In general, metadata is "data about data." In the case of XnView, metadata refers to information about images and image files.
Metadata is information about the image and/or file which cameras and image-generating programs attach to images to inform the user of a diverse number items such as: Date and time of composition, camera settings. It also can include commentary and embedded thumbnails.
It is displayed in Xnview's preview area in its own tab according to the kind of metadata used.
Users who consider this type of data superfluous or confusing can remove some or all it with XnView's Clean Metadata function.
The "Exchangeable image file format" (official abbreviation Exif, not EXIF) is a specification for the image file format used by digital cameras. The specification uses the existing JPEG, TIFF Rev. 6.0, and RIFF WAVE file formats, with the addition of specific metadata tags. It is not supported in JPEG 2000, PNG, or GIF.
Exif was created by the Japan Electronic Industries Development Association (JEIDA). Version 2.1 of the specification is dated June 12, 1998, and version 2.2 is dated April 2002 and is also known as Exif Print. The specification is not maintained by any industry or standards organisation, but it remains in almost universal use by camera manufacturers.
The Exif tag structure is taken from that of TIFF files. There is a large overlap between the tags defined in the TIFF, Exif, TIFF/EP and DCF standards. Tags defined in the Exif standard include:
- Date and time information. Digital cameras will record the current date and time and save this in the metadata.
- Camera settings. This includes static information such as the camera model and make, and information that varies with each image such as orientation, aperture, shutter speed, focal length, metering mode, and ISO speed information.
- A thumbnail for previewing the picture on the camera's LCD screen, in file managers, or in photo manipulation software.
- Descriptions and copyright information.
This information was taken from the Exif entry at Wikipedia entry, which see for more information.
IPTC metadata was developed by the International Press Telecommunications Council, which is a consortium of the world's major news agencies and news industry vendors. It develops and maintains technical standards for improved news exchange that are used by virtually every major news organization in the world.
In 1979, the IPTC defined a set of metadata attributes to be applied to images, and in 1994 Adobe defined a specification for actually embedding the metadata into digital image files. These are known as "IPTC headers." In 2001, Adobe introduced something called "Extensible Metadata Platform" (XMP), which is an XML schema for the same types of metadata as IPTC. The XMP specification describes techniques for how to embed the metadata in JPEG, TIFF, JPEG2000, GIF, PNG, HTML, PostScript, PDF, SVG, Adobe Illustrator, and DNG files.
This information was taken from IPTC entry at Wikipedia entry, which see for more information.