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:
- Click on the Action menu (gear icon) above the Library and uncheck “Maintain Previews for All Projects”
- Control-click on the Library and choose “Delete Previews for Library”
- 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!