The Exif Format in a Nutshell

By: Or Hillel

You might have heard the acronym EXIF in conjunction with digital cameras. EXIF allows for additional information such as shutter speed, aperture and resolution to be associated with a photo file. EXIF ensures that cameras can document such information while other software can read and use it. Here is how.

EXIF stands for Exchangeable Image File Format. EXIF does not define a completely new file format - in other words EXIF does not replace the familiar JPG or TIFF files. Instead EXIF defines a set of tags and semantics that can be added to existing formats such as JPG and TIFF to provide more information about the photo. For example JPG files use application marker segments to include EXIF information while TIFF files use the TIFF tag options. A more accurate description of EXIF would be an extension to current photo file formats that allows the documentation of extended photo information - so for example a JPG file can include EXIF information.

So what kind of information is recorded by the EXIF extension? It really depends on the camera that you are using. Some cameras do not use EXIF at all while most cameras record the basic settings in which a photo was taken such as aperture, shutter speed, ISO value, resolution and more.

We will not go over all the possible information EXIF can store as this is a very long list but we will go over some of the more important commonly used ones:

  • Image width / height in pixels: the number of pixels in the X and Y axis.

  • Orientation: camera position when the photo was taken. For example was the camera in landscape or portrait position?

  • Timestamp: the date and time when the photo was taken

  • Equipment Make / Model: strings that describe the equipment the photo was taken with. The make can be for example "Olympus" and the model can be for example "E-330".

  • Exposure program: camera exposure program used to take the photo such as automatic, aperture priority, shutter priority, action program and more.

  • Shutter speed / Aperture value / Focal length: shutter speed, aperture value and focal length settings for the photo.

  • Metering mode: the metering mode used when taking the photo for example: center weight average, spot, pattern and more.

  • Flash status: the status of the flash when taking the photo. Includes information such as whether or not the flash was fired, special settings such as red-eye prevention and more.
  • There are many software programs that allow you to read the EXIF associated with a photo. Exifreader is one of them and there are many more including popular photo processing programs such as Photoshop. Some software programs can also automatically use EXIF information to do some basic image processing. One common such processing is photo rotation. If EXIF camera orientation information is available then software can automatically rotate photos as required.

    EXIF is a great tool for learning how to take good photos. When viewing photos alongside with their EXIF information you can see the exact camera settings when taking the photo. This allows you to figure out why good photos look good and why bad photos look bad. You can learn which camera settings like shutter and aperture were right for one scenario and which were right for another and using this information use better settings in your future photos.

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