EXIF (Exchangeable Image File Format) data is created by your camera to describe the camera's settings and the characteristics of the image.
EXIF is a standard used by camera manufacturers to store camera-created information in each image. The Japan Electronic Industries Development Association (JEIDA) created the specification to make image files produced by digital cameras more standardized. As of this writing, the EXIF specification is getting a bit long in the tooth — it has not been updated since 2002. Figure 1 shows some of the EXIF values that are written to a Nikon D300 file, as extracted by ExifTool.
|Figure 1 EXIF information breaks down into two types: image encoding data, and camera settings data.
Image encoding data is basic information that describes how a file is encoded. This includes information about the structure of the file, the color model that’s used, as well as the resolution and pixel dimensions of the image. It also includes information about embedded thumbnails and any sound files that are attached to the still image. This stuff is used by programs to decode the image file and is pretty invisible to most users.
Camera settings data gives us functional measurements about the settings used at the time the image was shot. This includes the date and time as well as the exposure, lens and color balance settings. These settings are generally understood by imaging and DAM software, and can help organize the images. To see the whole set of EXIF data from a file, check out the video below. EXIF can also contain GPS data, which we look at over here.
Read more about GPS data
There are a number of tools available for opening images and examining EXIF. Probably the most effective is ExifTool, an open source program created by Phil Harvey. ExifTool is used by a number of other programs as an embedded utility to help decode image files. If you really want to know what’s in the file, this is the best way to lift the hood and look.
You can find ExifTool here.
|Figure 2 You can browse images with ExifTool to see all the EXIF metadata that is embedded. While ExifTool is a command-line utility (which is hard for many photographers to use), it's also incorporated into other programs. This video shows how ImageIngester Pro uses ExifTool to examine the metadata in a file.|
Although there is a specification for what EXIF is supposed to contain and how it's written, it is implemented differently in different camera models. Therefore, not every EXIF field will exist in every file, and even if it’s there, the data may not be accessible to third parties because it can’t be understood. Sometimes this is because a camera manufacturer wants to hide the information and sometimes it’s just a byproduct of the way the camera writes the file. Camera, computer, and software makers are attempting to fix this situation through the Metadata Working Group.
When Adobe Bridge sees a file with EXIF data, it pulls out everything it can understand and writes it as XMP metadata to the file or sidecar file. This duplicate of the EXIF data can make it easier for other programs to read since XMP is written in a standard way. Of course, it can also lead to data mismatches if the native EXIF and the XMP version aren’t identical. This is a very difficult situation to sort out and is probably best approached using the program ExifTool or PhotoMechanic (assuming you really want to go there.)
There are times when you might not want to share the camera-created information with the world. This might be because you consider your technique to be a trade secret or because you don’t wish to reveal information about exactly when the photograph was made. With a few exceptions, EXIF data is not editable in Photoshop or other DAM software, although it can often be stripped entirely from the file. Both Media Pro and Lightroom offer tools to strip all EXIF. There are a few freestanding EXIF utilities, such as ExifTool, that will let you change the EXIF values. The most foolproof way to hide the EXIF data from the viewer is to select the entire image, copy it, then paste it into a new image file, thus stripping the EXIF data.
In most cases, you won't want to mess with EXIF information. The most common exceptions will be correcting for an improper clock setting in the camera, and adding GPS data to an image that has none. You may be able to accomplish these tasks with your image editing software, or you may need to use ExifTool or other specialized software. The following videos show how to adjust the timestamp in an image file with a few different applications.
|Figure 3 Capture Time is one of the EXIF properties you might want to change. The following video shows how to do it in Lightroom and Expression Media (now Phase One Media Pro).|