How to get EXIF keywords using mini_magick in a Rails app?

Question

I am attempting to pull the EXIF information for images that have values for the EXIF "keywords" attribute. I have successfully read EXIF information using mini_magick by simply opening an image and using:

image["EXIF:Model"]

For some reason, none of the following will return keywords for an image that I know has them:

image["EXIF:Keywords"]
image["EXIF:XPKeywords"]
image["EXIF:Subject"]

I have confirmed that the image in question does have this information using this utility: http://regex.info/exif.cgi

Does mini_magick only have access to certain EXIF values? It seems so odd that I can access certain EXIF information but not others.

Answer 1

EXIF metadata is created by camera, therefore it contains only technical related stuff. What you actually want to access is IPTC and XMP.

Imagemagick, which is behind mini_magick, allows to read IPTC, e.g. image["%[IPTC:2:25]"] for keywords (update: be aware of perfomance issues, see comments).

As for XMP, I don't know an easy way to do this. You can try to run

`identify -verbose #{your_filename}`

and then grub lines that include xmp.

Answer 2

As Nash Bridges pointed out, I needed to actually access XMP data. I found a way to do this using two gems: exifr and xmp. After installing both of those gems, I used the following code in my controller that processes the image upload:

tags = XMP.parse(EXIFR::JPEG.new(StringIO.new(params[:file].read))).dc.subject.join(',').downcase

I was unable to find a way to do this with only mini_magick though I'm sure that it would be possible by parsing the raw data output by the "to_blob" method of a mini_magick Image model.