Background: Image Metadata
- about EXIF, IPTC, etc.
Metadata is supplementary information about images. This includes technical
descriptions of exposure conditions, date, location, author, content description, workflow
data, and keywords for archiving and retrieving. The importance of metadata increases with the
amount of images which are to be handled.
There are (at least) 3 completely different approaches for storing image metadata:
- Using a Database. This is what Picasa (and others) do. The problem with
this approach is that only the database program is aware of the context between metadata
and images. Thus, metadata can get lost when files are copied or transfered.
- Using ADS ("Alternate Data Streams"): This is a feature of the Windows NTFS
file system. ADS data is stored in hidden files which are attached to the visible image
file - as long as this file stays on the NTFS file system. ADS data will get lost when, for
example, you copy the file to a CD-ROM or a memory stick or when you transfer it over the
Internet. You typically access ADS data by the Windows Explorer "File Properties/File Info"
- Using IPTC and EXIF: Metadata conforming to one of these open
standards can be stored within the image file itself. If such a file is copied or moved to
another location, the metadata stays with the image; there are no redundancy problems which
typically arise with database or ADS storage.
These 3 approaches are not compatible with each other.
Panorado 4.0 follows the
IPTC/EXIF approach, as this is the most convenient way to handle image data which is likely to
be copied or transfered.
JPEG files (which is by far the most popular file format for photographs) are by
design able to include EXIF and IPTC data along with
the image data.
What is EXIF?
Digital cameras usually create JPEG image files which also contain EXIF meta
information. EXIF (Exchangeable image file format for Digital Still Cameras) is a standard
introduced by the Japan Electronic Industry Development Association (JEIDA).
Most of these data concerns exposure conditions:
- Camera manufacturer and camera model
- Date & time of exposure
- Image orientation (landscape/portrait)
- Use of flashlight
- Focal length
- Exposure time
- Exposure bias
- Light source
- Metering mode
- Exposure program used
- ISO eqivalent
There are also specifications for other data which is used less frequently, for
example, for different kinds of text information:
- Image description
Some other tags are for the inclusion of GPS data like
- Current position
- Direction of image
- Speed and direction of movement
In addition, most camera manufacturers write device-specific data in a proprietary
format. I seems that some of these formats can be misinterpreted if the data is moved within
the file - which is absolutely allowed by the EXIF specification.
In a technical sense, EXIF data in a JPEG file is completely independent from IPTC data - though some textual information of the two standards overlap.
What is IPTC?
IPTC stands for the possibility to attach metadata to image files for archiving
and data interchange purposes.
This metadata is composed of texts concerning the photographer, the image content, the
location where the photograph was taken, and the imaging workflow.
In 1991, the IPTC (International Press Telecommunications Council) and the NAA
(Newspaper Association of America) approved the so-called Information Interchange Model - IIM.
Adobe Systems Inc.'s Photoshop software then used this standard (which became
generally known as IPTC Header) for attaching descriptions to JPEG and TIFF images.
In the meantime, IIM evolved into a de-facto standard for image archives, though there were
some competing standards (e.g. EXIF, Dublin Core).
In 2004, a new standard was published, based on XML schemas: XMP (Extensible
Metadata Platform). As the name suggests, it is extensible. But - like IIM - it has a hard
core: The IPTC Core standard (which was defined as a joint effort of IPTC, Adobe and
IDEAlliance) inherited 16 of the 19 IIM datasets and added 14 new ones.
User interface guidelines suggest to present the IPTC Core fields in 4 groups:
Contact, Content, Image, and Status.
A sophisticated synchronization mechanism is recommended for achieving compatibility with
the "legacy" IIM standard.
In a technical sense, IPTC data in a JPEG file is completely independent from EXIF data - though some textual information of the two standards overlap.
Manage images - with or without a database?
As described above, image metadata can be inserted directly into image files. Some
image archiving programs, instead (or in addition), store metadata in a central database. This
can help to accelearate the retrieval of images which are scatterd across storage media, as
image files don't have to be read directly.
Such a program normally starts with a complete scan of all available storage media,
which can take some time. When this is done, you can retrieve, sort, and annotate images quite
fast. One example for this approach is Google's Picasa browser.
This is nice - as long as any changes to the images is exclusively controlled by the
archiving program. But you should expect to get trouble as soon as images will be edited,
moved, deleted, exported, or imported, without the database "knowing". There will be
reduncancy, which means that there is contradictory information about an image, and this can
be really confusing.
Panorado 4.0 takes a
different approach - a safe approach, without a database:
- All metadata stay with the images they belong to.
- There's no redundant metadata.
- You don't have to care about storage formats.
- You can use any method you like to handle files, including drag-and-drop to or
- Right-click on an image to start your favorite graphics editor.
- Any changed images will be redisplayed automatically.
- There's a powerful Image Finder tool for retrieving images by various categories,
and for batch-processing.
What is metadata good for?
There are a lot of possibilities to make use of metadata - but in reality, it's still
Panorado 4.0 uses metadata
- for an editable overview of image properties,
- for displaying subtitles in presentations (slide shows),
- for image retrieval by keywords,
- for fast rendering of preview images (thumbnails),
- for rotating images in steps of 90 degrees,
- for describing exactly the field of view of (partial) panoramas,
- for search by location and Google Earth access using GPS coordinates.