG bitstreams to be exchanged between a multitude of platforms as well as applications. This minimum format does not include any of the advanced features found in the TIFF JPEG standards or any application specific extendable. Nor should it, for the only purpose of this simplified format would be to allow the exchange of JPEG compressed images.
Image files that employ JPEG compression are generally called "JPEG files", and tend to be stored within variants of the JIF picture format. Most picture capture devices (for example digital cameras) which output JPEG are in fact creating files in the Exif structure, the format that the camera industry has standardised on for metadata interchange. On the other hand, since the Exif standard does not allow color profiles, most picture editing software stores JPEG within JFIF structure, and likewise incorporate the APP1 segment from the Exif file to include the metadata within an almost-compliant method; the JFIF standard is construed somewhat flexibly. [13]
Strictly talking, the JFIF as well as Exif requirements are incompatible because they each stipulate that their own marker segment (APP0 or even APP1, respectively) appears first. In exercise, most JPEG files have a JFIF gun segment which precedes the Exif header. This allows older visitors to correctly handle the older structure JFIF segment, while more recent readers additionally decode the following Exif segment, being less strict regarding requiring it to appear first.
