The only purpose of this historical perspective is to set the stage for the discussion.
TIFF stands for Tag Image File Format. TIFF 6.0 is owned by Adobe through acquisition of Aldus PageMaker (1986-1992). TIFF/EP "Electronic Photography" is owned by the ISO (2001). Participants include Adobe, Canon, Kodak, Nikon, Fujifilm, Olympus, and the CIE among many others. It has new metadata tags for sensor data and camera metrics. Apparently, not everything that Adobe and some other image editing software seem to need and want.
IPTC stands for International Press and Telecommunications Council (1965). The IPTC addresses author, copyright, and publishing related information.
EXIF stands for eXchangeable Image File Format. This format was part of the DCF standard created by JEIDA or the Japan Electronics Industry Development Association (1998), now JEITA. EXIF includes tags relating to the image data structure, camera make and model, copyright information, user comments and keywords, shooting data, timestamps, and such. The “Makernotes” tag is an area for manufacturers to store undefined and semi-private data. These tags may be imbedded in almost any image or media file type. DCF stands for Design rule for Camera File system. DCF also includes a CIFF standard, which stands for Camera Image File Format. This addresses rules for storage and management of removable memory media such as compact flash.
OECF stands for Opto-Electronic Conversion Function. It is the foundation of nearly all of the ISO/TC42 performance standards, documented in ISO 14524. It defines the relationship between exposure, or reflectance, and digital count values of a capture device. It is most often used or referenced in other performance standards, test image targets, and benchmarks.
XML, eXtensible Markup Language is an industry standard from the W3C, or The World Wide Web Consortium (1996-2001). It is in turn based on an ISO SGML standard. This is primarily a syntax definition. It is a framework for encapsulation of common tags and semantics for multiple industries.
XMP, eXtensible Metadata Platform is owned by Adobe (January 2004). It is an Adobe implementation of XML for image and camera related data tags.
These are all employed to some extent in the raw image formats that are popular today. In addition, Adobe has proposed its DNG (Digital NeGative) format as a standard for all raw files.
Metadata is defined as data that describes data. Like a dictionary it consists of two basic types of information. The first is the syntax, like the spelling and pronunciation of a particular word. For computer data, this helps us extract or “parse” the words. The second part is the semantics, like the dictionary usage and meaning of a particular word. This is described in the reference standards or through accompanying documentation. By definition, proprietary data would not be fully described in a standards document.
Image metadata is simply information about the image. This is recorded by the camera to describe the raw data and information about the camera, including camera settings. Metadata written by a digital camera may include physical properties of the camera, exposure information, color information, white balance, camera settings, date and time, GPS, lens information and more. Since most of this is not adequately covered by existing standards, much of it is included in the EXIF “Makernotes” area.
The metadata written by a digital camera in a RAW file is needed to accurately render the raw data into a finished image. Some portions of this metadata are critical to proper image processing. Other metadata items can provide important clues to help describe and categorize the image or to analyze your shooting skills.
Cheers, Rags :-)
So long, and thanks for all the fish!
Rags Int., Inc.
204 Trailwood Drive
Euless, TX 76039
May 21, 2005
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