I've begun early experiments in converting from Aperture to Apple photos. I've not found any good user descriptions of the process. This post will be updated as I do experiments or use the results of experiments to refine my searches.
For my first trial I created a new project from a single JPG image and one version using Aperture under Mojave. I copied it to an Intel Air running Monterey 12.1 and opened it in Photos.
Photos said it could not open the Aperture library. It did not say why.
I then regenerated full sized previews per Apple's directions and I tried again. This time the import proceeded. I could see the Version of my original photo but not the original. I then chose Revert to Original and Photos displayed the original image. Then I tried "Undo Revert" but that did nothing. My Version was lost.
Opening the package I could see a file in the originals folder named with a GUID and a .jpeg extension. It had a size of 2.3MB which is the size of the Aperture original.
I tried to repeat the process but Photos declared that "the content of the Aperture library ... has already been migrated to Photos". The famous léonie of Apple forums explained - the conversion process changes the extension to "migratedphotolibrary", I renamed the extension to .photolibrary and I was able to repeat the import process.
On repeating I saw my Version image. I then tried to edit it and got this message:
"Cannot Start Editing Photos cannot edit this image because it uses an unsupported format"
I explored the new Photos library (Package Contents) and could not find any JPG other than my original. I am puzzled as to how Photos generated the version I could see.
There does not appear to be any way to see the original image other than by reverting to original -- which cannot be undone. There also doesn't seen to be any indication that an original exists! (This appears to be a global Photos problem however).
If one wanted to see both a Version and the Original one would need to export from the Version rendering then open that in Preview, revert to Original, then compare.
I finally resolved the stacks Aperture created when I migrated from iPhotos (original image and iPhoto edited). The trick was to find all photos with keyword iPhoto Externally Edited (or similar) then save them to an album then in that album remove any that weren't stacked then unstack, delete externally edited, and re-edit originals (non-destructive).
Then I did "Reprocess Originals" for about 8000 raw images; about 6,000 were reprocessed and about 2,000 didn't need it. That leads Aperture to slowly regenerate previous/thumbnails. It's been about 24h and that is mostly done, I find that I have to periodically pause the task then restart Aperture (or my laptop) and resume. If I really need to regenerate all full sized previews that processing may take a week or so.
The Generate / Update Previews mystery
Apple's Published Recommendation (for Mojave)
Choose Aperture > Preferences, click the Previews tab, then change the Photo Preview setting to Don't Limit. Close the preferences window.
From the list of projects in the Library inspector, select all of your projects. For example, click the first project listed, then press and hold the Shift key while clicking the last project.
Click the Browser layout button in the toolbar, so that all photos are shown as thumbnails.
Choose Edit > Select All to select all of your photos.
Press and hold the Option key, then choose Photos > Generate Previews.
Aperture now generates full-size previews for every photo in your library. To follow its progress, choose Window > Show Activity from the menu bar. Quit Aperture when processing is complete.
Open the Photos app, then choose your Aperture library when prompted, as pictured above. If you aren't prompted to choose a library, press and hold the Option key while opening Photos. If your Aperture library isn’t listed, click Other Library, then locate and choose your library.
In my testing "Generate Previews" goes very quickly through JPEG originals. DNG images take longer. RAW images may take longer but I think previews were done when "reprocess originals" was run.
I'm going to partition my images by types (including other) to better understand this step. I think unstacking all photos is also wise.
In testing I found Photos.app (Monterey) only needs Aperture previews for edited images. I've already created previews for all RAW images. Plan is:
- Remove previews for all images without adjustments including RAW.
- Regenerate high res images for all images that have had adjustments (I already did RAW so don't need to redo those). I think quick view requires previews so I may be able to use that feature to confirm which have previews and which don't.