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One of the many advantage of using a digital camera is that it probably records all sorts of information about each image. Most cameras records details of the exposure, ISO rating and equipment in use without the photographer even being aware of what is happening. This information is collectively known as metadata, and can be extremely useful.

Metadata is useful not only because it records when and how pictured were taken but also because it can be used to review the images that did or did not turn out as expected. Images that were failures because of lack of depth of field, for example, can be reviewed against the relevant metadata to see what caused the problem and how similar failures might be avoided in the future.

Metadata may divided into a number of categories. These are:

  • descriptive metadata - this describes the actual visual content of an image;
  • administrative metadata - this records data that cannot be obtained or inferred by visual inspection of an image;
  • rights metadata- this establishes ownership of an image and the conditions under which it may be used; and
  • technical metadata - this included data relating to the physical properties of the contents of an image.

Metadata is presented in established groups, each of which contains a number of standard fields. Exchangeable Information File Format (EXIF) data provides details in a standardized format of camera type, shutter speed, aperture, time, date, the lens and its focal length, ISO setting, white balance, flash and so on. International Press Telecommunications Council (IPTC) data records other information relevant to each image such as the author's name, image description, keywords, copyright information etc. It is consequently more useful to image libraries and the press. The data can be customized and may serve to increase the security of a photographer's images. Editing software such as Photoshop can be used to set of change the data. Extensible Metadata Platform (XMP) data was introduced by Adobe in 2001 in an attempt to standardize the definition, creation and processing of metadata in various types of file. XMP files (with an .xmp file extension) are created by Adobe Bridge when it is unable to add certain information into a file headed, such as adjustments made to RAW conversion settings for an image.

Metadata is generally invaluable for cataloguing and archiving because some fields are very useful for searching. For instance, a photographer might wish to select all the images taken at a particular time of day, or all those taken at shutter speeds slower than 1/30 second.


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