Aperture is Updating Previews

by Josh Anon

Aperture 1.5 added a new preview feature, and since I've received a few questions about it lately, this week's blog will be devoted to discussing how Aperture uses previews. If you're like me, you've noticed that periodically, especially right after importing your images, you will see "Generating Previews" listed in the task window. Plus, sometimes when you try to quit Aperture, an alert will pop-up saying that Aperture is generating previews. Unfortunately, there's no little box in Aperture that says what Previews are useful for!

It's a common misconception that when you click on an image, while waiting for Aperture to decode the RAW file, you're seeing the preview in the viewer. This actually isn't the case (to the best of my knowledge); instead, you're seeing a large thumbnail. However, if the RAW file isn't available but a preview is (and the preview is larger than the large thumbnail), Aperture will display the preview instead of the RAW file. In other words, when using offline images, Aperture will generally use previews.

Now the question is at what other times will Aperture use your previews?

  • When you drag and drop the image thumbnail to another application, Aperture will put the preview on the pasteboard.
  • If you use slide shows and have them set to not load the RAW files, Aperture will use previews.
  • If you use your Aperture images in iLife applications, like iDVD, those applications will use your Aperture previews.

If it turns out that you don't ever need previews, you can save some hard drive space and processor time by deleting your previews and turning preview generation off. To do so, follow these instructions:

  1. Click on the Action menu (gear icon) above the Library and uncheck "Maintain Previews for All Projects"
  2. Control-click on the Library and choose "Delete Previews for Library"
  3. Under Preferences, uncheck "New projects automatically generate previews" to stop new previews from being automatically generated

If previews really are useful for your workflow, make sure that you are using them efficiently--limit their size and resolution! Under Preferences, there is a slider for the image quality. Somewhere between 5 and 8 should be sufficient, depending on if you'll want higher-quality images or not. Under the Limit Preview Size popup, if you have it set to "Don't Limit," then Aperture will create previews at the same size as the original image. You will be fine limiting the preview size to the size of the largest screen you'll be working on, such as 1440 x 1440 for a 15" MacBook Pro.

Sometimes, you'll notice that a preview is corrupt or out of date. When this happens to me, I first control-click on the image and choose "Update Preview." If that fails to do the trick, I'll hold down Option and then control-click on the image and choose "Generate Preview." If that still doesn't work, I'll control-click, pick "Delete Preview" and then option-control-click and choose "Generate Preview." I have yet to find a bad preview that those steps won't fix!

Last but not least, if you're really unhappy with when Aperture generates previews, either uncheck the "Maintain Previews for All Projects" under the Project Panel's Action menu or control-click a specific project and uncheck "Maintain Previews for Project." Now, you have full control over when Aperture will generate previews (select the images, option-control-click, and choose "Generate Previews").

One final note on a different topic--I will be speaking at the Cocoaheads meeting this Thursday about Aperture plug-ins at Apple in Cupertino. Feel free to attend!


2007-05-09 09:41:43

At the risk of asking the obvious, what is a "bad" preview? I've been using Aperture since 1.0. To my knowledge, I have not seen a bad preview. Thanks.

Josh Anon
2007-05-09 09:49:06
Good question! Sometimes, Aperture might have a problem reading the RAW file and turning it into a preview--there will be gray pixels or just garbage in the preview. Another example is if you make a change, especially in an external editor, and Aperture doesn't update the preview right. That would be a bad preview since it's out of date.
2007-05-09 10:17:17
I shoot mostly JPEGs. I find it handy to be able to drag and drop images between applications. In these circumstances, employing previews is sort of a waste, because they duplicate disk space for little benefit (the source JPEGs are fine). Unfortunately, without previews generated, Aperture is dumb and mute when one tries to drag an image to another application. Is there some way around this?
Josh Anon
2007-05-09 10:28:27
Off the top of my head, I don't know if you can make Aperture support dragging JPEG master files. That seems like a reasonable sug, though! Send it in at http://www.apple.com/feedback/aperture.html
2007-05-09 13:30:52
Silly question - how do you make Aperture use RAW files for slideshows? Everytime I click slideshow, I get generating previews...
2007-05-09 13:34:14
Ah found it - set image quality to good instead of best... Doesn't really make sense to me.
Wolf vW.
2007-05-21 13:19:36
Hi - you talk about the JPEG export to iLife applications. I noticed a few times now that when I create an album in aperture with photos I want to export e.g. into iWeb, they do NOT show up in the same order in the media tab in iWeb. What drives the sorting in iWeb (or other iLife apps for that matter) and how can I influence it not to resort the images in iLife?? Appreciate any hint! Thanks.
Arturo Guerra
2007-05-26 17:04:00
Hi - I was hoping to reduce the size of my library when relocating masters to DVD. Here are some numbers I got: Library Size with masters: 100%, after relocating masters: 39%, after deleting previews: 30%. Is there some way of reducing that 30% even more ?
Thank you.

2007-05-27 08:25:52
Wolf vW, off the top of my head, I'm not sure. Perhaps it's date-driven sorting? I would suggest playing around and seeing what you can find.

Arturo, probably not. Aperture always tries to keep some information around for each image, including thumbnail files. If you delete that information, it'll be automatically regenerated. However, if your camera was set to shoot RAW+JPEG, you could delete the master JPEG files (so that you only have the master RAW files) to save space.