Photographic EXIF Data

July 12, 2008

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July 12, 2008

I’ve mentioned EXIF data a couple of times – it might be a good idea to spend some time explaining what it is… Back in the point & shoot film days it was not unusual for cameras to print the date in the viewing area of the film: (Photo Credit – Anne Guido) The advantage – you knew when the photograph was taken and, if you kept good notes, could figure out where you were that day and be able to identify the location. The disadvantage – You end up with numbers in all your photographs! Some of the pro cameras provided solutions – I used a MF-23 Data Back with my Nikon F4 that, among many functions, was capable of printing all kinds of data about the image either in the picture area or in the space between frames on the film. Of course when printing the data between frames & working with slides, you had to peal open slide frames to see the data, but at least it didn’t have to be part of the picture.

With digital cameras, if you are willing to have slightly larger files, you can record an incredible amount of information about each image. EXIF stands for Exchangeable image file format. Originally developed in the 90’s, the information format is used by the manufacturers of most digital cameras. Although version 1.0 was published in October, 1996, and the format has been revised a couple of times with the last revision – version 2.2 published in 2002, the format is not an official standard. This creates a few problems – see the EXIF link above for a description of some of them.

The most difficult problem is the way the data is stored within the image file. Unless the editor or EXIF reader you are using knows where the manufacturer of the camera put the information, it may not be able to find all or even any of it. Some of the more popular file formats, including RAW are not supported by the format so each manufacturer has to decide how to include the information. Even worse, when saving an edited image is is possible the editor will strip out the EXIF information and not save it with the saved version of the image. Some software such as Photoshop will strip the EXIF information when using “save for web & devices” but leave it under a normal save. It is up to the user to determine how the editor he or she is using will keep or dump the EXIF data during a save. For example, the image below has the most of the EXIF data stripped when blog.rv.net resized the photo to “medium” size. To see the EXIF data you must download the linked larger version of the image obtained by clicking on it.

Each viewer presents the information is its own way. Some is far more clear than others – I’ll show some samples from the following image:

First a text dump of the EXIF file:

Filename = /Users/jv/Desktop/adk2007-8453.jpg
Exif.Image.Make = NIKON CORPORATION
Exif.Image.Model = NIKON D200
Exif.Image.XResolution = 72/1
Exif.Image.YResolution = 72/1
Exif.Image.ResolutionUnit = 2
Exif.Image.Software = Ver.2.00
Exif.Image.DateTime = 2007:10:26 16:05:41
Exif.Image.ExifTag = 198
Exif.Image.GPSTag = 700
Exif.Photo.ExposureTime = 18/10
Exif.Photo.FNumber = 13/1
Exif.Photo.ExposureProgram = 3
Exif.Photo.ISOSpeedRatings = 100
Exif.Photo.ExifVersion = 48 50 50 49
Exif.Photo.DateTimeOriginal = 2007:10:10 11:22:50
Exif.Photo.DateTimeDigitized = 2007:10:10 11:22:50
Exif.Photo.ShutterSpeedValue = -847997/1000000
Exif.Photo.ApertureValue = 7400879/1000000
Exif.Photo.ExposureBiasValue = 0/6
Exif.Photo.MaxApertureValue = 30/10
Exif.Photo.MeteringMode = 5
Exif.Photo.LightSource = 0
Exif.Photo.Flash = 0
Exif.Photo.FocalLength = 170/10
Exif.Photo.SubSecTimeOriginal = 00
Exif.Photo.SubSecTimeDigitized = 00
Exif.Photo.SensingMethod = 2
Exif.Photo.FileSource = 3
Exif.Photo.SceneType = 1
Exif.Photo.CFAPattern = 2 0 2 0 1 0 2 1
Exif.Photo.CustomRendered = 0
Exif.Photo.ExposureMode = 0
Exif.Photo.WhiteBalance = 0
Exif.Photo.DigitalZoomRatio = 1/1
Exif.Photo.FocalLengthIn35mmFilm = 25
Exif.Photo.SceneCaptureType = 0
Exif.Photo.GainControl = 0
Exif.Photo.Contrast = 0
Exif.Photo.Saturation = 0
Exif.Photo.Sharpness = 0
Exif.Photo.SubjectDistanceRange = 0
Exif.GPSInfo.GPSVersionID = 2 2 0 0
Exif.GPSInfo.GPSLatitudeRef = N
Exif.GPSInfo.GPSLatitude = 44/1 649/100 0/1
Exif.GPSInfo.GPSLongitudeRef = W
Exif.GPSInfo.GPSLongitude = 73/1 4186/100 0/1
Exif.GPSInfo.GPSAltitudeRef = 0
Exif.GPSInfo.GPSAltitude = 378/1
Exif.GPSInfo.GPSTimeStamp = 15/1 22/1 2900/100
Exif.GPSInfo.GPSSatellites = 06
Exif.GPSInfo.GPSMapDatum = WGS 84
Exif.GPSInfo.GPSDateStamp = 2007:10:10
Iptc.Application2.RecordVersion = 2
Iptc.Application2.Keywords = Adirondack 2007

The information is all there, but not all that clear. For example, what is an “Exif.Photo.ShutterSpeedValue = -847997/1000000”? It isn’t the shutter speed which is listed as Exif.Photo.ExposureTime = 18/10 which, with a bit of math comes out to 1.8 seconds. It is a good thing most of the viewers offers a simplified version of the information. For those of you that really want to get into the meat of EXIF, a PDF of the current version 2.2 is available as a 752K download.

The basic camera data when viewed with Photoshop:

There are two sets of Camera Data in the Photoshop EXIF information, and like most viewers, the information is what ever part of the entire file Photoshop decided to include.

The first one (Camera Data 1) contains the most useful information, including the specific lens used to take the photograph as well as what focal length (if it is a zoom lens) it was set at.

EXIF Viewer (the other example I show next) does not give the lens information other than the focal length used for the image.

On the other hand, Photoshop only provides the GPS information if the user goes to the advanced>EXIF menu and does not include links to mapping programs.

Using EXIF Viewer within Firefox 3.0:

Notice that with the EXIF Viewer data, the GPS information is displayed along with links to Google maps, Yahoo & Mapquest, and if your have it on your computer, Google Earth. By clicking on the map link you can see the exact location where the camera was when the exposure was made. Again, that information (without the maps) is available in Photoshop if you go to Advanced>EXIF.

You might also note that the time on my camera clock and the GPS don’t agree with each other (they are off by 21 seconds). As I mentioned in my article on “Toys for the Photographer, Part 1“, if you are going to use syncing software rather than a built in or attached GPS to add location tags to your images, it is important that the two are set to the same time. Since a typical GPS clock is accurate to within a few nanoseconds, use it to set the time on your camera. Again, if you are going to use software to link a track from your GPS to your EXIF files, you may want to reset the camera clock at the beginning of each day of shooting.

I’ve listed some software below that can be used to view EXIF information. There are many more available, but these are some popular applications & add-ons.

Software:

You don’t need dedicated EXIF viewing software – In Windows XP and later Microsoft operating systems, a subset of the Exif information may be viewed by right clicking on an image file and clicking properties; from the properties dialog click the Summary tab & in the Macintosh OS basic EXIF information is available by highlighting the file & doing a “Get Information (Command I) or, for detailed information, opening the image with Preview & going to “Get Information” (Tools>Get Info>Details).

Most dedicated software usually presents the information more clearly:

Opanda IExif – A popular free viewer for Windows. They also provide a free extension for Firefox (including 3.0) that works from within the browser.
If you are using Firefox as your browser, EXIF Viewer is a useful Add-on, works with version 3.0 & is available for both Windows & Macintosh.
A stand alone EXIF viewer for either Windows or Macintosh is Reveal.
Picasa – An excellent Windows only editor available for free from Google, Picasa includes an EXIF viewer. By the way there is a rumor that a Mac version is in the works!
Although expensive, if you do alot of editing, Adobe Photoshop includes an EXIF viewer as does the less expensive Photoshop Elements. Either is available in Windows or Macintosh operating systems.

If you want to explore EXIF, be sure to download more than one of these – they each present different information in different ways – you need to try more than one to determine which best meet your needs.