One of Aperture’s more curiously powerful features is Stacks. Unfortunately to the uninitiated, it’s probably just as confusing as it is useful—a point apparently recognized by Apple itself; when Aperture 3 was released, they set the default position of the “Automatically stack new versions” preference to off.

Right then… What are Stacks?

Stacks are a collapsible collection of photos. There are two primary uses for stacks:

1. To collect a series of similar images where you only want one to be prominent. These are usually shot in a sequence, for example the series of shots leading up to the wedding kiss, the series of shots leading to the touchdown, the series of nearly identical shots of a flower. In editing, the idea is that you’d “pick” the best shot, and that would go to the top of the stack. Close the stack, and you only see the best one. Open it, and you see the rest.
2. To manage a series of Versions of the same image. If you have a photo and create a series of versions (say a B&W one, a cropped one, or just a series of experiments of adjustments), then they can all be kept together in a Stack so you know at a glance that they are in fact the same photo. Ultimately you “pick” the one you like best, and again when you close the stack, you only see the favorite one.

There is no visual differentiation between these two uses, which may be to blame for some of the confusion. And there’s nothing stopping you from combining these two uses either; ten photos in a sequence, plus a handful of versions of those photos, can all be in a single stack.

Then just to add another level of complexity, you have two stack designators; the Stack Pick and the Album Pick. This allows you to have a different pick in an Album than in the Project. You don’t have to, but you can. Confusing, yes, but also dead useful.

So with all that on the table, let’s go through the steps.

Making a Stack

The first step is of course to make a stack. There are several ways to do this.

Auto-stack; on import or anytime

Aperture has always featured the “auto-stack” tool. It used to be a slider in the Import dialog, as that was meant to be the most common time to use it. It also was (and still is) available as tool in the menubar. It’s no longer built-into the Import dialog interface, but you can still call it up there if you want.

Selecting the menu Stacks > Auto-Stack brings up the Auto-Stack Images HUD (Heads Up Display). This has a single slider on it, that goes from 0:01 (seconds) to 1:00. As you slide this, images that are in view start jumping together based on the time between shots. So if you are stacking a sports game, where you were shooting rapid fire sequences at several frames per second, just going to the first step of 0:01 seconds will cause those shots to jump together into a Stack. Or, if you were shooting something slower moving, like a flower that you were capturing from a variety of angles, you can drag the time slider up as high as one minute between frames.

This is mostly useful for the rapid-fire sequences, because any burst will jump together, and as long as there was more than a single second between bursts, those sequences would separate and stack into their own groups. Auto-stacking sequences that have more time between them is more likely to end up with stragglers or even photos that end up in the wrong stack. Fortunately that’s easy to fix (we’ll get to that).

Manual stacking

You can also make selections of images and stack them with a single command. I personally find this a more useful and reliable way to stack; for me, the auto-stack rarely gets the groups right. But then again, I don’t often shoot sports so my collections are more likely to be spread out over a variety of times between shots.

To manually stack a collection, first select the images in the Thumbnail view (keep in mind they do not have to be sequential; any collection of images, regardless of when they were shot, can be stacked), then choose the command Stacks > Stack. The keyboard shortcut for this is Command-K — definitely a useful one to remember if you’re going to do this often.

In the screenshot above, notice that the two red flower shots are selected, so when the Stack command is invoked, they will stack together.

Anatomy of a Stack

Stacks are easily identifiable by two things. First, the background behind an open stack of images is a darker grey than that of non-stacked images. Second, all stacks (open or closed) will have a number and a Stack icon on the first thumbnail indicating how many images are in that stack.

In the screenshot above, you can see that three very similar images have been placed in a Stack. We know there are three because of the little 3 on the Stack icon. The images on either side are not in that Stack, nor are they in any Stack.

To close (or open) the Stack, just click on the number icon.

Above you see that same stack, now closed. It still shows the 3, telling me there are three images total in that Stack.

Changing a Stack

Once a stack is created, you can change it all you want. You can split stacks, extract items that don’t belong, and even combine stacks.

Notice the two commands highlighted in the screenshot above; Split Stack and Extract Item. Also notice that this stack has four photos in it (see the 4 icon, and of course you can see four photos), and notice that the first seed-pod photo is selected. At this point, if you chose Split Stack, then that seed-pod photo would become the first image in a new stack of 2, and the two red flowers would be left in their own stack of 2.

If instead you chose Extract Item, then that single seed-pod photo would be extracted from the Stack, leaving the other 3 behind. You can also just drag a single or multiple photo(s) out of a stack to remove it/them.

You also have the Unstack option, which simply unstacks all images in the selected Stack, putting things back to “normal”.

To combine Stacks, just select any number of them (you don’t have to select the entire Stack; any image in it will do fine) and choose the Stack command again (Command-K).

Promoting and Demoting

A stack doesn’t have to be just about the Stack Pick — it can also be about sorting the photos in order of favorites. Again that’s up to you, but as you look through the sequence, you can promote or demote photos in the stack as you see fit.

You can see in the screenshot under “Changing a Stack” that there are commands Promote and Demote, with keyboard shortcuts Command-[ and Command-], respectively. Again if you’re going to get serious about this, definitely remember those shortcuts.

As you promote or demote an image, this is what you see (you should see an animation below; if you don’t, try double-clicking on it, or right-click on it and open it full screen. Chrome was being persnickety about this in testing):

You can move the image all the way to the top, making it the Pick.

Selecting a Stack Pick

As just mentioned, you can promote an image all the way to the top of the stack, making it the Stack Pick. Or, if you know exactly which image you want to put to the top, you can simply select it and mark it as the Pick from the menu Stacks > Pick or the keyboard shortcut Command-\.

NOTE FOR LION and 1PASSWORD USERS: The shortcut Command-\ seems to not work in Lion with 1Password installed. I’ve tested it on two systems, and if I force quit the 1PasswordAgent, then even after it starts back up, the shortcut works. But until it’s force-quit, it doesn’t. I’ll report this to AgileBits and see what they say. The best solution would be to assign a new keyboard shortcut to the command in the Commands editor (menu Aperture > Commands > Customize…) because if you’re like me, living without 1Password is NOT an option!

Remember, when you close the Stack, whatever is on top (i.e. the first image) is the only one that’s shown. Hence, the “Stack Pick”.

So What’s an Album Pick?

This is more likely going to be useful if you’re using the Stack to hold different versions of the same photo, such as cropped, B&W, different colors, etc. (I’ll show you how to automatically stack new versions later).

Let’s assume now that you have a Stack with a handful of different variations of a photo, like this:

The current Stack Pick is the aged image with the white border. Cool.

But let’s say you want to make an album of B&W images from this shoot. Instead of extracting that B&W version from the Stack, you can use the Album Pick option, which defines a Pick but only for that Album!

First, drag the stack into the B&W Album (it doesn’t matter what you grab when you drag in a Stack; the entire Stack will go, always). Then switch to the B&W Album and select the B&W photo, and finally choose the command Stacks > Set Album Pick. The photo won’t move as it does when you assign a Stack Pick, but instead, it’ll get a little check-mark in a circle, like this:

Now when you close the Stack, that B&W image will be on top, as if it were the Stack Pick—except of course that it’s only the Pick in this Album.

I use this often when delivering different versions of the same image to different clients; i.e. a magazine needs a specific crop, but that’s now how I published it on my website, etc.

You can clear the Album Pick from the same place; once it’s been set as an Album Pick, if you select the image and go back to the menu, you’ll see it’s changed to Clear Album Pick:

If you clear the Album Pick, then the Stack Pick goes back to being the Pick for that Album.

Enabling “Automatically stack new versions” in Preferences

If you are new to Aperture since version 3, chances are you’ve never even seen Stacks, since as mentioned in the beginning, automatically stacking new versions has been turned off by default. To turn it on, just go to the menu Aperture > Preferences… > General and enable “Automatically stack new versions”:

Now whenever you create a new version, either manually or because you opened a photo in an external editor and it created a new version for you, it will be stacked. And remember if you want to go back and stack some previous sets, all you have to do is select them and tap Command-K.

Making a Stack with a Predetermined Stack Pick (sometimes)

This is a tip that I’ve noticed doesn’t work all the time, unfortunately. And for the life of me I can’t figure out the pattern—if you do, please let me know in the comments and I will update this article.

If you’re selecting a pile of images to put in a Stack, and you already know which one you’re going to make the Stack Pick, it makes sense that you should be able to select and stack them in a way that the Pick is set for you. When you select a range of images, there’s always a Primary Selection; that’s the one with the heavier white border around it, like this:

See how the middle image has a heavier white border? That’s the “primary selection”. Now, if you hit the keyboard shortcut Command-K to make a new stack, about half of the time, that image will automatically be promoted to Stack Pick. And the other half of the time, the Stack Pick will just be the first image in the selection.

Bizarre… so if you figure it out, let me know. I usually do it and hope, and if it doesn’t mark it, then I just manually select and hit the Pick shortcut. Still saves time, but it’s just weird.

What does seem to always work is whichever image you select first will be the Stack Pick, if you click, then command-click, command-click on the rest of the images you want to stack. If you just click-drag over them, then the first photo in the selection (not the first image you dragged over) will be the Pick.

Publishing Stacks to Flickr, Facebook, and MobileMe

When you add a Stack to a Flickr, Facebook or MobileMe album, only the Stack Pick will be uploaded. This also means that if you want a different version than the Stack Pick to be published, you can use the Album Pick feature to deterimine which photo is uploaded. Aperture treats all those Flickr, etc. collections as Albums, so the Album Pick feature works there, too.

If you’ve already uploaded a version, and want to replace it with a new version, just assign a different version in the Stack to be the Album Pick, and when you refresh the published Album (click the little broadcast icon to trigger a refresh, or just wait until your next scheduled refresh), that image will be uploaded and the previous one removed. If you do want both images shared though, then you will need to extract an image from the stack, making two unique files in the Album.

WARNING: (This applies to Flickr for sure, and I think to everything else as well) When you replace an image this way, the published image will be removed, not “replaced”. This means any comments will be deleted, and any external links to the original image, broken—so replace with care!

Customizing the Toolbar to Include Stack Buttons

If you’re like me and don’t use Stacks all that often, it’s easy to forget some of the keyboard shortcuts. But I really don’t like going to the menu, so instead, I’ve created a couple of buttons on the Toolbar for my commonly-forgotten Stack commands.

Just right-click on the Toolbar, and select Customize Toolbar… and you’ll see all the Stack buttons that are available.

*Phew*, that was exhaustive…

What started off as a simple post sure turned into a big one :) Maybe I’m making up for not being on here much lately! Anyway, hopefully that answers all the outstanding questions on Stacks, and if there’s anything I missed, let me know in the comments and I’ll update the post.