I decided to revisit an old bug that I logged about a prob­lem I have with f-spot han­dling of exif head­ers. Now I’m more con­fused than ever. I can see what’s hap­pen­ing, but not how or why.

The prob­lem I’m hav­ing is that when I upload some pho­tos to gallery web­sites the han­dling of exif data doesn’t appear con­sis­tent. For exam­ple, have a look at this photo. If you look at the right hand side of the screen where the photo title is shown it also shows the cap­tion. It looks like this:

Now have a look at the same photo uploaded to pica­s­aweb (the sizes are slightly dif­fer­ent — I think pica­s­aweb changed them on the fly when I uploaded via google plus). In this case there is no gar­bled text and pica­s­aweb has used the exif descrip­tion field for the photo cap­tion. i.e:

So what’s hap­pen­ing here? Well, here’s what I think is hap­pen­ing. Pica­s­aweb is extract­ing the cap­tion from the exif field Description, and Zen­fo­lio is extract­ing the cap­tion from the field UserComment. Here’s what I get if I run exiftool on the image file (you might need to click on the image to see it properly):

As you can see the User­Com­ment field con­tains gar­bled characters.

A lot of my pho­tos have this and the incon­sis­ten­cies can cause me headaches. I decided on a brute-force scan of my photo col­lec­tion to address the issue. I thought, why not just dupli­cate the Descrip­tion field into the User­Com­ment field? That way, what­ever pack­age or gallery reads the image file will prob­a­bly get the cap­tion. So here’s the script I used:

#!/bin/bash

#
#       Process all jpegs and overwrite UserComment field with Description
#       field where they differ.
#
find /jpegs -type f -iname '*.jpg' | while read fname
do
        field_usercomment=$(exiftool -UserComment "${fname}" | sed 's/^.*: //')
        field_description=$(exiftool -Description "${fname}" | sed 's/^.*: //')

        if [[ "${field_usercomment}" != "${field_description}" ]] ; then

                echo "$fname"
                echo "User Comment: ${field_usercomment}"
                echo "Description: ${field_description}"
                echo

                echo "${fname}"
                exiftool -overwrite_original -UserComment="${field_description}" "${fname}"
                echo
        fi
done

After a sat­is­fy­ing hour or two my pho­tos all looked a bit tidier. So now I have a cludge — some­thing that will get round the prob­lem. But I’d really like to treat the cause, and not the symp­tom. So what’s the cause?

My first guess has always been the cam­era. I have a knack­ered old Nikon Coolpix that gives me prob­lems. But I see this prob­lem with other cam­eras too, my Canon DSLR and com­pact cam­era have acquired the gar­bled field in some pic­tures too.

So I turn to f-spot, the photo-management soft­ware I use in Linux Mint. I checked the exiftool out­put from a test file, then imported it into f-spot. I then added a tag so that f-spot would write out the exif data (I have f-spot con­fig­ured to Store Tags and Descrip­tion inside image files where pos­si­ble) then had a look at the image file. Here’s what I got:

The out­put from the first invo­ca­tion of exiftool is on the jpeg before import­ing into f-spot. The sec­ond exam­ple shows the out­put of exiftool run on the file after it has been imported into f-spot. It looks like f-spot does some­thing to the image that man­gles the UserComment field.

At this point I assumed (erro­neously I think) that f-spot must be stor­ing the UserComment and Description fields in its sqlite data­base. Using sqlite3 on the com­mand line I had a look at the struc­ture of the pho­tos table:

dougie@phoenix ~ $ echo '.schema photos' | sqlite3 .config/f-spot/photos.db
CREATE TABLE photos (
    id            INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    time            INTEGER NOT NULL,
    base_uri        STRING NOT NULL,
    filename        STRING NOT NULL,
    description        TEXT NOT NULL,
    roll_id            INTEGER NOT NULL,
    default_version_id    INTEGER NOT NULL,
    rating            INTEGER NULL
);
dougie@phoenix ~ $

There’s the description field, but no UserComment field. But it looks to me that f-spot is cer­tainly writ­ing to the UserComment field when it updates an image file. Per­haps it’s depen­dent on the type of con­tents of the Description field. It doesn’t, how­ever, make any dif­fer­ence as far as I can tell what the con­tents of the Description field are. In this exam­ple the text ends with an excla­ma­tion mark, but I can’t detect any pat­tern in the text I put in Description fields that might pro­vide a clue.

So if f-spot isn’t stor­ing the UserComment field directly what, when, and why is it writ­ing to the field in the image file? It seems that here we enter the murky world of XMP and I rapidly lose the ten­u­ous grasp I had on the under­ly­ing tech­nol­ogy up to this point.

Back in 2008 there was a dis­cus­sion on the f-spot mail­ing list about how f-spot stores its data in the image file. Re-reading that thread it sounds as if f-spot writes its tags to the XMP meta­data and not all util­i­ties are able to read that. This was 2008 mind, and f-spot has jumped a few ver­sions since then.

Out of the same thread came a hint on using exiv2. This is a tool I use a lot, espe­cially for adjust­ing ‘date taken’ time­stamps, but hadn’t found it any use for extract­ing the UserComment field. It turns out I hadn’t RTFM prop­erly and it is pos­si­ble if you tell exiv2 to look at XMP data. This leads to some inter­est­ing out­put. Here is the exam­ple file again, using both exiv2 and exiftool to exam­ine the field contents:

dougie@phoenix ~ $
dougie@phoenix ~ $ exiftool -UserComment -Description /jpegs/2011/07/17/test1.jpg
User Comment                    : 桷⁹畲污湯⁧桴⁥敢捡⁨桷湥礠畯挠湡挠瑵琠敨挠牯敮ⅲ††††††††††††
Description                     : why run along the beach when you can cut the corner!
dougie@phoenix ~ $
dougie@phoenix ~ $ exiv2 -p a /jpegs/2011/07/17/test1.jpg
Exif.Image.ImageDescription                  Ascii      77  why run along the beach when you can cut the corner!                        
Exif.Image.Software                          Ascii      21  f-spot version 0.8.0
Exif.Image.ExifTag                           Long        1  162
Exif.Photo.DateTimeOriginal                  Ascii      20  2011:07:17 09:37:13
Exif.Photo.UserComment                       Undefined  84  why run along the beach when you can cut the corner!                        
Exif.Image.GPSTag                            Long        1  296
Exif.GPSInfo.GPSVersionID                    Byte        4  2.0.0.0
Exif.GPSInfo.GPSLatitudeRef                  Ascii       2  North
Exif.GPSInfo.GPSLatitude                     Rational    3  55deg 32' 25.410"
Exif.GPSInfo.GPSLongitudeRef                 Ascii       2  West
Exif.GPSInfo.GPSLongitude                    Rational    3  1deg 37' 58.960"
Exif.GPSInfo.GPSAltitudeRef                  Byte        1  Above sea level
Exif.GPSInfo.GPSAltitude                     Rational    1  9.5 m
Exif.GPSInfo.GPSTimeStamp                    SRational   3  09:37:13
Exif.GPSInfo.GPSMapDatum                     Ascii       7  WGS-84
Exif.GPSInfo.GPSDateStamp                    Ascii      11  2011:07:17
Xmp.xmp.CreateDate                           XmpText    19  17/07/2011 09:37:13
Xmp.xmp.Rating                               XmpText     1  0
Xmp.xmp.CreatorTool                          XmpText    20  f-spot version 0.8.0
Xmp.dc.description                           LangAlt     1  lang="x-default" why run along the beach when you can cut the corner!                        
Xmp.dc.subject                               XmpBag      2  Dougie Nisbet, Coastal Run - 2011
Xmp.exif.UserComment                         LangAlt     1  lang="x-default" why run along the beach when you can cut the corner!                        
dougie@phoenix ~ $

Inter­est­ingly, exiv2 is dis­play­ing the UserComment data in clear text, in two places, which I’m guess­ing must be some­thing to do with the dif­fer­ent types of meta­data — XMP and EXIF.

So does this mean this has noth­ing to do with f-spot at all? If exiv2 is able to read the text, per­haps it’s some­thing to do with the util­ity used to exam­ine the image file? If I have a look at the file using gee­qie and open up the EXIF win­dow geeqie seems to under­stand the text too:

Per­haps this is an unre­lated set­ting I need to have a look at. Lan­guage, Locale, who knows. The issue seems to crop up in dif­fer­ent places so it may very well be unre­lated to f-spot. For the time being I have a fairly straight­for­ward work-around, I just need to remem­ber to run a script to copy the descrip­tion field into the UserComment field for any images I update in f-spot. It’s a bit of a nui­sance but fairly easy to auto­mate, and a lot less time-consuming than try­ing to get to the bot­tom of the mystery!