Aperture Preview images overview
Aperture allows you to create and use JPEG previews of versions in the library. Previews are JPEG images generated by Aperture that represent the original photo with any applied adjustments. Previews speed up the display of photos in Aperture and also allow you to easily use your photos in other applications.
Aperture is preset to create previews for photos in the library. Previews are built as a background activity after photos are imported. You can set Aperture to create and maintain previews automatically as you add or modify versions, or you can create previews manually whenever you need them. To maintain an efficient use of disk space and adequate display speed, you can control the size of previews, from a preview image that has the full-size dimensions of the original down to a preview image that is 1280 pixels in the longest dimension. You can also control the JPEG compression quality of the previews. If your workflows do not benefit from previews, you can configure Aperture not to create them at all.
You can control the creation and maintenance of preview images for an entire library, as well as on a project-by-project or photo-by-photo basis.
When a version has a preview built for it, you can drag the photos directly from the Browser to any application that accepts JPEG files, including the Finder, Mail, and most other applications. If you are dragging multiple photos, but only some of them have previews, only the versions with previews are dragged out.
You can use previews to distribute your Aperture photos in movies, on the web, on DVDs, in slideshows, and in podcasts. You can also download your Aperture photos to devices such as iPod, import your Aperture photos into iPhoto, or use them to create Pages documents. The Media Browsers in the iLife and iWork applications support browsing Aperture libraries. If a version has no preview, the photo is not made available to the Media Browser.
Note: When photos are within stacks, only stack picks and album picks are shared. If you want iLife to have access to a photo in a stack and it’s not the pick, you need to extract it from the stack or make it the pick.
Like photos in iPhoto libraries, photos in Aperture libraries can be used for your screen saver, desktop picture, and Mail, through the same mechanism the Media Browser uses.