Bug 338753

Summary: Exif ImageDescription field is being used incorrectly
Product: [Applications] digikam Reporter: DrSlony <bugs>
Component: Metadata-ExifAssignee: Digikam Developers <digikam-bugs-null>
Status: RESOLVED FIXED    
Severity: normal CC: alan.pater, bugs, caulier.gilles
Priority: NOR    
Version: 4.2.0   
Target Milestone: ---   
Platform: Gentoo Packages   
OS: Linux   
Latest Commit: Version Fixed In: 4.9.0
Sentry Crash Report:
Attachments: Image tagged by digiKam-4.2.0

Description DrSlony 2014-09-02 17:48:46 UTC 
I had a hard time figuring out where the software chain I used in my workflow is broken. I traced it down to digiKam using the EXIF:ImageDescription field for the image description. While this seems perfectly fine, reading the Exif specification reveals that the unfortunate circumstance is that this field is actually reserved for the title!

CIPA DC- 008-Translation- 2012
" ImageDescription
A character string giving the title of the image. It is possible to be added a comment such as "1988
company picnic" or the like. Two-byte character codes cannot be used. When a 2-byte code is
necessary, the Exif Private tag UserComment is to be used.
Tag = 270 (10E.H)
Type = ASCII
Count = Any
Default = None"

One ends up with a long image description where the title should be, and when you use other software which stick to the spec this causes problems and more work.

I edited the metadata like this:
http://i.imgur.com/YF5qPP7.png

exiftool -G -s -a -m -u -args apg363.tif | egrep "Description panel|Title panel"
-EXIF:ImageDescription=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |
-EXIF:UserComment=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |
-XMP:ImageDescription=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |
-XMP:Title=Title panel.
-XMP:Description=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |
-XMP:UserComment=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |
-IPTC:ObjectName=Title panel.
-IPTC:Caption-Abstract=Description panel..ASCII   Kolor stitching | 3 pictures | Size: 599 x 512 | Lens: Fisheye | RMS: 2.23 | FOV: 73.76 x 49.34 ~ 28.90 | Projection: Planar | Color: None |

As you can see, according to the spec this is wrong, as EXIF:ImageDescription should be "Title panel."

Any chance this could be fixed in 4.3.0?

Reproducible: Always
Comment 1 caulier.gilles 2014-09-02 18:33:29 UTC 
As i know, we don't change anything about Exif comment management since a long time into libkexiv2 interface (and in whole digiKam in fact)

I suspect more a bug introduced in Exiv2 shared lib. After all this lib perform all background metadata management.

Q : what's give Exiv2 CLI tool instead to use Exiftool ?

After that, can you report this problem to Exiv2 team to check if all is right or not. They know better all standard to use about metadata.

Gilles Caulier
Comment 2 caulier.gilles 2014-09-02 18:37:23 UTC 
In other words, you want mean that in your example you want to see :

-EXIF:ImageDescription=Title panel.

Right ?

Gilles Caulier
Comment 3 caulier.gilles 2014-09-02 18:41:21 UTC 
Reading spec :

"A character string giving the _TITLE_ of the image."

Yes, this depand how you interpret "title" here.

"... It is possible to be added a _COMMENT_ such as..."

It's clear that it can be interpreted as a comment. And i think that usual people use Exif "Description" tags as a comment about the image.

Q : how other tools, which differentiate "Title" and "Comment" from GUI manage this tag exactly ? For ex, Photoshop which can be considerated as a reference here ? 

Gilles Caulier
Comment 4 DrSlony 2014-09-02 18:45:07 UTC 
LibExiv2: 0.24
LibKExiv2: 2.3.1

@ comment 1:
exiv2 -pa ~/test_images/apg363.tif | egrep "Description panel|Title panel"
Exif.Image.ImageDescription                  Ascii     168  Description panel.
Iptc.Application2.ObjectName                 String     12  Title panel.
Iptc.Application2.Caption                    String    167  Description panel.
Xmp.tiff.ImageDescription                    LangAlt     1  lang="x-default" Description panel.
Xmp.dc.title                                 LangAlt     1  lang="x-default" Title panel.
Xmp.dc.description                           LangAlt     1  lang="x-default" Description panel.
Xmp.exif.UserComment                         LangAlt     1  lang="x-default" Description panel.

I will attach the file.

@ comment 2: exactly, that is as the spec has it.

@ comment 3: I don't know what Photoshop does, I don't have it.
Comment 5 DrSlony 2014-09-02 18:46:45 UTC 
Created attachment 88530 [details]
Image tagged by digiKam-4.2.0
Comment 6 DrSlony 2014-09-02 18:59:59 UTC 
Reported: http://dev.exiv2.org/issues/985
Comment 7 caulier.gilles 2015-01-28 06:51:43 UTC 
Dr Slony,

What we can conclude following review by Exiv2 team from bug 985 ?

Gilles Caulier
Comment 8 DrSlony 2015-01-28 09:49:45 UTC 
Caulier: I'm actually not sure as far as Exif.ImageDescription is concerned. I asked Robin if he could clarify:
http://dev.exiv2.org/issues/985#note-19
Comment 9 Alan Pater 2015-03-06 19:40:46 UTC 
Robin Mills over at exiv2 concluded that Adobe applications DO NOT USE the Exif.ImageDescription field. For Title Adobe uses: xmp.dc.title.

MWG (Metadata Working Group) guidelines map Exif ImageDescription, IPTC Caption, and XMP (dc:description) together as "Description: the textual description of a resource's content. Also known as "user comment”, "caption”, "abstract” or "description”."

i vote for following the MWG guidelines.
Comment 10 caulier.gilles 2015-03-06 19:45:02 UTC 
Alan,

This is how digiKam work currently now (following MWG rules), or i missing something ?

Gilles Caulier
Comment 11 Alan Pater 2015-03-07 03:21:35 UTC 
Yes, agreed. Digikam is following the MWG guidlines.