This week's sponsor
Six Colors Membership - Help support us by becoming a member and get access to a members-only podcast, newsletter, and community.
By Jason Snell
September 13, 2016 10:55 AM PT
The release of iOS 10 marks the debut of a bunch of major new features to Apple’s Photos app. By far the biggest change to Photos is the addition of a comprehensive machine-learning algorithm that scans the contents of your photos to automatically identify people, objects, settings, and other items in your images without any help from you.
With both macOS Sierra and iOS 10, all the images in your Photos libraries will be scanned millions of times with machine-learning algorithms to identify faces, as well as more than 4,000 different scenes or objects. Every time you take a photo in iOS 10, Apple will scan that image for any possible information and use that metadata in several different ways. For all the photos already in your library, well—your device will need to scan them all, one at a time. That will take time and use a whole lot of processor power, so be sure to leave your iPhone plugged in overnight after you upgrade so that it can stealthily scan your photos while you sleep.
Photos exposes all the faces that it identifies via its new algorithms in the new People album. The rest of the machine-learning data is best discovered via the search box. Objects Apple identifies—including things like dogs, cows, and beaches—are organized in Categories, and you can search for them just by typing whatever you can think of. If you type dog, Photos will show you all the photos it thinks might feature dogs.
Another major addition to Photos is Memories, automatically generated collections of your photos. To create a Memory, Photos selects photos based on location, time, and even the people identified in the photos. You can tap on the header image at the top of any memory to view an automatically generated video highlight reel for that memory, a collage of audio and video clips that’s assembled by iOS. You can also tap on the clip and edit it, choosing a mood from a palette of choices such as Uplifting and Chill, and a length (Short, Medium, or Long). If you really want to go to town, you can add or omit items, pick custom music, and adjust the length down to the second.
The new Places album lets you browse all of your photos based on where they were taken. Maps are also more prevalent throughout Photos, most notably in Memories.
A new Details view lets you see more information about any given photo in your library. Open an image and then tap the Details button or just scroll. You’ll see the people Photos has identified as being in the photo, the location where the photo was taken (with an address, a map, and an option to show other photos taken nearby), a set of Memories related somehow to the contents of your photo, and even a link to see all the photos taken on that particular day.
Those “related Memories” links spread throughout Photos are cleverly generated based on the metadata gleaned from Apple’s machine-learning algorithm. An image of a baseball game offered other outings to the ballpark; an image of my mother offered collections of her various visits to our house and ours to hers.
When you’re viewing details of a photo, you can teach Photos the name of the person it detected by tapping one of the faces in the People section. Photos opens a screen for that face, with a collection of photos, related groups and people, places where that person was spotted, and related collections of photos. At the very top of that screen, tap the Add Name header and enter in the person’s name. Photos suggests names based on the Contacts list, but you can also assign a name that isn’t currently in Contacts. If you identify a person that’s already in People, Photos offers to merge the two entries into one.
I’m finishing up a new edition of my Photos Crash Course ebook that will cover a whole lot more about Photos on macOS Sierra and iOS 10. When it’s ready to go we’ll announce that here at Six Colors.
By Jason Snell
February 1, 2016 12:49 PM PT
Longtime Mac writer Ted Landau posted this on Twitter earlier today, and since I wrote the book on Photos for Mac, I was able to help him out:
Help! I was unaware “Copy Items to Photos Library” was disabled in Photos. Is there a quick way to now truly import all referenced photos?— Ted Landau (@tedlandau) February 1, 2016
By default, every image you import into Photos from your hard drive is copied into the Photos library. You can throw away the file that’s out on your desktop if you like, because a copy of it now resides inside the Photos library package. But some people want more control over their photos, preferring to organize their image files themselves, in the Finder. For those people, Apple offers a setting in Photos Preferences: “Copy items to the Photos library.” If you uncheck that box, any image you copy into Photos will not be copied into the library package. If you delete the photo later, Photos won’t be able to do anything to bring it back.
Accidentally unchecking that box can lead to some terrible consequences—like you deleting your photos without realizing you have no backup! Fortunately, in Ted’s case the photos still existed—but he had moved them to an external volume. Ted’s question then, was twofold: Can he do something so that those images are entirely copied into his Photos library, and what happens if he’s moved the image files in the meantime?
First off, it’s worth noting that Photos displays a special icon on any photo that hasn’t been copied into its library: In the bottom-left corner of a thumbnail, it will display an image of a square with an arrow. (If it can’t find the source image, this becomes a yellow alert symbol with an arrow.) You can toggle this icon on and off via the View: Metadata: Referenced File command.)
Fortunately for Ted, Photos does include a command that will find all the source image files and copy them into the library. To perform this task, open Photos and select the photos you’d like the app to copy, then choose File: Consolidate. If you haven’t moved the files anywhere, once this task is completed your Photos library will be whole again.
Ted moved his items to a different hard drive, but if Photos can’t find a certain photo in its original location, it will ask you to pick a folder to search in. Ted was able to point Photos at his alternate disk, and then the app was able to import all of those files.
So if you ever regret leaving items outside of your Photos library, you can import them later with the Consolidate command. But for most people, it’s a better idea to leave the “Copy items to the Photos library” preference checked, now and forever.
[If you want more tips about Photos, check out my book, Photos for Mac: A Take Control Crash Course.]
By Jason Snell
December 1, 2015 9:05 AM PT
One of the more interesting features of Photos for Mac is its ability to not store my entire photo library on my Mac’s drive.1 It does this by syncing the entire library to iCloud Photo Library2 and then dynamically loading and unloading photos as you use it.
In true Apple fashion, Photos protects the user from thinking about managing storage — everything happens automatically, with absolutely no intervention from the user. That’s as it should be, but a few optional controls for the control freaks among us wouldn’t be the worst thing in the world.
This thought occurred to me when I was fishing a file out of my Pictures folder and noticed that my Photos library takes up 46GB of my precious iMac SSD storage space.
That’s a lot, especially when you’re supposed to render an HD video in Final Cut Pro, but you can’t because you’re out of disk space. There’s no button for me to press to put Photos in Austerity Mode, no interface to force it to slim down what it’s using. In fact, there’s no communication at all from the app about how it manages its own storage space.
Plumbing the depths of the Internet, I found this pretty great post on StackExchange that charts the size of the Photos library and a Mac’s disk usage. Photos is definitely optimizing the size of its library, though it’s still not entirely clear to me whether it only does this when it’s running, or if there’s some background process that might do it all the time. (My guess is that it’s the former.)
What that post does clarify is that Photos apparently has an optimization target: 10 percent of free disk space. So on my 467GB partition, it’s trying to free up roughly 47GB of free space. (At the moment that drive has 42GB free, so I guess it’s working?)
I’m also a little surprised at the 16GB of thumbnails in my Photos Library. That’s 240K in thumbnail data for every one of my 67,782 photos. It turns out that the Photos library actually generates two thumbnail files for each image: one “1024” image (roughly in the ballpark of 1024-by-768 pixels, though it varies based on aspect ratio) that’s 200K-300K, and a standard thumbnail that’s more like 480-by-360 and 50K-75K.
Those thumbnails are what make the Photos interface so pretty and responsive, even at Retina resolutions. At the same time… 135,000 thumbnail files on my SSD taking up 16GB of space. I guess that’s the trade-off of having a huge cloud photo library, but… wow.
I’m so happy that this feature exists, but in a future update I’d love to see a bit more transparency about how the storage is being optimized, and perhaps even a user option to blow out the cache or reduce the library size by some amount. Or, failing that, it needs to be much more aggressive in pruning its library in low-disk situations.
By Jason Snell
November 6, 2015 11:22 AM PT
Because I wrote a book about Photos for Mac, a user group in Chicago asked me to give them a presentation about Photos, which I did earlier this week.1 At the end of the presentation, someone asked about merging the contents of multiple Libraries together, and I had to give them the bad news: There’s just no way to do it.
Less than two hours later, there was an email in my inbox from Fat Cat Software, makers of the go-to utility for merging iPhoto libraries (as well as a bunch of other iPhoto-related stuff), iPhoto Library Manager. Fat Cat has a similar utility for Photos, PowerPhotos, but due to the limitations of the Photos app itself, it wasn’t able to merge libraries together.
It turns out that a lot of those limitations of Photos were erased with version 1.1, released with OS X El Capitan. Now PowerPhotos has been updated to version 1.1, and it has added support for merging multiple Photos libraries together into one. (It’s got a bunch of other useful features, including the ability to detect and remove duplicates and to view the contents of a library as a list.)
There are some limitations, however. The merge feature can bring in the edited version of your photo, or the original, but not both; and manually assigned locations, faces, and projects aren’t supported. Still, it’s progress. And Fat Cat has simplified the connection between PowerPhotos and iPhoto Library Manager—a single $30 license works with both apps. (Users of iPhoto Library Manager 3 can upgrade for $15.)
Despite the limitations of this new approach, it’s good to know that there’s finally a way to merge the contents of two libraries together, short of dragging all the images into the Finder, changing libraries, and then dragging them back in.
Now you know, Chicago.
Alas, via Skype, meaning that I was not able to partake of the city’s hot dogs or deep-dish pizza. ↩
By Jason Snell
September 30, 2015 6:12 PM PT
Available now as a part of El Capitan is Photos 1.1, the first major update to Photos for Mac, the replacement for iPhoto and Aperture that Apple launched earlier this year.
Here are the major additions in Photos 1.1:
Geotagging. In Photos 1.1 you can add a location to an image or batch of images that weren’t geotagged, as well as edit the location of data of already-geotagged images. To do this, you open the Inspector window by pressing Command-I. In a not-yet-geotagged image, the Inspector will display a line labeled Assign a Location. Clicking in this area will let you enter a street address or a name of a point of interest, and Photos will search Apple’s Maps database. If that location isn’t good enough for you, you can always click on the pin and drag it around the map, placing it wherever you like.
For photos that have already been geotagged, you can click on the location label above the map in order to search for a new location, or just click on the pin and drag it to a new location. This behavior works whether you’ve got one item selected, or many. There’s also a new menu item that lets you remove location data or revert to the location data of the original photo.
If you’re using iCloud Photo Library, you should know that changing the geodata on the photos will sync, so you’ll be able to see the new locations on iOS devices and other Macs. In fact, Macs running Yosemite will still see the geotagging data, because although Photos 1.0 doesn’t let you edit geotagging data, it does let you view it.
Batch titling/describing/keywording. If you want to name a whole bunch of images in one go, or add a description, or add keywords, you can do all of those things, too. Just select a bunch of images and, again from the Inspector window, click in the Add a Title, Add a Description, and Add a Keyword fields and add what you need to do. (Sadly, there isn’t a way to apply something like a unique serial number (i.e., Photo 1 followed by Photo 2) in a batch.)
Album sorting. In the first release of Photos, albums could be sorted in one way: by date, with the oldest on top. In Photos 1.1, you can now sort photo albums by date with either the oldest or newest on top, or alternatively you can sort the photos by title. You can also still keep freestyling it, and drag the images into any order you want. You can also sort your list of photo albums by name, or by date (newest or oldest first), if you feel your albums themselves need some organizing.
Editing extensions. Photos now supports image-editing extensions written by third-party developers. Like the built-in editing tools, you can actually stack multiple extensions while editing a photo, so you can combine third-party editing extensions with Apple’s own tools to get exactly the image that you want to see. However, each extension edits a “burned-in” version of your photo, so you can’t edit a photo with three extensions and then go back and turn off the first of the extensions. Instead, you’d need to revert back to the original photo (which is always retained by Photos) and start again.
Editing extensions will be available from the Mac App store, either bundled with an existing app or distributed as standalone extensions. I’ve tried a few beta versions of photo-editing extensions, and they definitely add a new dimension to what you can do without leaving Photos.
Other stuff. The Recently Deleted folder is now visible all the time, not just when you enable it from a menu item. There’s a new Reduce Motion checkbox in the Preferences window that claims it reduces the motion of the user interface, though I haven’t picked up on quite what it’s reducing.
There’s support for the Live Photo feature introduced with the iPhone 6S and 6S Plus. Hovering your cursor over a live photo for a fraction of a second will start the photo playing; you can turn this off with the Turn Off Live Photo command under the Image menu. In the larger photo view, there’s a Live Photo sticker you can click on to start playing the Live Photo.
[Want to learn more about Photos for Mac? Buy my book, “Photos for Mac: A Take Control Crash Course”. And yes, it will be updated in the next month or so to reflect all the changes in Photos 1.1.]
By Jason Snell
July 9, 2015 11:44 AM PT
Due as a part of El Capitan this fall, and available right now as a public beta is the first major update to Photos for Mac, the replacement for iPhoto and Aperture that Apple launched earlier this year.
Here are the major additions you can expect to see in Photos when 1.1 arrives this fall (or when you install the public beta, depending on your enthusiasm):
Geotagging. Yes, in Photos 1.1 you can add a location to an image or batch of images that weren’t geotagged, as well as edit the location of data of already-geotagged images. To do this, you open the Inspector window. A not-yet-geotagged image will offer a section of the window labeled Assign a Location. Clicking in this area will let you enter a street address or a name of a point of interest, and Photos will search Apple’s Maps database. If that location isn’t good enough for you, you can always click on the pin and drag it around the map, placing it wherever you like.
For photos that have already been geotagged, you can click on the location label above the map in order to search for a new location, or just click on the pin and drag it to a new location. This behavior works whether you’ve got one item selected, or many.
Batch titling. If you want to name a whole bunch of images in one go, you can do that, too. Just select a bunch of images and, again from the Inspector window, click in the Add a Title field and add your title. (There doesn’t appear to be a way to apply something like a unique serial number (i.e., Photo 1 followed by Photo 2) in a batch.)
Album sorting. In the first release of Photos, albums could be sorted in one way: by date, with the oldest on top. In the Photos 1.1 public beta, you can now sort photo albums by date with either the oldest or newest on top, or alternatively you can sort the photos by title. Apple says other sorting options may arrive before Photos 1.1 ships, but I’m not sure what they might be.
Editing extensions. Photos will support image-editing extensions written by third-party developers. Like the built-in editing tools, you can actually stack multiple extensions while editing a photo, so you can combine third-party editing extensions with Apple’s own tools to get exactly the image that you want to see.
Apple says editing extensions will be available from the Mac App store, either bundled with an existing app or distributed as standalone extensions. I haven’t had a chance to try any editing extensions out, unfortunately, so I can’t report more about this feature yet.
Other stuff. Apple says you’ll be able to batch organize Faces, letting you drag multiple photos onto a Face to assign them to that person, but I couldn’t make that work in this beta. Apple also says that large libraries can launch up to 40 percent faster than in Photos 1.0, something I won’t be able to verify until I upgrade one of my primary photo libraries to the public beta.
[Want to learn more about Photos for Mac? Buy my book, “Photos for Mac: A Take Control Crash Course”. And yes, I plan on updating it when Photos 1.1 gets closer to shipping.]
By Jason Snell
April 10, 2015 12:09 PM PT
I’ve been using Photos for Mac since day one of its beta release—have I mentioned lately that you should buy my book about it?—and on day one I encountered a problem that, surprisingly, seems to have gone unfixed throughout the entire beta process.
The first day I used Photos, I imported a substantial portion of my family photo collection—20,000 or so photos—into what Photos calls the System Photo Library. And set it to upload to iCloud.
The next day, my Internet connection seemed to die, or at least become sporadically inert. Traffic would sometimes squirt through, but after long delays. It was weird, and intermittent, and I was really sad.
Later that day I discovered something, though: Even though Photos wasn’t open, a background task was uploading my photo library to iCloud. All 20,000 photos. The process was using all the available bandwidth, saturating my outbound Internet connection and making it essentially unusable. (Was Comcast also throttling me due to a sudden explosion of uploading data? I don’t know, but the net result was the same. And the moment I paused the upload, all the problems went away.)
If you’re trying out Photos and wondering why your Internet is suddenly slow, now you know! Fortunately, Apple provides you with a way to pause the upload—a single button labeled “Pause for one day.” (Note that Photos needs to be using the System Photo Library for you to see this option, because that’s the only library that syncs with iCloud.)
This is certainly better than a boot to the head, but it’s not enough.
What Apple needs to do to fix how Photos syncs with iCloud is take a tip from online backup services like CrashPlan and Backblaze. Yes, it’s good to upload things fast, especially when you’re doing your first backup. But these services combine some intelligence with user settings to not make the Internet unusable while they operate.
Perhaps photos could sense when someone’s using the computer and throttle back the upload speed. Or let users optionally choose hours when uploads should take place, and when they should be curtailed. Or let users choose how much bandwidth the backup can use. (Or, if you want to be all Appley about it, Photos could figure out how fast a user’s connection is and try to use a conscientious percentage of that bandwidth.)
Users with bandwidth caps should be able to somehow throttle the uploads so they don’t end up with bandwidth overages. And users should be able to pause iCloud uploads indefinitely, not just for one day. Bug me if I’m still paused after a few days, sure, but don’t force me to open Photos every day and pause the upload just so I can visit websites or make a Skype call. Pauses for shorter amounts of time—just this next hour when I’m FaceTiming—would also be welcome.
I understand that Apple doesn’t want to junk up the Photos interface. A commitment to simplicity is admirable. But in this case, what’s there is not enough. If Apple wants to commit to that simplicity, it can make this feature as hands-off and intelligent as it likes. Or it can punt and provide users with nerdy settings to control all of it like the online backup services do. Maybe it could even pick some nice middle ground between those two extremes.
What it shouldn’t do is abdicate all responsibility for what the initial iCloud photo backup does to an Internet connection. In version 1.0 of Photos, that’s what it feels like Apple has done. I don’t think it’s good enough.
By Jason Snell
April 8, 2015 2:22 PM PT
With the release of OS X 10.10.3 today, Photos for Mac is available to the general public. I’ve been using it from the first day it was released as a developer beta because I’m writing an ebook about it. And so I’ve learned a lot about it.
If you’re used to iPhoto, Photos won’t be that jarring. Photos can import your iPhoto library and retains most, but not all, of the features of iPhoto. Star ratings have been demoted to keyword status, flagged items are now Favorites, and Events are now just another kind of photo album. But with the optional sidebar displayed in Photos, you’d think you were using a slick new version of iPhoto.
Hard-core Aperture users will probably be disappointed. Photos is much more iPhoto than Aperture. If you use Aperture because it’s more than iPhoto, but haven’t availed yourself of most of Aperture’s features, you may find Photos sufficient. But if you rely on one of the many Aperture features Photos doesn’t support, be prepared for disappointment.
You should read my Photos FAQ, which I wrote back in February and just updated.
If you’re wondering about how importing libraries from iPhoto and Aperture works, check out my story about how Photos accomplishes that task.
By Jason Snell
April 6, 2015 10:20 AM PT
I’m writing a book for TidBITS/Take Control about Apple’s new Photos app, which is due out with OS X 10.10.3. This app is the replacement for both iPhoto and Aperture.
The book costs $10 and we’re now taking pre-orders. If you buy it now you’ll actually receive the first half of the book! The second half will be available soon after Photos arrives in its final form, and all buyers will get upgraded to the full book when that happens.
The book is a visual guide to the new Photos app. The PDF edition is quite attractive, if you ask me. If you’re interested in this new Photos app, I encourage you to check it out.
By Jason Snell
February 11, 2015 4:01 PM PT
[This story was updated on April 8, 2015. If you want to know more about Photos for Mac, you should pre-order my ebook. If you order it now you’ll get the first half of the book immediately, even as I’m writing the second half!]
After my Photos for Mac overview appeared on TidBITS, I’ve been pelted with questions about Apple’s forthcoming replacement for iPhoto and Aperture. Presented here, then, are quick answers to simplified questions about Photos for Mac.
I keep my existing iPhoto/Aperture library on an external drive. Will the program continue to use that location automatically?
Yes. Photos automatically detects if you’ve got an iPhoto or Aperture library and if you have only one on your system, it’ll use it as the basis for its new library without duplicating the media. If you’ve got more than one library, it’ll ask you which one you want to convert and set as the system library.
What happens to my old library?
It’s still there. The next time you try to open it, iPhoto or Aperture will remind you that it’s been migrated to Photos, but that’s just a reminder—you can keep using iPhoto as usual if you want. However, changes you make in libraries after they’re imported do not sync to the other app. You can’t import an iPhoto library to Photos, then edit something in iPhoto and expect to see it also edited in Photos. It doesn’t work that way.
What if I want to convert my library and save it in a different location?
Library conversions always happen in the same folder, for the very reason you specify. If you want to move the library later, that’s fine—if it moves to a different volume, that data will copy and the hard links will be disassociated. It’ll just be a regular library.
Can I have more than one Library?
Yes. Hold down option when launching Photos to pick a library or create a new one. Only one library can be designated as the System Photo Library. That’s the one that syncs with iCloud.
Can I organize my photos myself, in folders on my hard drive, and still use Photos?
Yes. There’s a “Copy items to the Photos library” setting in the General preferences tab. If you uncheck it, then Photos will consider the canonical version of that photo to be the file you dragged in. (This is signified by a small alias icon in the lower left corner of the image.) If you delete that photo later, Photos will no longer have access to the full-resolution image. However, referenced media files don’t sync to iCloud.
Will Photos support extensions to expand its capabilities?
Apple suggested at much when it announced Photos, but beyond support for sharing extensions there are no signs of addition extensions in 1.0.
Is Photos a direct replacement for iPhoto?
Yes. It’s basically iPhoto X — a reworked iPhoto that drops some iPhoto features but will feel quite familiar to iPhoto users.
Is Photos a direct replacement for Aperture?
No. It’s a step back from Aperture, and people who use Aperture to the fullest will probably be frustrated by this version’s limitations. People who didn’t take advantage of most of Aperture’s features might like it, though.
How does the new iPhoto handle burst mode pictures? Does it auto stack/group them?
iPhone burst mode photos come in as stacks. If you take 50 photos in a very short amount of time with an SLR, though, those seem to just come through as a whole bunch of individual pictures.
I don’t want to use iCloud with my photos. What do I do?
Just keep iCloud syncing turned off. That’s it. iCloud syncing is optional, not required.
I gave up and moved my library to Dropbox along with all my photos. Is there any reason to move back to iCloud?
The big advantage of Photos is that you don’t need to have your entire photo library anywhere except in iCloud. My iMac’s hard drive isn’t big enough to hold my iPhoto library, so I can’t sync it with Dropbox on this iMac. But I could open that same library in Photos, because almost none of the images would need to be stored locally.
If you’re someone who wants all your photos on your hard drive at all times, you could do that with Dropbox and Photos rather than iCloud.
Is sync to iCloud ‘all or nothing’? What I want is the ability to choose which photos sync from the Mac.
You can sync everything in the system Photos library, or nothing. That’s it.
iPhoto’s still on my Mac. Can I delete it?
Sure, if you want. Apple keeps it there just in case you want to get your iPhoto libraries in order before importing them. There’s no harm in keeping it around for a little while, but you can delete it if you need to. Keep in mind that deleting imported iPhoto libraries probably won’t save you much space.
Can I still sync photos to my iOS devices via iTunes?
Yep. It works just as you’d expect—choose Photos as the app you’d like to sync from, then you can sync everything, just certain albums, only favorites, or even all the photos from a recent period like the last week or last month.
By Jason Snell
February 10, 2015 12:27 PM PT
[Updated April 9 to account for the final release of Photos for Mac. Also don’t miss our Photos FAQ.]
As I wrote my TidBITS article about the initial beta release of Photos for OS X, I was struck by how iPhoto imports work, which I described like this:
The Photos import process is friendly when it comes to disk space — it doesn’t duplicate the photos it imports from iPhoto and Aperture, so you don’t lose precious storage space.
What is this magic? How can it not duplicate the photos, yet not risk losing all your data if you were to throw away your old iPhoto library?
I had an inkling that this was all happening due to a feature of OS X that I believe has previously only been used by Apple in Time Machine, and prodded by TidBITS reader Bryan Walls, I confirmed it this morning. Photos uses Unix-style hard links when importing iPhoto libraries.
Mac users are probably more familiar with the concept of soft links, also known as “symbolic links.” Mac users would recognize the idea of a soft link from the long-time Mac concept of aliases1. In both of these cases, there’s something that looks like a file or folder/directory that’s actually just a reference to the real version of that file somewhere else in the filesystem.
Hard links aren’t like that. The best way to think of a hard link is that the contents of a file appear to exist in more than one location. If a file has two hard links, and you delete one, the file isn’t deleted—because it’s still linked to from another location.
That’s what the iPhoto import inside Photos does2: It creates hard links to the contents of your iPhoto library inside the Photos library. If you delete your iPhoto library, the files that were hard-linked from the Photos library still exist in the Photos library and aren’t deleted. For Mac users used to the a-file-is-a-file approach of the Finder, it’s a bit of a head-scratcher.
Time Machine uses this approach to create full backups while saving disk space. When you delete an old Time Machine backup, any files that are still hard-linked from subsequent backups remain intact. Any files that no longer have hard links elsewhere are deleted. iMovie apparently uses it, too, from time to time.
You can actually see if a file is hard-linked by using the Terminal. Before I imported my iPhoto library, here’s what an image deep inside the iPhoto library package looked like:
jsnell% ls -l total 5968 -rw-r--r--@ 1 jsnell staff 3054588 Jun 10 2013 WWDC13_0910.JPG
1 just before “jsnell staff” lists how many hard links exist to this particular file. One link, the one we’re looking at.
But after I import this iPhoto library into Photos, here’s what that same directory looks like:
jsnell% ls -l total 5968 -rw-r--r--@ 2 jsnell staff 3054588 Jun 10 2013 WWDC13_0910.JPG
Now there are two. To find the location of the two links, I find the unique ID of the file in question:
jsnell% ls -li total 5968 10652722 -rw-r--r--@ 2 jsnell staff 3054588 Jun 10 2013 WWDC13_0910.JPG
And then another Terminal command shows me where those two links are:
jsnell% find /Users/jsnell -inum 10652722 /Users/jsnell/Desktop/An iPhoto Library.migratedphotolibrary/Masters/2015/02/10/20150210-110352/WWDC13_0910.JPG /Users/jsnell/Desktop/An Photos Library.photoslibrary/Masters/2015/02/10/20150210-110352/WWDC13_0910.JPG
This reveals two interesting facts.
When Photos migrates an iPhoto library, it changes the file extension on the iPhoto library package to .migratedphotolibrary.3
On import, Photos makes a hard link to all iPhoto media assets in its own library package, using the same directory structure as iPhoto.
So what happens if you edit one of those files? Something very clever, it turns out: If I open the JPEG image from the migrated iPhoto library in Photoshop, edit it, and save it, that version is indeed altered—but the version in the Photos library is untouched. Basically, modifying that file causes the link between the two versions to break. They’re different, and no longer connected.
I can also confirm that Photos is pretty comprehensive when it comes to its iPhoto import. Both Albums and Smart Albums are imported, and the Smart Albums remain “smart.” Smart Albums based on deprecated data like star ratings still work—since star ratings are converted to keywords, Smart Albums based on star ratings are converted to search for the equivalent star keywords. Descriptions, titles, flags, and geotagging from iPhoto are all picked up as well, and iPhoto Events are imported as Albums.
If you’ve edited a photo in iPhoto before importing, Photos will display that edited version—but the original has also imported behind the scenes, so you can revert back to it if you need to.
Pedantic note: OS X aliases are not the same as unix symbolic links. But in general terms they do more or less the same thing: connect a “real” file to a separate representation of it. ↩
It doesn’t seem to do this when you just drag images into Photos—in that case, it copies a version of the photo into its own Photos Library package. ↩
It also uses the iPhoto library’s name as the basis for the imported Photos library’s name, which is why my “An iPhoto Library” was imported as the amusingly wrong “An Photos Library.” ↩