What is EXIF data?
EXIF stands for exchangeable image file format. Oh goody! Another stupid acronym to remember, the world needed more of those. And it doesn't work! It should be EIFF! Yeah but that wouldn't be quite as catchy would it?
Most modern cameras store EXIF data in every photo file they create. EXIF data is metadata, basically it stores the camera settings used to create the picture and the time and date it was created.
Here is a set of EXIF data from one of my photos, displayed in Adobe Bridge. In the top left panel are the most common camera settings that we need to know. The shutter speed and aperture, ev compensation (that's the -1 figure you can see) and the ISO setting. The right hand panel tells me the size of the file in pixels, the size of the file in kilobytes, the color space (sRGB) and the color mode (RGB).
Lower down you can see that some of this information is repeated plus the all-important date created and date modified. Cleverly the date created refers to the original RAW file and the date modified refers to the JPEG file I just created even though the JPEG has a different file name.
A note of caution for wrongdoers and people who value privacy
An increasing number of cameras and a huge number of smart phones are fitted with GPS and 'know' where you are at all times. These cameras will also record your location in the EXIF data unless you specifically turn it off. So, if you're supposed to be working late and you're really out with the boyfriend, don't take any pictures.
Moving down the list the next section, IPTC Core, contains a set of tags where you can record your own data. There are loads of slots, title of the picture, description, keywords and so on. Probably the most useful of these is the copyright tag. This enables you to stamp your name on each photo you create. Once you have stored your copyright details in Photoshop, they will appear in every file you create or edit in the program. I think it would be nice if that could be entered into the camera and the photo could be tagged as your copyright as soon as you take it but I don't know any cameras that do that yet. I certainly can't see any way to do it on my camera.
As you can see, the camera data is very comprehensive even recording the exact focal length that the zoom lens was set at. I think that section is pretty self explanatory so I won't go into details on each item.
The last section on the display contains the settings that I changed in Adobe Camera RAW. I intend to talk a lot more about ACR over the next couple of months with the aim of getting you all interested in shooting RAW files and processing them in this, very simple to use, program.
So what's it all for then?
Apart from storing this data for your own benefit, enabling you to look back and remember exactly how you took the shot, the data can be accessed by lots of different software. A typical example is the members' gallery on this site. If you click on a photo to enlarge it you will find a little camera icon under the photo. Click on this and the EXIF data is revealed for that photo. This saves the photographer having to put all the details under each picture. The the information is very useful when offering a criticism of the picture, we can avoid saying things like "you should have used a wider aperture" when we can see that the photographer was already using the widest aperture available on that lens. Alas sometimes there is no EXIF data stored, I think this occurs when someone makes a new file in a program that doesn't transfer the data. As you can see above, Photoshop and Photoshop elements certainly do retain all the data and transfer it to any new file you make.
Also, apparently, the copyright info appears on Facebook when someone posts one of your photos, although I haven't seen that myself, maybe they have stopped it.
Wrongdoers and people who value their privacy take heart
You'll be pleased to know that there are plenty of programs on the internet that will strip off the EXIF data from your files should you wish it to do so, for whatever reason.
There are many more EXIF tags for different kinds of files, audio etc. I have just mentioned the ones that affect us photographers. If you want more technical details, have a look at this wikipedia article.
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