JPEG File Interchange Format

Template: Infobox file format / Maintenance / MagischeZahlHex missing FF D8

The JPEG File Interchange Format (JFIF ) is a 1991 developed by Eric Hamilton graphic format for storing images that have been compressed by the JPEG standard. The file name extension is mostly jpg, rare jpeg, jpe or jfif used. JFIF is the World Wide Web the most widely used image format for photos.

The JPEG standard specifies only the compression process, but not how the resulting image data must be stored so they can be exchanged between different computer programs. For example, JPEG does not specify which color space to use. JFIF is a method to store JPEG data; other possibilities include the published by the Joint Photographic Experts Group Still Picture Interchange File Format ( Spiff ) and JPEG Network Graphics. Commonly referred to " JPEG file " a JFIF file.

JFIF makes only a small part of the possibilities offered by JPEG use: so is approved as a color model only YCbCr and not RGB; for entropy coding only Huffman coding is allowed. Additions are some mechanisms for synchronization and resynchronization in case of transmission error.

File Format

The size of JPEG images is limited at 65,535 × 65,535 pixels in JFIF.

JFIF image files consist of a header (which may be empty) and the actual data to be initiated by a SOI marker FF D8. On these markers of JFIF tag follows: FF E0 00 10 4A 46 49 46 00 01 4A 46 49 46 The sequence is the ASCII representation of " JFIF ". Common image programs can also process files without JFIF day.

The JFIF files into segments ( in TIFF designated as day ) divided. The segments are generally constructed in the following form: FF xx s1 s2 starts the day. FF is a hexadecimal value and corresponds to the decimal 255 The xx determines the type of the tag. 256 * S1 S2 is the length of the segment. The segments more pictures can hide, often a small thumbnail for quick preview. Individual segments can occur more than once.

An example of a Copyright Day: EE FF 00 26 'File written by ...'

An example of a comment tag: FF FE s1 s2 ' This photo shot is dated ...'

Building a JFIF file:

The lengths of the segments incidentally also include the space for the length data itself: an empty segment therefore has length 2, as this s1 and s2 corresponding to the length of the components themselves.

At the start-of- scan (SOS ) segment (marker FF DA) directly follow the compressed data to the start of the next segment, which is indicated by the next marker. If the data within a FF occur, this will be marked with a following 00 (zero). Other values ​​indicate the occurrence of a new segment or marker. Exception: Follow the FF of the restart marker (D0 - D7) then the data set directly behind continued: FF FF D0 DA ... data ... data ... ...

As a decoder only interested in data between a start marker and end marker a, Exif, IPTC -NAA standard information and even entire XML or other files, it is also possible to accommodate after DataContainer procedures in the JFIF file. However, the extensions are not JFIF compliant. It is recommended to remove these files before publishing an image when it contains private information.

Exif metadata

  • Incompatibility of previous versions of Exif

Add image files in JPEG format and metadata in Exif format can be saved; many digital cameras store information here about manufacturers and software version from. License data can also be stored. Attention was the habit of some image editing programs to store thumbnails in Exif field that are not necessarily matched with a change of the image file; not intended for publication, parts of the image file so you can get to the public in low resolution anyway.