Feb 3, 2005

A primer on EXIF Information

EXIF stands for Exchangeable Image File Format. Exif is a variation of JPEG, used by almost all digital cameras to record extra interchange information to image files as they are taken. Here is an EXIF primer for you from Jeff Schewe and Seth Resnick of Pixel Genius.

By simple definition, "Metadata" is data about data. Metadata is structured information that explains, describes, locates or otherwise makes using the original primary data more efficient or useful. A wide variety of industries are using metadata, but for the purposes of digital imaging, there are currently only a few technical structures or "schema" that are being employed. A schema is a set of properties and their defined meanings such as the type of value; date, size, URL or any useful designation.

FILE INFOAt this point in time, the primary image metadata schema has been "File Info" which is non-image data embedded within Photoshop image files. Originally employed by the newspaper industry, IPTC (International Press and Telecommunications Council) metadata contains only a few fields of limited text used to help organize and distribute photographic images for newspaper publishing. "File Info" which is the Photoshop implementation of the IPTC specification plus additional data fields, defines both the storage format as well as the actual metadata. Text fields in the current specification include but are not limited to; Caption, Caption Writer, Headline, Special Instructions, Keywords, Category, Supplemental Categories, Urgency, Byline, Byline Title, Credit, Source, Object Name, Date Created, City, Province-State, Country Name, Original Transmission Reference, Preserve Additional Information. Mark as Copyrighted, and URL are additional fields beyond the IPTC specification.

The File Info fields allow only a scant amount of text information to be embedded within the file, but it is critical that this information moves through the newspaper publishing system locked together with the file. The thousands of digital images used in major newspaper companies would quickly become useless if the images lost this important embedded information. Surprisingly, a large number of Photoshop users don't even realize these metadata fields already exist. Photographers routinely send out digital images without even marking them as Copyrighted or embedding simple contact information.

EXIFSeveral years ago, a group of major photographic manufacturers, the Japan Electronic and Information Industries Association (JEITA) developed a new metadata schema called EXIF (Exchangeable Image File Format). This schema is designed to embed in a digital capture-right at the moment of exposure-certain information relating to the camera's function, image parameters and miscellaneous additional information. While mildly useful for photographers, EXIF metadata seems to be designed primarily for the camera manufacturing industry. While the EXIF metadata schema has been specified since September of 2000, only Photoshop 6.0 can preserve the EXIF data basically intact. Previous Photoshop versions as well as most other image editing applications will strip the metadata from the file if the image is opened and re-saved. To add to the frustration of photographers who may wish to use this data, the camera manufacturers have failed to supply a Photoshop compatible plug-in that could read or use the EXIF metadata information. Most users need to rely on the camera manufacturer's software to even see the data and few offer the ability to save or export the information.

To be honest, this lack of functionality of the camera software is what led Pixel Genius to create the freeware MetaReader plug-in. The MetaReader plug-in can allow users to read and export the embedded metadata to text files for importing into database applications. Coupled with the File Info and EXIF metadata, Photoshop 6.0's own metadata includes the file name, color mode, bit depth and image size. This combination of metadata and MetaReader will allow photographers to finally use the metadata for organizational and other useful purposes.

Unfortunately, looking at all the various schema currently used in image file metadata, it's also clear that the explicit needs and desires of imaging artists and photographers have not been met. The groups that designed and specified the schema had their own agendas, which up until this point, seem to have excluded photographers. To have EXIF or any additional schema reach broad adoption and acceptance, the creators of digital images need to be brought into the process of designing and specifying what metadata can be used for.

At Seybold San Francisco in the fall of 2001, Adobe announced a new technology initiative called XMP (Extensible Metadata Platform) that will establish a common metadata framework that standardizes the creation, processing and interchange of document metadata across publishing workflows. Adobe has also committed to the W3C (World Wide Web Consortium) standards including XML (Extensible Markup Language). Thus, XMP will be XML compatible. What does this mean for the future of metadata and it's usefulness to photographers and imaging artists? XMP holds the promise of providing a significant and extensive platform for a wide array of various metadata implementations. In the near future, both public and private metadata schema will enjoy a widely adopted "framework schema" that will enable a rich and extensive capability to use metadata for critical technologies such as Digital Rights Management (DRM) and Digital Asset Management (DAM).


We are sure metadata sounds interesting to a lot of people, but perhaps it's difficult to visualize what it can do. The world of metadata is here now, but because of the lack of coordination between manufacturers and organizing bodies, much of the potential remains unrecognized. We want to show some examples of metadata and how it can help photographers, both now and in the future.

The following metadata is the currently available sum of the various metadata in a digital capture by Canon's new EOS-1D camera and Photoshop combined. Numerous fields are of little use to most photographers. However, by exporting this data to a database application and formatting the layout, the fields of special interest to photographers can be made available. This re-purposing of the metadata is important to the usability of the data.

Photoshop Metadata:

Mode: RGB Color, 8 bits
Size: 288 x 192 (4 x 2.66667 inches)

Photoshop File Info:
Caption: Close-up of a Eupholus Quinitaenia from New Guinea. This beetle is approx 1 inch in size.
Caption Writer: seth resnick
Headline: none
Special Instructions: none
Keywords: beetle, insect, environment, antenna, New Guinea
Category: none
Supplemental Categories:
Byline: seth resnick copyright 2001
Byline Title: author/photographer
Credit: none
Source: seth resnick
Object Name: none
Date Created: 20011012
City: Boston
Province-State: Massachusetts
Country Name: USA
Original Transmission Reference: none

Canon EXIF Metadata:
File Name: 50CA0994.TIF
Camera Model Name: Canon EOS-1D
Shooting Date/Time: 10/12/01 17:42:34
Shooting Mode: Manual
Tv(Shutter Speed): 1/80
Av(Aperture Value): 5.6
Metering Mode: Evaluative
Exposure Compensation: 0
ISO Speed:100
Lens: 65.0mm
Focal Length: 65.0mm
Image Size: 2464x1648
Image Quality: RAW
Flash: On
Flash Type: External E-TTL
Flash Exposure Compensation: -1/3
Shutter curtain sync: -curtain sync
White Balance: Color Temperature (5000K)
AF Mode: Manual Focus
Tone Curve: Standard
Sharpness level: 0
Pattern sharpness: Standard

File Size: 3573KB
Serial Number: 100-0994
Custom Function Settings
00:Focusing Screen
01:Finder display during exposure
0:No viewfinder display
02:Shutter release without CF card
0:Possible without CF card
03:ISO speed expansion
1:Expanded sensitivity
04:Shutter button/AE lock button
0:AF/AE lock
05:Manual Tv/Av set. for M exp.
0:Tv value: Main dial, Av value: Quick Control dial
06:Exposure level increments
0:1/3-stop set, 1/3-stop comp.
07:USM lens electronic MF
0:Turns on after One-Shot AF
08:Top LCD panel/Back LCD panel
1:ISO/Remain. Shots
09:Auto bracketing sequence/cancel
0:0,-,+/Auto cancellation
10:AF point illumination
2:On without dimming
11:AF point selection method
0:AF point selection button + Main (horizontal) / Quick Control (vertical) dial operation
12:Mirror lockup
13:Number AF points/Spot metering
1:11/Active AF point
14:Auto reduction of fill flash
15:Shutter curtain synchronization
0:1st-curtain synchronization
16:Safety shift in Av or Tv
17:AF point activation area
1:Expand(TTL. of 7 AF points)
18:Switch to registered AF point
0:Assist button + AF point selection button
19:Lens AF stop button function
0:AF stop
20:AI SERVO tracking sensitivity
Drive Mode: Single-frame shooting
Owner's Name: seth resnick copyright 2001
Camera Body No.: 00129

Some of the above data is known as "public data" and some of it is referred to as "private data". Currently, only public EXIF data is readable by MetaReader. However, the key concept is that information such as shown above is currently available from camera manufacturers. Unfortunately, much of the software being used today strips out, or at the very least, does not reveal any of this data. Some of the data has phenomenal potential for the imaging business. For example, suppose two photographers are on assignment and shoot from the identical position with identical lighting. For all practical purposes the images would be identical and one would be unable to differentiate who shot which image. By using metadata you would be able to see the serial number of the camera body and the owners copyright, providing conclusive proof of ownership.

The ability to keyword using extensive metadata currently exists. Using this ability to embed keywords would mean that placing an image into a stock library could eliminate or reduce an incredible amount of time currently spent on key-wording images. It is estimated that the current cost of placing a film based image into a stock library and duplicating it can run as high as $140.00 per image. If the key-wording time spent by an agency was reduced, along with solving other image identification problems, the actual cost of placement within a system could be drastically reduced.

Photographers and imaging artists will soon be able to take advantage of metadata for many aspects of their imaging business. Licensing information for an image along with the means of password security for opening the file could be incorporated into a metadata schema. Imagine being able to embed a unique image identification "ID" that will travel wherever the image goes. Even invoices and transactions could be completed using metadata. Users could also employ metadata for tracking billable time while image processing. A user could also track exactly what was done to an image file, and when.

The key to being able to develop beneficial uses for metadata lies in the "end users" providing substantial input to the development of new metadata schema. That's one of the main reasons that the members of Pixel Genius want to expose the benefits of using metadata to a wider audience of potential users. We at Pixel Genius see a horizon of opportunity to help photographers, illustrators and stock agencies develop and deploy the benefits of metadata in a wide array of applications. In the near future, we plan on offering a developing line of robust applications that will use metadata to help the imaging industry become far more efficient and profitable.

Pixel Genius is a collaboration of industry leading experts dedicated to producing leading edge products for the photographic and digital imaging industries. In addition to creating products, the team is available for 3rd party product design and development. Please contact us for additional information. MetaReader, our first product, is freeware for individual use and currently available for download from our web site (registration required).