Hidden in the EXIF
When you take a picture, the camera stores a lot of settings in the image file. This information, called the EXIF data can be retrieved by most of the better image viewers (and some browser plug ins) but only a few of these show all the information. This article will look at some of the more useful bits of information that you may not know you have. To do so we'll use exiftool, a freeware exif reader that shows almost all the exif tags there are.
Basic image parameters
These are shown by almost all image viewers with EXIF capability. The tag names may differ depending on the software you're using, but they should all be there (and many more on top).
| Tag | Exiftool tag | Description |
|---|---|---|
| Image Width | Imagewidth | The width of the image in pixels |
| Image Height | ImageHeight | The height of the image in pixels |
| Caption | ImageDescription | A user-settable caption for the image. Olympus cameras always set this to OLYMPUS DIGITALCAMERA, which might get displayed by some online galleries which use this value to set their captions. In those cases you may want to use an exif editor to change it. |
| Make | Make | The camera brand. For olympus cameras this is OLYMPUS IMAGING CORP. |
| Model | Model | Camera model. E.g. E-3 |
| Artist | Artist | The photographer. This is left blank by olympus, but you may want to set it with an exif editor. |
| Copyright | Copyright | As above |
| Date/Time Original | DateTimeOriginal | The timestamp the image was taken at (if your camera clock is accurate). |
So far these have not really given you too much photographic information, so let's move on to the shooting parameters.
| Tag | Exiftool tag | Description |
|---|---|---|
| F-Number | FNumber | The F-number of the apperture the image was shot with. e.g. 2.0 |
| ISO | ISO | TheISO speed rating |
| Exposure Time | ExposureTime | The exposure time in seconds (or fractions thereof). |
| Exposure Compensation | ExposureCompensation | The exposure bias you enterred when taking this shot, in eV. e.g. -0.3 |
| Max. F-number | MaxApertureValue | The largest apperture the lens was capable off at the selected focal length. |
| Flash | Flash | Whether the flash was on and whether it fired or not. |
| Focal Length | FocalLength | The focal length of the lens. This is the actual focal length in mm, to get the 35mm equivalent multiply by two as normal. |
Getting and using exiftool
For the more advanced EXIF tags we'll use exiftool. Exiftool can be found at http://www.sno.phy.queensu.ca/~phil/exiftool/ for most operating systems. It's a command-line utility, but there's also a GUI for windows if you prefer. If you want to try any of the examples provided here, you'll need to install the command-line version as per the instructions (if you're installing the windows executable, rename it to exiftool.exe).
The basic usage is simple:
exiftool Filename.jpg
Gives all exif tags.
exiftool -table -filename -FNumber -ISO -ExposureTime -ExposureCompensation -FocalLength *.JPG > Test.txt
Creates a (tab-delimited) table with the filename, FNumber, ISO rating, Exposure time, exposure compensation and focal length for every jpg file in the folder and outputs the data in a textfile named Test.txt. As you can see you can use the exiftool tagname with a dash (-) in frot of it to read it.
Olympus Metadata
With exiftool (or Olympus Master/Studio) we can get to the olympus-specific exif tags.
| Tag | Exiftool tag | Description |
|---|---|---|
| Exposure Mode | Olympus:Exposuremode | The shooting mode used (PASM) |
| Focus Mode | Olympus:Focusmode | Focussing mode (Single AF, Continuous AF, MF, ...) |
| Focus Distance | Olympus:focusdistance | Here's my personal favourite hidden exif value. This gives the focussing distance in meters. If you focussed correctly, this should also be the subject distance. |
| Noise Reduction | Olympus:Noisereduction | Whether black-frame subtraction noise reduction is on |
| Lens Model | Olympus:lenstype | The lens used for this shot |
| Extender | Olympus:extender | EX-25, EC-14, EC-20, ... |
| Metering Mode | Olympus:Meteringmode | Spotlight, Center-weighted, ... |
| Auto Exposure Lock (AEL) | Olympus:AELock | Personally I use this one to easily find quick-panoramas (which I make with AEL) I've taken |
| White Balance | Olympus:WhiteBalance2 | The white balance mode used |
| Level Gauche Roll | Olympus:LevelGaucheRoll | Amount of roll detected by cameras with an electronic level, like the E-30 |
| Level Gauche Pitch | Olympus:levelgauchepitch | Same as above, but pitch. |
Other somewhat interesting tags
| Tag | Exiftool tag | Description |
|---|---|---|
| Quality | Olympus:Quality | Image quality (SHQ, HQ, ...) |
| Scene Mode | Olympus:scenemode | Scene mode, if you use it (portrait, fireworks, etc etc) |
| Serial Number | Olympus:serialnumber | The serial number for your camera. |
| Lens Serial Number | Olympus:LensserialNumber | The serial number for the lens |
| Sensor temperature | Olympus:Sensortemperature | Can be handy to know for some noise removal techniques (hot sensor noise si different than cold sensor noise) but would be handier if the unit was given. Doesn't work for all bodies. |
| Image Stabilization | Olympus:imagestabilization | Whether IS was on and which mode was used |
