Tagging your images is so cool, compared with using plain old folders…at least that’s what everyone seems to say. But how do your carefully created keywords get attached to your images? What are EXIF, IPTC and XMP? And most of all…why should you care about all of these acronyms? Understanding the different types of image metadata will help you better manage your pictures. Read on to find out what happens behind the scenes of your image tags.
Why is image metadata cool?
Image metadata in general is defined as “data about data”. In particular, image metadata is information about a specific picture. There are two types of image metadata: technical information about the image and information about the contents of the image. I usually refer to these two types as: technical information and content information. Technical information contains things like: camera type, ISO speed and aperture value. This type of information is created by your camera each time you take a picture. Content information, on the other hand, contains things like: subject, country, category and keywords. Content data is created by you, the photographer, since you’re the only one who can provide content data.
The easiest way to distinguish between different types of image metadata is to think about who needs to create each type. Technical information about an image (EXIF) is created by the camera, while content information (IPTC/XMP) is created by you, the photographer.
What about all these names like: EXIF, IPTC, XMP?
All of these names represent standards for saving technical and content information about images. They are essentially standards for data portions that can be added to image files. While EXIF and IPTC have been designed specifically for image file types (.jpg, .gif, .tiff), XMP data can be embedded in multiple document formats including PDF. Because XMP (developed by Adobe) is newer, it has been developed as a super set (that means that it contains) of IPTC core elements. This means that software usually can save content information in both formats.
Here is an easy way to remember how these names are being used: EXIF is the standard for representing technical information about an image while IPTC and XMP are standards for representing content information about an image. The first is created by the camera while the second by humans.
EXIF contains technical characteristics of the picture
EXIF contains information generated by your digital camera each time you take a picture. It contains technical information about the picture itself like:
- Date picture taken
- ISO speed
- Aperture value
- If the flash fired or not
As you can see, this type of information is generated by your camera and represents all the technical characteristics of your picture. However, it does not contain any information about the contents of your picture. Also, another characteristics of EXIF data is that you are not supposed to modify it. There is software that will allow you to modify EXIF data, but this data is not intended to be modified. It doesn’t really make sense to change it anyway since it is generated by your camera.
IPTC contains information about the contents of the picture
IPTC contains information created by the photographer and entered into the IPTC fields using some software program. The key difference is that the information contained in the IPTC fields represents information about the content of the picture. It is obvious that a camera would have no idea about the subject of the picture, so there is no IPTC metadata in any pictures when you shoot them. Your camera knows nothing about IPTC…and it shouldn’t anyway. Here are some examples of IPTC metadata fields:
- Category – a list of preset categories
- Additional Category – this is free form and you can add text in here
- Keywords – this is where you place your keywords. This is probably the most widely used IPTC field
Again, as you can see, this data is about the content of the picture and you alone as the photographer can enter this data. This is where you need to use software like: Adobe Lightroom, iTag, iMatch, ACDSee Pro and others to manipulate the IPTC information for your pictures. Once you add this information in your software you have to make sure you save it to each image file. Otherwise all this information will stay only in your software.
What’s the point of all this image metadata acronyms?
Again…let’s recap: EXIF contains technical information about a picture while IPTC (and XMP) contains information about the content of a picture. Remember that this information is saved as part of your image file. This means that your image file size will increase…very little though because this information is simple text. The whole point of saving metadata along with each image is to provide information about the image: both technical and content information. So, when your image “travels”, the information about the image “travels” with your image file.
Do you really need to save metadata?
Why would you need them when you can have all this information stored in your software? Well…it’s pretty simple. If you don’t save all this information with each picture, then nobody else but you (using your software) would be able to see this information. If you don’t care about the portability of your metadata (including keywords), then you don’t really care about IPTC (or XMP for that matter). But if you want to pass your pictures to news agencies or most photo sharing websites, you need to do this because they will want to know information about the content of your pictures without having to open and view each picture. This is it on this subject…at least for now.