Exchangeable Image File Format
The Exchangeable Image File Format (official abbreviation Exif ) is a standard format of the Japan Electronic and Information Technology Industries Association ( JEITA ) for the storage of metadata in digital images. The last version of the standard (2.32, April 2010, last revision in May 2019) was formulated by a cooperation between JEITA and the Japanese organization CIPA ( Camera & Imaging Products Association , successor organization to JCIA - Japan Camera Industry Association).
Technical information on the recording, including camera model, time of recording and camera settings, is stored in the Exif data of an image file.
Other metadata standards are the IPTC-IIM standard and the Extensible Metadata Platform (XMP).
Areas of application
Exif data is written directly into the file of images in JFIF (JPEG) or TIFF formats - in the so-called header (area at the beginning of the image file, before the actual image information). In the meantime, practically every digital camera stores this additional information about the recording in the picture, and the camera applications of most smartphones also create pictures with Exif data.
Numerous image processing programs and other software can output this data. In addition, Exif data can be used for audio files.
Exif entries
Almost all modern digital cameras can use the Exif standard and save numerous recording parameters with each shot, such as:
- Date and time
- Orientation (image rotation by 90, 180 or 270 °)
- Focal length
- Exposure time
- F-number
- Exposure program
- Exposure index ( ISO value )
- Geographic coordinates (this data can be added by geotagging ) and elevation above sea level
- Preview image ("Thumbnail")
- Camera type
Further useful information can be added later in the form of so-called IPTC data (International Press Telecommunications Council). In addition to Exif, the IPTC standard is another standard that is mainly used in photojournalism . Examples of typical IPTC fields are:
Examples of exif tags
There is various information in the Exif data, they are stored in the form of so-called "tags" (English "tag" = identification, marking). The tags each consist of a pair of a name and a value. The values can be of different types and lengths. For clear identification, each tag has a number (tag ID) consisting of 16 bits, which can be represented as a decimal number or four hexadecimal digits (with the suffix “.H” according to the standard or often with the prefix “0x”). The national language representation of the names and the formatting of the (numerical) values is done by display programs. The tags are standardized and provide information about the camera settings under which the picture was taken, such as the following:
ID (hex.) | Surname | meaning |
---|---|---|
9000 | ExifVersion | Version of the Exif standard |
010F | Make | Name of the camera manufacturer |
0110 | Model | Name of the camera model |
0112 | Orientation | Image orientation portrait / landscape |
9003 | DateTimeOriginal | Recording date |
829D | FNumber | F-number |
829A | ExposureTime | Exposure time |
8833 | ISOSpeed | Image sensor sensitivity |
9207 | MeteringMode | Exposure metering method average / spot / multi-segment |
013B | artist | Creator / photographer |
8298 | copyright | Copyright information |
9286 | UserComment | General comment or image description. Unicode capable |
010e | ImageDescription | Title of the picture and brief description of the picture |
In addition to the standard fields, manufacturers can also insert specific "maker notes" that contain manufacturer-defined, proprietary information that is either not defined by the Exif standard or whose content is not disclosed for other reasons. Examples:
- Focus mode
- AF point
- Focus Distance
- Total Pictures
Example of Exif data of a picture taken with a Sony Alpha 380
Name of the saved file | DSC04923.ARW |
Camera model | Sony Alpha 380 |
Firmware | Firmware version 1.1 |
Recording date / time | November 27, 2011 3:39:28 PM |
Author / photographer | John Doe |
Copyright notice | Copyright: Max Mustermann |
Name of the owner | John Doe |
Recording mode | A (aperture priority) |
Tv ( shutter speed ) | 1/6 |
Av ( f-number ) | 2.8 |
Measurement mode | Multi-field measurement |
Exposure compensation | 0 |
Film speed (ISO) | 100 |
Automatic film speed (ISO) | Out |
lens | Sony AF 20mm F2.8 |
Focal length | 20.0 mm |
Image size | 4600 × 3064 |
picture quality | Fine |
lightning | Out |
FE flash exposure lock | Out |
White balance | Automatically |
AF mode | Manual focus |
Color space | sRGB |
Color depth | 36 bits |
Noise Reduction for Long Exposure | 0: Off |
Automatic exposure optimization | 0: standard |
Edge light correction | Activate |
File size | 18842 KB |
Dust extinguishing data | No |
mode of transport | Single shot |
Live image recording | Out |
The data from the objective can be used by panorama programs to correct certain imaging errors before assembly. This camera and the associated software also use the data for peripheral light correction in order to eliminate slight vignetting caused by brightening.
Possible problems
privacy
With the metadata automatically saved by the camera, details such as date, time, location, preview image etc. may inadvertently be passed on or published. Depending on your point of view, this can be desirable or undesirable. So was z. For example, the whereabouts of the then volatile John McAfee is known through the careless publication of a photo with GPS coordinates taken during an interview with a journalist.
At least the company Google uses the EXIF data, the file name and alternative image texts in order to better understand the images.
Matt Cutt, a former employee at Google, said in 2014 that EXIF data from images could possibly be a ranking factor for Google Image:
- "It's something that Google can analyze and I think we reserve the right to use it in the ranking!"
Conversely, there is a controversy as to whether search engine optimization (SEO) can be carried out using the image information.
With the help of suitable computer programs, all Exif data can be removed from image files.
The company Facebook Inc. automatically removes metadata from on Facebook uploaded images. The company was banned from doing this in Germany in 2016. The judgment was justified with the deleted evidence of the author. Image metadata may not be removed or changed without authorization in accordance with Section 95c of the Copyright Act . Image files from which it is known that metadata has been removed without authorization may not be redistributed without authorization.
compatibility
When editing photos with common image editing programs, some Exif data can be changed in such a way that they are no longer displayed with common image viewers. The problem arises from the fact that, according to the JFIF specification, the JFIF-APP0 marker must be located directly behind the SOI marker, while according to the Exif specification, the Exif-APP1 marker must be located there. Strictly speaking, inserting Exif data into a JFIF file creates a different file format that is not JFIF compliant. However, newer JFIF libraries (e.g. from the Independent JPEG Group (IJG) from 2001) recognize existing Exif data and then leave the Exif APP1 marker unchanged.
Time zones
Right from the start, the Exif specifications did not define any time zones. There is no standard time zone such as B. UTC specified. Therefore problems with the date and time can occur when exchanging images across different time zones or when switching between summer and winter time. It was not until Exif version 2.31 (July 2016) that time zone tags were introduced: “OffsetTime”, “OffsetTimeOriginal” and “OffsetTimeDigitized”.
Embedding malicious code
Using the Exif metadata area, it is possible to smuggle in and execute program code on external web servers. To do this, an image is uploaded to the server using a file upload form. However, this has the extension of an executable file (for example .aspx or .php). However, based on the actual content, the server assumes a harmless picture. The actual malicious code is located as metadata in the Exif area. If the manipulated file is then retrieved from the server via a URL , it is executed based on the file extension instead of being displayed. In the next step, the database or the domain controller can be taken over. If the server checks when the file is uploaded whether the file extension matches the actual content, such an attack is impossible.
Versions
- 2.1 of June 1, 1998
- 2.2 (project name "Exif Print") of February 20, 2002 (published between February and April 2002)
- 2.21 (with Adobe RGB support) from July 11, 2003 (published in September 2003 immediately after DCF 2.0)
- 2.3 of April 26, 2010, revision May 2013
- 2.31 of April 26, 2010, revision April 2016
Web links
- CIPA / JEITA : Exif specification 2.32. (PDF) In: CIPA website. Retrieved May 1, 2019, December 17, 2019 (English translation of the relevant original Japanese document).
- digicam-experts What are EXif data
Software and tools
- Phil Harvey's ExifTool , a popular Perl library for viewing and editing Exif entries. Since Perl is available for many platforms, the same applies to the ExifTool. Executable command line versions are available for Windows and Mac OS X that run without Perl installed. Other examples of the use of this library are
- ExifToolGUI for Windows , a graphical user interface for Windows, English
- Jeffrey's Image Metadata Viewer , read out Exif data online, English
- GeoSetter , a tool for geotagging , German and English
Individual evidence
- ↑ CIPA / JEITA : Exif specification 2.32. (PDF) In: CIPA website. Retrieved May 1, 2019, December 17, 2019 (English translation of the relevant original Japanese document).
- ↑ sno.phy.queensu.ca: EXIF tags
- ↑ Achim Sawall: John McAfee located with iPhone geolocation. Golem.de, December 4, 2012, accessed October 5, 2013 .
- ↑ a b https://imageseo.io/does-exif-iptc-impact-images-seo/ Does EXIF data impact image SEO?, Online article by ImageSEO, accessed on May 7, 2020
- ↑ Hamburg Regional Court, file number 308 O 48/15
- ↑ https://www.ds-law.eu/lg-hamburg-iptc-daten-facebook/ LG Hamburg confirms protection of IPTC data on Facebook , message on D. Seiler's private website of November 20, 2016, accessed on May 7, 2020
- ↑ https://dejure.org/gesetze/UrhG/95c.html Copyright Act Part 4, Section 95c: Protection of the information required for rights management , Section 3
- ↑ Guido full conditions: Exif Patch Document. January 7, 2001, accessed June 10, 2015 .
- ↑ CIPA / JEITA : Exif specification 2.31. (PDF) In: CIPA website. July 14, 2016, Retrieved May 25, 2017 (English translation of the relevant original Japanese document).