Here are some facts about Exif, from the standards and elsewhere, that I will not be covering in tomorrow’s presentation, due to time, mostly:
- There is an entire page in the standard dedicated to “equivalent expressions” of the verbs used in the standard. For example, “shall” is equivalent to “is mandatory”. I once had to revise an entire standards of dissertation formatting because I got tired of explaining to people that the “may” in “the student may follow these guidelines” was the same as the “may” in “the student may graduate”: You don’t technically have to, but if you want your degree, you have to.
- Great warning from the wiki page: “Photo manipulation software sometimes fails to update the embedded thumbnail after an editing operation, possibly causing the user to inadvertently publish compromising information.” I want to add an ellipsis after “publish” and read the whole thing in a British accent: “to inadvertently publish… compromising information.” “You don’t say, Jeeves! Aunt Agatha will go apoplectic when she sees that thumbnail!”
- There is an element that lets computers know from which corner of the screen to start counting the rows and columns in an image.
- Exif comments tend to be different than other image metadata comments because you start by declaring your character set. Exif understands “ASCII”, “JIS”, and “Unicode”. “JIS” is used in Japanese text, which makes sense, considering who made the standards.
- There are elements which allow users to define exactly where the main subject is in the picture, by defining an invisible circle or rectangle around it.
- The GPS elements for latitude and longitude use three rational numbers each (six whole numbers, each pair being the numerator and denominator) for the degrees, minutes, and seconds. This means that, if the latitude is 34° 12′ 15″, then you can use 34/1, 12/1, 15/1. However, if your GPS unit doesn’t use seconds, but decimal minutes, like 34° 12.25′, then you can say 34/1, 1225/100, 0/1. It’s rather elegant.
- Elements in INFO list blocks can be intriguing, especially the ones not used by Exif audio files. There’s “archival location,” “medium,” “product” (what product the image was originally intended for).
- There is a tag to let camera manufacturers note whatever they feel like noting. The wiki article warns that, sometimes, the manufacturers are happy to encode that information.