Metadata support for scanned images

[frli8848]

Is your feature request related to a problem? Please describe.

In 5.4.1 there is only a limited supported for adding metadata such as GPS coordinates, camera model, lens model etc. for scanned images where the image files do not have such exif data. For example, when I try to find an aperture tag in the Metadata editor settings nothing shows up. Furthermore, when searching for longitude or latitude (GPS coords.) I get something like:

Xmp.dwc.decimalLongitude     XMPText
Xmp.dwc.verbatimLongitude    XMPText

I find this a bit confusing. Why do we need to see (internal/low level) metadata tags (like the Xxmp.dwc... stuff) when we try to add tags?

Describe the solution you'd like

Add support for adding or modifying (override) tags like:

• exposure
• aperture
• lens model
• camera model
• datetime
• longitude (and make it work with the map)
• latitude (and make it work with the map)
• film stock (for example Kodak Portra 160)
• box speed (for example, ISO 160)
• exposure index/EI (for example, ISO 400)

That is, when there is an existing tag shown in the image information, such as exposure, I want to update that one and not add another one.

Suggestion: add a Scanned setting/check box somewhere which switch on the possibility to modify existing tags.

It would also be useful to have a list of film stocks (sorted by brand etc) which a user can choose from.

Alternatives

Additional context

There is a discussion here too: #19366

[zisoft]

When I started to enhance the metadata editor I first allowed to add all tags which are supported by exiv2, including exif tags.

This led to a bunch of confusion because users started to add exif tags to the metadata editor and assumed that those additional exif tags are now read from the image on import. But this is not true, the metadata editor is for export only, not for import.

To avoid such confusion the metadata editor was limited to only those tags which are clearly supposed to be user-editable.

Due to the huge amount of possible tags there are clearly some missing here, as noticed in #20264.

• exposure
• aperture
• lens model
• camera model
• datetime
• ...

These are most likely exif tags, which are not in the category of user-editable tags. Would be easy to add them back to the list of allowed tags but then we are again in the scenario described above.

[wpferguson]

This has been on my radar for awhile. My solution would be a Lua script that would:

• provide a UI to edit the image EXIF values in the database.
• provide a copy and paste function so that one image could be edited, copied, and then pasted to the rest of the images

[zisoft]

@frli8848 , @wpferguson : I think I have found a way to read user defined exif data from metadata editor on import.

This way we can re-enable to allow ALL tags which are supported by exiv2 and let the user define whatever is needed for their workflow. Maximum flexibility with metadata.

I will make some more tests and provide a PR.

[frli8848]

Is it possible to have a more higher level approach where one do not have to browse/search through all the various existing EXIF tags? For GPS coordinates, for example, it should be enough to select just longitude and latitude and not have choose between:

Xmp.dwc.decimalLongitude     XMPText
Xmp.dwc.verbatimLongitude    XMPText

etc. (I do not know the difference between them?). If one really wants to learn and select specific EXIF data tags then why not have a low-level (advanced) setting for that? Just let the high-level interface select suitable EXIF tags for at least the common cases (like the ones I listed above).

[zisoft]

If I am now going to change that, it would give complete freedom: An unfiltered list of all available tags.
You can see this dialog with the unfiltered list in the preferences of the export dialog, where you can redefine the tags at export.

That means: The user has to decide what tags to add.

Regarding the Xmp.dwc. tags you have now mentioned multiple times: They have explicitly been requested in #20264 so there is a real world use case for a user to have them in the list.

why not have a low-level (advanced) setting for that? Just let the high-level interface select suitable EXIF tags for at least the common cases

What are low-level and high-level tags? That would require to maintain a list with such definitions. What you categorize a low-level tag (like Xmp.dwc) may be a high-level tag for someone else who needs it daily.

[frli8848]

The Xmp.dwc... was just an example. What I mean is that to add basic metadata tags to an image it should not be needed to learn the exact name of the underlying EXIF tags that is stored in the file. darktable's image information does not show EXIF tags, it just says exposure 1/500 or aperture f/8 etc. I do not mean that you should remove support for adding specific EXIF tags for those who need that but I think a simpler interface, with some pre-defined and easy to understand names, is very useful.

[pehar1]

it should be enough to select just longitude and latitude and not have choose between:

Xmp.dwc.decimalLongitude     XMPText
Xmp.dwc.verbatimLongitude    XMPText

I do not know the difference between them?

See https://exiv2.org/tags-xmp-dwc.html for detailed information.

But what happens with

Exif.GPSInfo.GPSLatitude
Exif.GPSInfo.GPSLongitude

and the corresponding

Exif.GPSInfo.GPSLatitudeRef
Exif.GPSInfo.GPSLongitudeRef

suitable EXIF tags for at least the common cases

Unfortunately, there’s no such thing as “common cases.” Every camera manufacturer and every editing software can use tags however they like (and they do). The only way to reliably obtain the desired information is to analyze the image file, select the desired tags and then to provide a precise definition of the tag to be used in darktable. The approach taken by @zisoft seems to me to be the only reasonable one.

[gi-man]

I read the PR and now this Issue. Ive been thinking of any unintended consequence of allowing all tags on import. I cant think of any that are not self inflicted screw ups (eg. changing the lens description thus not matching the lens module).

[frli8848]

Unfortunately, there’s no such thing as “common cases.” Every camera manufacturer and every editing software can use tags however they like (and they do). The only way to reliably obtain the desired information is to analyze the image file, select the desired tags and then to provide a precise definition of the tag to be used in darktable. The approach taken by @zisoft seems to me to be the only reasonable one.

Yes but when you shoot analog there are no exif data at all so one (darktable) should be free to just pick a reasonable common tag for each parameter or am I missing something? This is why I suggested an "analog mode" where one, for example, just get some text boxes to fill in lens and camera model etc etc (without having to study exiv2 documentation).

Depending on how one digitize the analog images there may be some EXIF data in the files but that is just telling what equipment one used to scan the images (which also may be of interest).

[pehar1]

Even digital copies of analog photos created with a scanner contain a large number of tags. And please also keep in mind that you can digitize photos with a camera (I’ve done this with tens of thousands of analog photos), in which case the complete set of tags from the camera used is available and must be adjusted accordingly.

The approach you suggested using “common tags” would also fail at least in the second case. It would be nothing more than a specialized niche application that isn't universally functional, which would certainly lead to a significant number of new issues reported by users.

By the way: what makes it so difficult to look up the relevant EXIF documentation (https://exiv2.org/tags.html , https://exiv2.org/metadata.html) ?

[frli8848]

Even digital copies of analog photos created with a scanner contain a large number of tags. And please also keep in mind that you can digitize photos with a camera (I’ve done this with tens of thousands of analog photos), in which case the complete set of tags from the camera used is available and must be adjusted accordingly.

Yes that is I why I wrote "Depending on how one digitize the analog images ..." section above. I am not sure if these tags are very interesting to keep (they may be). Vuescan writes something like LS-5000 for my Nikon scanner and if you use a digital camera you get the exif data from that one. I think the most important metadata is what equipment one used to take the image (including film stock and settings) and where and when it was taken.

The approach you suggested using “common tags” would also fail at least in the second case. It would be nothing more than a specialized niche application that isn't universally functional, which would certainly lead to a significant number of new issues reported by users.

Hm, do you have any examples of what these issues may be? Say if you pick an exif tag for the camera model parameter which is used internally in darktable (saved in some way in the corresponding .xmp files) and possible used when exporting - how would that create issues for users?

By the way: what makes it so difficult to look up the relevant EXIF documentation (https://exiv2.org/tags.html , https://exiv2.org/metadata.html) ?

Well it complicates things for something that could be very simple.

[zisoft]

for something that could be very simple.

@frli8848 : I am really tired of this discussion.

With #20872 darktable gives complete freedom to the user to use whatever tags might be useful for their workflow.
What might be complicated for you may be a daily task for another user. And nobody will do your work just because you are too lazy to read documentation.

And as an example for GPS latitude, this is what the list gives when searching for "latitude":

Is it really too hard to think about this a few seconds and choose Exif.GPSInfo.GPSLatitude as a first try?

Just again: What might be comfortable for YOU might be a burden to others.

[frli8848]

for something that could be very simple.

@frli8848 : I am really tired of this discussion.

With #20872 darktable gives complete freedom to the user to use whatever tags might be useful for their workflow. What might be complicated for you may be a daily task for another user. And nobody will do your work just because you are too lazy to read documentation.

Is it really too hard to think about this a few seconds and choose Exif.GPSInfo.GPSLatitude as a first try?

Just again: What might be comfortable for YOU might be a burden to others.

I was just trying to suggest a way to simplify the metadata user interface for analog images to make it easier to use, in particular for newer users who may not know what exif data (and its tags) is, that darktable is using exiv2, and that you need to read exiv2's documentation.

BTW: I was involved in the exiv2 project for a short while and I have no problem reading its documentation.

I think that was my 2 cents.

[wpferguson]

I was just trying to suggest a way to simplify the metadata user interface for analog images

I still think a Lua script for this specific application is probably the best, since the information that is being supplied will go into the image database record and the formats of specific fields aren't necessarily user friendly. A script could supply combo boxes with user friendly values and generic names, then convert and store the information in the formats necessary for the image record.