Hi,
This is my proposal for metadata handling.
Requirements:
- metadata go with the image, preferably in the image
- no data loss, no legacy data loss
- automatically migrate legacy data to XMP
- XMP sidecar can override exif values stored in unwritable raw file
- cooperation with metadata editors that don't support XMP
- preserve originals
- handle photos on read-only filesystems reasonably well
reading algorithm:
1. read exif, iptc and XMP from the file
2. now we have "unprocessed" data -> show them in "advanced exif"
3. for files with empty XMP look for sidecar, use it if
Xmp.crs.rawfilename matches
4. sync XMP with exif and Iptc using Exiv2 convert API
- detect which of Exif and Xmp.exif is newer and copy the data
in appropriate direction
- detect which of Iptc and Xmp is newer and copy the data
in appropriate direction
5. read internal database (text files for now, real database later) and
add tags that are missing (data from database should not overwrite
existing tags from file)
6. now we have "processed" data - use them in everything except
"advanced exif"
7. grouped files handling (raw + jpeg): description tags (keywords,
comments, whole iptc) are merged from all image files in the group
(a group contains the same image in various formats, descriptions
should be the same), technical tags (exif) are handled separately
for each file
writing algorithm:
- geeqie updates "processed" XMP tags
- description tags (keywords, comments) are written to all image files
in a group (raw + jpeg)
- technical tags (exif orientation) is written to each file separately
- writing can possibly copy files, thus it should use write-back cache
and run in backround
1. update exif and iptc from XMP
(for example Exif.Image.Orientation is updated from Xmp.exif.orientation)
2. try to write exif, iptc and XMP to the file if it supported by exiv2
- there should be a "backup" option - if it is enabled and no backup file
exists yet, the original is reamed to *.backup and the metadata are
written to newly created copy of the file - that preserves original files
and helps with handling of read-only files in rw dirs
- another option would make sense for writting legacy iptc block -
possibilities are:
write always, only update existing, delete iptc if exists
3. try to write XMP sidecar for raw file if step 2 was not successful
4. write XMP metadata to internal database (text files for now)
internal database:
Geeqie now uses text files for storing keywords and comments. This format
should be used only for compatibility and when the XMP via Exiv2 is not
available. Maybe we could drop write support completely.
Recommended format for internal database should be XMP, stored either in
standalone files or in a "real" database with indexes for faster searching.
The required functionality is available with Exiv2 0.17 and newer. With older
versions the metadata will be written only to internal database (text files).
See also:
http://exiv2.org/metadata.html
http://exiv2.org/doc/classExiv2_1_1Converter.html
Vladimir
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