Notes on Merging Photos Libraries
When merging two photo libraries we usually want a lossless merge:
- The original photos and the edited versions should be merged into the merged library as master-version pairs, so it will be possible to revert edited photos to the original.
- The library structure with albums, smart albums should be preserved in the merged library.
- All metadata, including the faces labels should be migrated.
- The products (books, cards, calendars, slideshows) should be migrated.
Written for Photos 2.0 on macOS 10.12.4 or older:
There is currently no completely lossless way to merge Photos Libraries, because Photos does not support importing one Photos Library into another library. All work-around methods are compromises. There is no lossless merging of Photos Libraries other than iCloud Photo Library, and even the merging in iCloud will not include the faces albums and the print products.
If you are planning to migrate your photo libraries from Aperture or iPhoto to Photos and own Aperture 3.6, merge your libraries in Aperture before the migration while you still can use Aperture as described here: Aperture 3.3: How to use Aperture to merge iPhoto libraries - Apple Support
Make backup copies of the libraries before you try that.
The options in Photos are:
- Merge the libraries in iCloud by uploading them to the same iCloud Photo Library: Merging in iCloud is the only way to preserve the master-version pairs, so you can revert edited photos to the original versions. Your albums and folders will migrate, keywords, titles, and other metadata. All edited images will be paired with their originals, so you can undo the edits and revert to the original. The searchable faces names will upload (only on Photos 1.5 or older, not on Photos 2.0), but not the faces thumbnails and albums. Photos will scan for duplicates while merging. It is the best way to migrate libraries you invested much work into, but uploading large libraries to iCloud requires a paid subscription for more storage than the free 5GB - for at least a month, and it is slow. My library with 40000 photos took a full week to upload.
- To merge in iCloud enable the smaller of the two libraries as your iCloud Photo Library.
- Wait for all photos to upload; that can take a very long time, a week ore more, depending on the size of the library. Photos will merge the the library into the library that is already in iCloud.
- Now enable the larger library as your iCloud Photo Library. This library will be merged into the library in iCloud too, creating a merged library in iCloud. The merged library will sync back to your larger Photos Library. The merge will not include the Faces albums and projects from the first library you uploaded. That is why I recommend to start with the smaller library. The download will be like to a different Mac, see: Use Photos and iCloud Photo Library on multiple Mac computers - Apple Support
- To sync the faces names with iCloud Photo Library, I apply keywords with the names of the persons to all photos in a people album.
- Merge the libraries by exporting the photos (edited versions and originals) from one library and reimporting them into the other library. This is the most tedious way and only feasible for very small libraries. You would have to export the edited versions and the originals separately and they would no longer be paired. On Yosemite or El Capitan - even if you export the originals with XMP sidecar files to preserve the IPTC metadata, the metadata from the sidecar file will not be applied to the originals when reimporting. Your metadata will be gone, unless you export the edited versions as JPEGS. So there is no help for it but to export both, the originals and the edited versions, and to deal with the duplicates. Photos 2.0 on Sierra can read the sidecar files on import - so exporting with XMP files will transfer the metadata to the new library.
You will have to recreate the albums as well.
- Merge the libraries with PowerPhotos: PowerPhotos is a tool to manage Photos Libraries. You can easily browse libraries in turn and move photos between libraries. Merging with PowerPhotos is fast (https://www.fatcatsoftware.com/powerphotos/. It will migrate the metadata and the albums, but you have to decide, if you want to use the originals or the edited versions. So you will either lose the editing work or the high quality originals or create redundancy by merging twice in two passes, once to transfer the originals, and then the edited versions. You will have to add a pass to remove duplicates afterward. See chapter six in the PowerPhotos manual: : https://www.fatcatsoftware.com/powerphotos/Help/merging%20libraries.html
- Another option would by to keep both libraries separate and use PowerPhotos to browse the libraries and to transfer selected albums as you go.
iCloud Photo Library would be the best option. Merging with PowerPhotos the second best.
Update for Photos 3.0 on macOS 10.13:
Photos 3.0 will also sync the recognized faces when you merge two Photos 3.0 libraries in iCloud. projects do still not sync to iCloud.