Data about data

You’re sure to come across metadata while editing images, this should help it make more sense.

What is Metadata

Information attached to an image or file, just like we used to write names, places or dates on the back of a photograph.

Types of metadata

EXIF – Usually written by the camera, mostly about the capture conditions like shutter speed, date taken or camera settings.

IPTC-IIM – Mostly about the contents of an image, ratings, keywords, ownership and rights.

XMP – The latest way to store metadata, XMP was created to overcomes some limitations of the IIM and EXIF data format.  The XMP block can include just about anything including EXIF or IPTC fields, it’s often used to record proprietary information, such as the adjustments made to an image using photo editing software like Lightroom.

Where is the metadata?

An image file contains several blocks of information:  EXIF, IIM, XMP and the IMAGE data itself.  To make things even more confusing, the XMP block can be stored in a separate file which sits next to the image, rather than in the image itself.  These sidecar files have the extension .xmp and if you open them with a text editor you’ll see they usually contain a list of settings and other information.

Previously, the IPTC data like keywords would be found in the IPTC-IIM block, but that’s now considered out dated, because the 90’s were just so long ago :).  IPTC data should now be stored in the XMP block, or preferably both for maximum compatibility, hopefully your software knows this.

Metadata confusion

Because some software doesn’t doesn’t read every block, or may prioritise one block over the other, metadata can appear to change or disappear because its been written to a different block than the one your software is displaying.

Here’s an example of how metadata can get mixed up when using different software.  Apply a star rating to an image in Bridge and then change the rating with the image in Capture One.  Bridge won’t recognise the Capture One rating because it’s been applied in a sidecar file which Bridge won’t read, so the rating you see can depend on the preferences used in either application.  This sort of thing happens across a lot of  different applications, but that doesn’t mean they are non-compliant with the standards, they just use them differently and perhaps in ways that aren’t always ideal.

Be aware

Metadata may not be as straight forward as you think, so when strange things happen you’ll need to dig deeper.

As I wrote this article I’ve had some had some correspondence with Carl Siebert, an expert in all things metadata, find him here if you want to dig deeper.

John Hardiman