Sustainability of Digital Formats: Planning for Library of Congress Collections

The Exchangeable Image File Format (Exif) family is based on a specification that combines established file encoding standards such as JPEG, TIFF, and WAV with structured, embedded metadata referred to as Exif data. These specifications primarily focus on recording technical information. The first version of the JEIDA (Japan Electronic Industry Development Association) authored specification published in 1996 is titled Exchangeable image file format for Digital Still Cameras: Exif and was primarily associated with digital photography (with the goal to document "the method of recording image data in files"). However, starting with version 2.1, this was expanded to sound recordings to capture "the method of writing audio data in files." In essence, they define the formats of images, sounds, tags, and other metadata found within files generated by digital still cameras and similar systems.

The Exif specification is divided into two main categories: image file specifications and audio file specifications. The image file specifications support TIFF- and JFIF/JPEG-based encoded files, while the audio file specifications are geared toward WAVE files. While the Exif specification defines criteria for TIFF, JPEG, and WAV files, Exif data may also appear in other formats that don't adhere strictly to the specification.

The official title of this standard is "Exchangeable image file format for digital still camera" ,however, the standard caters to both still image and audio files, encompassing the Exif image and the Exif audio file specification. It's worth noting that this standard is applicable to various devices, including digital cameras, digital video cameras (DVC), smartphones, digital photo frames, PCs, and printers, all of which have functionalities related to capturing, generating, recording, displaying, editing, and printing images.

Exif metadata tags include descriptive metadata, copyright details, camera settings, technical image data, date and time information, geographic data, and thumbnail storage.

Specifically for image data, the metadata fields include number of pixels, pixel aspect ratio (required to be square 1:1), pixel composition and sampling (describing color space with the required values of RGB 4:4:4 and either Y:Cb:Cr = 4:2:2 or Y:Cb:Cr = 4:2:0), and image data arrangement.

For audio data, metadata fields include sampling frequency (with defined values per compression scheme), bit size, channels (monaural or stereo [2 ch])) and compression scheme (with options of uncompressed Pulse Code Modulation [PCM], uncompressed µ-Law or Mu-Law or compressed Adaptive Differential PCM Sound Format [ADPCM]) within a WAVE Audio File Format container.

When these formats are used as Exif/DCF (Design rule for Camera File System) files in conjunction with the DCF Standard (which guarantees interoperability among various device types), their scope extends to devices, systems, recording media, and application software designed to handle them (as specified in Version 3.0 of the specification).

See History for a timeline of the Exif specification versions and Self Documentation for version-declaring embedded metadata.

The Exif version is stored as 4 bytes at the start of the file classified as A1, A2, B1, and B2. A1 and A2 hold the upper part of the version and B1 and B2 store the lower. When updating the standard version, the following rules apply:

1. If changes allow data readers to recognize conventional information and skip data with new functions, the lower part of the version (B1, B2) changes.

2. If there's a risk that an older data reader might malfunction due to new specs, the upper part of the version (A1, A2) changes.

Players should support playback of files from earlier versions of the standard. See section 4.6.6.1.1 of the specification for more details.

See TIFF Uncompressed File with Exif Metadata and JPEG Encoded File with Exif Metadata. Exif tags are included in Tags for TIFF and Related Specifications.

See TIFF Uncompressed File with Exif Metadata and JPEG Encoded File with Exif Metadata.

Version 2.0 introduced sRGB support.

Versions 2.2 and forward have tags which permit the identification of files that use sRGB.1. Exif 2.2 also allows the identification of the Adobe RGB color profile. There appears to be no Exif tag for the ICC profile for a capture device. See Exif Exchangeable Image File Format, Version 2.2 for more detail.

Stereo or monoaural only.

See specifications for Version 2.2 and Version 3.0 for more details.

Global positioning system (GPS) support was introduced in Version 2.0. Further improvements to GPS support were added in Version 2.2.

Supporting tags for composite images were added in Version 2.32.

Version 3.0 added support for UTF-8/Unicode, Box-structured data, and added or changed the definitions for several tags including: Title, Photographer, ImageEditor, CameraFirmware, RAWDevelopingSoftware, ImageEditingSoftware, MetadataEditingSoftware, Software, Artist, ImageUniqueID, GPSAltitudeRef, GPSMeasureMode, XResolution, YResolution, ResolutionUnit, and FlashpixVersion. UTF-8 character support became Exif compliant in this version.

When Exif is utilized with JPEG files, it stores Exif data within one of JPEG's predefined utility Application Segments known as APP1 (with the segment marker 0xFFE1). Essentially, this segment functions as a container for an entire TIFF file. In the case of Exif usage with TIFF files, including those embedded within other TIFF files, the TIFF Private Tag 0x8769 establishes a sub-Image File Directory (IFD) that houses Exif-specific TIFF Tags. Furthermore, Exif defines a Global Positioning System sub-IFD through the TIFF Private Tag 0x8825 to store location data, and it specifies an "Interoperability IFD" within the Exif sub-IFD using the Exif tag 0xA005.

EXIF was developed by Japan Electronic Industries Development Association (JEIDA). In 2000, JEIDA and the Electronic Industries Development Association (EIAJ) merged to form the Japan Electronics and Information Technology Industries Association (JEITA). In 2009 the Camera and Imaging Products Association (CIPA) joined JEITA in the management of the Exif standard. CIPA was established in 2002 as a successor to the Japan Camera Industry Association (JCIA). CIPA consists of companies engaged in the development, production, or distribution of digital cameras, imaging-related products, and software.

About JEITA: "The Japan Electronics and Information Technology Industries Association (JEITA) was formed on November 1, 2000, through the merger of the Electronic Industries Association of Japan (EIAJ) and Japan Electronic Industries Development Association (JEIDA). JEITA is a new industry organization in Japan with activities covering both the electronics and information technology (IT) fields." (http://www.jeita.or.jp/english/about/what/).

About CIPA: The Camera and Imaging Products Association (CIPA) was established in 2002 as a successor organization to the Japan Camera Industry Association (JCIA). JCIA participated in the original development of Exif. CIPA "is an industry association consisting of companies engaged in the development, production, or distribution of digital cameras, imaging-related products, and software" (http://www.cipa.jp/guide/documents/e/en0203.pdf).

Timeline for Exif development:

• Version 1.0. Published October 1995.
• Version 1.1. Published May 1997
• Version 2.0. Published November 1997.
• Version 2.1. Published December 1998.
• Version 2.2.
• Version 2.21. Published September 2003 as a set of changes. Promoted as "Exif Print."
• Unified Version 2.21. Published September 2009.
• Version 2.3. Published April 2010.
• Version 2.3 (Revised 2012). Published December 2012 (with two explanations corrected).
• Version 2.31: Published in July 2016.
• Version 2.32: Published in May 2019.
• Version 3.0: Published in May 2023.