One of the truly powerful features of Apple's Aperture product is the way that it handles image files, versioning and workflow. In this post I'll explain how Aperture keeps track of your images and the changes you make to them, and why this method is both very efficient on storage and non-destructive.
Highlighted in yellow on the image above is a "stack" of three images. Actually, it's the original photo as well as two versions of it. In this example I happen to be using a RAW image from a Canon 20D camera, but the exact same principle applies to any image file which you import into Aperture. Highlighted in blue are the various adjustments you can make to an image. There are more choices available than I've displayed here. You can add or remove these controls with one of the pulldown buttons in the upper right corner of that blue highlight. One thing worth pointing out here is that there is a section called "RAW Fine Tuning" that only shows up if you're using a RAW image. Otherwise everything else is the same regardless of the image type.
As you can see, all of the controls are in one place. This makes processing of photos very easy and quick as a matter of workflow. If you're working with a RAW image, Aperture automatically applies the pre-defined RAW profile for your camera. You can make slight adjustments here if necessary, but they're not required. I typically increase sharpness as illustrated in this screenshot, although that doesn't work well for certain subjects. The beauty of this interface is that you can do everything by clicking and dragging on the right without having to use any additional pulldown menus or complex navigation.
You can begin to make changes to your image and Aperture will store those changes independently of the original (Apple calls this the "Master") image file. The changes are actually recorded as XML data that gets interpreted and applied on the fly as you view each version. It is not until you actually export an image that a final raster in the format chosen is created with those changes applied. Thus the beauty of this model is that not only can you always come back and undo or modify your changes, but you can also tell what changes have been made!
There is also a substantial disk space savings this way. As each version of an image requires only a few dozen kilobytes of XML to store the information. So in a typical scenario, you'll have the original image file, in this case a 7 mb RAW file plus less than 50 kb of XML per version. Contrast this to Photoshop which saves your image into a PSD file which keeps growing as you make changes. A PSD file based on such a 7 mb RAW file as here can easily grow to 10 times (yes, 70 mb or more) the size of the original file! And you get to save such a huge PSD file for every version (though you probably wouldn't be creating multiple versions for this reason).
A final note on versions. It is not required to make a separate version of an image before applying edits. Aperture automatically begins to keep track of version info when you start to make edits. Again, the original ("Master") image itself is never modified. However, in practice I prefer to create a new version first, and then begin making edits to it. Since version are really, really cheap (< 50 kb) there is really no second thought required about creating them.
Here's a screen shot of what the menu looks like if you right click on an image:
(view the original 1:1 large image)
I generally use the Option-V key combination to create a new version and edit that. In the example above, I have two versions. In Version 1 (the center one in the stack) I've applied all of the basic adjustments to the photo. In Version 2 (rightmost in the stack) I've applied an additional crop to the photo. Doing it this way was merely a personal workflow preference for me. For I can always undo a crop or even duplicate a cropped version and undo the crop in the new version. Just for clarity, the leftmost image is my unmodified master. I could have applied edits to it directly, but in my workflow I chose not to.
Now, let's have a look at how these version files are actually stored. There are two ways you can import images into Aperture. The first and most common method is that Aperture copies the image into its library. The second is that the image remains wherever you have it in your filesystem and Aperture maintains a reference to it, but all versioning information is still kept in the library. I only use the first method, storing everything in the Aperture Library. This has the additional benefit of being able to back everything up into an Aperture Vault (a copy of your entire library in another place), say on an external hard drive. You can have multiple Vaults and they can be "updated" without need to copy your entire library again. I keep three vaults. One on an internal disk, one on an external disk and a third on an external disk off-site. The two externals get rotated monthly.
Here's a screen shot of Finder showing how a specific image and all of the associated metadata is stored within the Aperture Library.
(view the original 1:1 large image)
Taken one step further, here's a detail view of the size of each file. The original image (in this case the Canon RAW file with a .CR2 extension) is highlighted in blue, and all of the changes are stored as Version files with .apversion extensions. These are highlighted in yellow.
(view the original 1:1 large image)
Finally, here's a screenshot of the first part of one of the .apversion files. Note that all of the changes are kept track of as XML:
(view the original 1:1 large image)
There's a lot more on the Aperture Support page at Apple, as well as this Typical Adjustment Workflow video.
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