Working with Preview Images

Aperture allows you to create and use JPEG previews of versions in the library. Preview images improve the display of images in Aperture and allow you to easily use your images in other applications. These preview images are used to speed up the display of images in the Viewer, in the Browser, and in Full Screen view. Previews are JPEG images generated by Aperture that represent the original master with any applied adjustments.

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 master 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.

Previews are shared with applications in iLife and iWork, and Aperture uses JPEG previews to display images in slideshows. The result is smoother, more responsive slideshows. However, if the previews are absent or not up to date, Aperture must render the preview images before the slideshow begins.

You can control the creation and maintenance of preview images for an entire library, as well as on a project-by-project or image-by-image basis.

Aperture is preset to create previews for images in the library. Previews are built as a background activity after images are imported. If you import a large number of images, it may take an extended time to build these previews. In that case, you may want to temporarily stop the building of previews using the Activity window and then resume building the previews later. Or, you can deselect the “Create previews for existing images” checkbox and build previews on a project-by-project basis, as described in Sample Workflows for Using Previews Effectively.

For more information about the Activity window, see Viewing Preview Generation Progress in the Activity Window.

How Aperture Displays Images in the Viewer

When a version needs to be displayed in the Viewer, Aperture does the following:

  • Aperture draws the thumbnail image (a JPEG image that is 1280 pixels in the longest dimension).

  • Aperture draws the JPEG preview, if present.

  • Aperture decodes the master and applies any adjustments to it.

Once the last step is completed, the adjustment controls become available. Because the JPEG preview is created with all the adjustments for that version, it appears onscreen faster than the adjusted master would. The result is a sharp preview image that appears quickly in the Viewer.

Setting Preview Preferences

Aperture provides four preference settings for controlling previews. These settings apply to all libraries.

To open Aperture preferences
  • Choose Aperture > Preferences, then click Previews.

    The Previews pane appears.

Figure. Previews pane of the Preferences window.
  • “New projects automatically generate previews” checkbox: Select this checkbox to have Aperture automatically build and maintain previews for new projects you create in the current library (and, by extension, in new libraries). This checkbox sets the Maintain Previews For Project setting (described in Controlling Previews with the Library Action Pop-Up Menu) for each new project as it is created.
  • “Use embedded JPEG from camera when possible” checkbox: Select this checkbox to have Aperture use the JPEG thumbnail produced by the camera, if available.
  • “Share previews with iLife and iWork” pop-up menu: Choose whether to enable sharing of JPEG preview images with iLife and iWork applications.
  • Photo Preview pop-up menu: Choose the size (width and height in pixels) of preview images from this pop-up menu. The default setting is Half Size. The “Don’t limit” setting tells Aperture to make each preview the same size as the version. The other choices limit the preview to a size no larger than the specified size. A preview is never wider or taller than the version from which it is made. Aperture places asterisks (*) next to choices that match the resolution of your currently connected displays. Not all display resolutions are offered in the pop-up menu, so you may not see any asterisks.
  • “Photo Preview quality” slider: Use this slider to determine the compression setting used for the JPEG previews. The scale ranges from 0 (very high compression and relatively low quality) to 12 (very low compression and relatively high quality). The lower the quality setting, the less disk space a preview uses.

Note: Changing the preview quality and size settings does not affect previews that have already been generated. If you want to regenerate previews using the new settings, you must use the methods described in Controlling Previews with the Library Action Pop-Up Menu and Controlling Previews with Shortcut Menus.

Controlling Previews with the Library Action Pop-Up Menu

You turn automatic preview maintenance on or off on a project-by-project basis.

To have Aperture automatically update previews in a single project only
  1. In the Library inspector, select the projects whose images you want to maintain previews for.

  2. Choose Maintain Previews For Project from the Library Action pop-up menu (with a gear icon).

    A checkmark appears next to the Maintain Previews For Project menu command. Aperture will now automatically update previews when images are imported into the projects, as well as when versions are created or adjusted.

Note: Turning on automatic preview maintenance does not generate the previews. It only tells Aperture what to do the next time an image is imported or a version is created or adjusted. To generate previews, you can use the shortcut menus described in Controlling Previews with Shortcut Menus.

Controlling Previews with Shortcut Menus

You can control previews in projects by Control-clicking a project in the Library inspector and choosing an item from the shortcut menu that appears. In addition, you can control previews for single images or for a selection of images by Control-clicking images in the Browser.

In the Library inspector, you can delete all the previews for a project or update all the previews for a project.

To delete all the JPEG previews for a project
  • In the Library inspector, Control-click the project whose JPEG previews you want to delete, then choose Delete Previews from the shortcut menu.

To update all the JPEG previews in a project
  • In the Library inspector, Control-click the project whose JPEG previews you want to update, then choose Update Previews from the shortcut menu.

If previews are already up to date and you choose Update Previews, Aperture alerts you that no work is required. However, you can force the rebuilding of previews.

To force the rebuilding of JPEG previews in a project
  • In the Library inspector, hold down the Option key while Control-clicking the project whose JPEG previews you want to force Aperture to update, then choose Generate Previews from the shortcut menu.

In the Browser, you can select one or more images and either delete or update the JPEG previews.

To delete JPEG previews for an image selection
  1. In the Browser, select an image or group of images whose JPEG previews you want to delete.

  2. Control-click the image selection, then choose Delete Previews from the shortcut menu.

To update JPEG previews for an image selection
  1. In the Browser, select an image or group of images whose JPEG previews you want to update.

  2. Control-click the image selection, then choose Update Previews from the shortcut menu.

You can also force the rebuilding of previews for an image selection.

To force the rebuilding of JPEG previews for an image selection
  1. In the Browser, select an image or group of images whose JPEG previews you want to force Aperture to update.

  2. Hold down the Option key while Control-clicking the image selection, then choose Generate Previews from the shortcut menu.

Note: The commands for deleting, updating, and generating previews are also available in the Photos menu.

Viewing Preview Generation Progress in the Activity Window

Aperture renders preview images in the background; however, there may be times when you want to stop this operation. You can view the progress of the preview render operation, as well as cancel the operation, in the Activity window.

To stop the building of previews
  1. Choose Window > Show Activity.

    Figure. Activity window showing a "Building JPEG previews" task.
  2. In the Activity window, select the “Building JPEG previews” task, then click the Cancel Task button.

  3. Close the Activity window.

Note: Because slideshows that use the Best quality setting cannot begin until all preview images are up to date, preview generation is done in the foreground with a Cancel button to stop the operation. In all other cases, previews are created in the background.

Rescheduling JPEG Preview Maintenance

Preview maintenance can be rescheduled for projects in which automatic preview maintenance is turned off.

To reschedule JPEG preview maintenance
Do one of the following:
  • In the Library inspector, select the project whose JPEG previews you want to start updating again, then choose Photos > Update Previews.

  • Control-click the project, then choose Update Previews from the shortcut menu.

Note: Each time you open Aperture, it checks for out-of-date previews in those projects whose automatic preview maintenance option is turned on and then schedules the previews for regeneration. If you don’t want previews updated automatically, turn off automatic preview maintenance for your projects. For more information, see Controlling Previews with the Library Action Pop-Up Menu.

Rendering Preview Images

Aperture renders preview images in four situations:

  • When a library is upgraded—provided that the “Create previews for existing images” checkbox is selected in the Welcome to Aperture dialog

  • When an image is imported, or a version is created, rotated, or adjusted—provided that the Maintain Previews item is selected in the Library Action pop-up menu (with a gear icon)

  • When you Control-click the library, a project, or an image selection and choose Update Previews from the shortcut menu

  • Immediately before a slideshow, if the previews are not up to date, and the slideshow preset uses the Best quality setting

When rendering a group of preview images, Aperture uses the current application preference settings for compression quality and picture size, not the settings that were specified when preview rendering began. For example, if you have the quality set to 6, and then halfway through rendering you change the setting to 8, the previews that have not yet been rendered will be compressed at setting 8. Previously rendered previews are unaffected.

To update previews to use new size and compression settings
  1. In the Browser, select the images you want to update.

  2. Hold down the Option key while Control-clicking the image selection, then choose Generate Previews from the shortcut menu.

If you encounter performance issues, you can check the Activity window to see if Aperture is doing work in the background (choose Window > Show Activity). If you think that preview processing may be degrading performance, you can turn off automatic preview maintenance for that project and cancel the preview processing task underway. You can then generate the previews at a more convenient time.

Sample Workflows for Using Previews Effectively

There are several methods for using preview images efficiently and effectively.

Generating Previews for Projects You Intend to Keep Offline

A JPEG preview is displayed when a referenced image’s master is offline or cannot be found. This makes previews a great way of maintaining high picture quality while conserving the disk space that masters (especially RAW files) require.

To use previews for offline referenced images
  1. Make sure the external hard disk containing the referenced masters you want to keep offline is connected to your computer.

    If the masters you want to keep offline are currently stored on your computer, you must convert the images to referenced images and move the masters to an external hard disk. You can do this by selecting the project containing the images whose masters you want to keep offline, choosing File > Relocate Masters, selecting an external hard disk location for the masters, and then clicking Relocate Masters.

  2. Control-click the project containing the images whose masters you want to keep offline, then choose Update Previews from the shortcut menu.

  3. When the previews are built (you can check the status by choosing Window > Show Activity), you can disconnect the hard disk containing the masters.

Even though the masters are offline, you can browse, search, and assign metadata to preview images. You can even use the Loupe to zoom in on preview images, because they are high-quality JPEG files.

Generating Previews for Images Based on Rating

Another way to use previews is to create a search that displays only low-rated images. You can then build previews just for those images and take their masters offline (for example, burn them to a DVD). That way you still have good-quality images for all of your photos, without using a lot of disk space.

You can also create a search that displays only highly rated images and then build previews for those images only. This is a useful alternative for workflows in which the default thumbnail resolution is sufficient for low-rated images.

Generating Previews for New or Active Projects

Because previews are used by the iLife and iWork Media Browsers as well as by the Mac OS X screen saver, you can use previews as a way to distribute your Aperture pictures in movies, on the web, on DVDs, in slideshows, and in podcasts using the applications in iLife. You can also download your Aperture pictures to devices such as iPod, iTouch, and iPhone; import your Aperture pictures into iPhoto; or use them to create Pages documents.

To share previews with other applications
  1. Select the project whose images you want to share with other applications, then choose Maintain Previews For Project from the Library Action pop-up menu (with a gear icon).

  2. Make sure that Always is chosen in the “Share previews with iLife and iWork” pop-up menu in Aperture preferences (choose Aperture > Preferences, then click Previews).

  3. In the Library inspector, Control-click the project and choose Update Previews for Project from the shortcut menu.

When the previews are built, you can open any of the iLife and iWork applications and use your Aperture images.

Generating Previews for Smart Albums

You can create previews for images collected in Smart Albums. For example, you can create previews for highly rated images only. For more information about working with Smart Albums, see Grouping Images with Smart Albums.

To generate previews for Smart Albums
  1. Create a Smart Album and specify criteria for it using the Smart Album’s Smart Settings HUD.

  2. Click in the Browser, then press Command-A to select all the images.

  3. Control-click one of the selected images, then choose Update Previews from the shortcut menu.

Note: Previews for Smart Albums are not automatically maintained—automatic preview maintenance is a project-level setting only. In this workflow, you need to update the previews yourself periodically, by following the steps in Controlling Previews with Shortcut Menus. Aperture builds previews only for the versions that have changed, so you don’t need to determine which ones to update.

Determining Which Versions Have Previews

There isn’t a badge indicating if a version has a preview. You can Control-click the version and choose Update Preview from the shortcut menu to learn if a version’s preview is up to date. (If the version’s preview is not present or needs updating, Aperture will build it or update it.) You can also drag a single version out of the Aperture Browser and a plus sign (+) appears over the pointer, indicating that there is a preview to drag out. If a plus sign + does not appear over the pointer, no preview exists for the selected version.

Turning Previews Off

If your workflow does not benefit from previews, you can turn them off completely.

To turn off previews
  1. Choose Aperture > Preferences, then click Previews.

  2. Deselect the “New projects automatically generate previews” checkbox.

    This step turns off automatic preview maintenance for any new projects that you create.

  3. In the Library inspector, select all the projects, then choose Maintain Previews For Projects from the Library Action pop-up menu (with a gear icon), so there is no checkmark next to it.

    This step turns off automatic preview maintenance for your existing projects.

    Note: You need to perform steps 1 through 3 for each of your libraries.

  4. If you have already generated previews for some projects and do not want them, select all the projects in the Library inspector, then choose Photos > Delete Previews.

    This step deletes all previews that have been generated previously. Again, you need to do this for each library in which you have already generated previews.

Dragging and Dropping

When a version has a preview built for it, you can drag the image directly from the Browser to any application that accepts JPEG files, including the Finder, Mail, and most other applications. If the version doesn’t have a preview, dragging and dropping is disabled for that version (except within Aperture). If you are dragging multiple images, but only some of them have previews, only the versions with previews are dragged out.

Integration with iLife and iWork

You can use previews to distribute your Aperture pictures in movies, on the web, on DVDs, in slideshows, and in podcasts. You can also download your Aperture pictures to devices such as iPod, import your Aperture pictures into iPhoto, or use them to create Pages documents. The Media Browsers in the iLife and iWork applications support browsing Aperture libraries. For each version in the library, Aperture provides two JPEG files to iLife and iWork: a 240-pixel (longest dimension) JPEG thumbnail that is shown in the Media Browser, and the JPEG preview image (at whatever size you specified for it). If a version has no preview, the image is not made available to the Media Browser.

Note: When images are within stacks, only stack picks and album picks are shared. If you want iLife to have access to an image in a stack and it’s not the pick, you need to extract it from the stack or make it the pick.

Integration with Mac OS X Desktop and Screen Saver System Preferences

Like images in iPhoto libraries, images in Aperture libraries can be used for your screen saver, desktop picture, and Mail, through the same mechanism the Media Browser uses.

Displaying Offline Referenced Images

When a master is offline or cannot be found, Aperture draws the thumbnail image first, and then the preview if it is present. Because the preview is high quality, you can zoom and even use the Loupe.

Suppressing Preview Generation When Opening Aperture

When Aperture opens, it begins updating previews for those projects whose Maintain Previews For Project setting is turned on. (For more information about maintaining previews, see Controlling Previews with the Library Action Pop-Up Menu.) This can cause problems if a project contains damaged files or images in unsupported file formats. In Aperture, you can suppress preview generation when opening Aperture, allowing you to more easily identify the damaged image files. To do this, press the Shift key while opening Aperture. You can also cancel the current preview maintenance operation using the Activity window.

Note: If you have canceled a preview maintenance operation, the previews are not updated until another change is made to the image. To force Aperture to update the preview for an image, see Controlling Previews with Shortcut Menus. The next time you open Aperture, automatic preview maintenance resumes.