Suppress preview generation
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 Automatically manage previews.) This can cause problems if a project contains damaged files or images in unsupported file formats. 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 photo. To force Aperture to update the preview for a photo, see Manually manage previews. The next time you open Aperture, automatic preview maintenance resumes.
While Aperture is open it 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.
Stop preview generation
Choose Window > Show Activity.
In the Activity window, select the “Generating preview” task, then click the Cancel Task button.
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.
Turn off previews
If your workflow does not benefit from previews, you can turn them off completely.
Choose Aperture > Preferences, then click Previews.
Deselect the “New projects automatically generate previews” checkbox.
This turns off automatic preview maintenance for any new projects that you create.
In the Library inspector, select all the projects, then choose Maintain Previews For Projects from the Library Action pop-up menu , so there is no checkmark next to it.
This turns off automatic preview maintenance for your existing projects.
Note: You need to perform steps 1 through 3 for each of your libraries.
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 for Items.
This deletes all previews that have been generated previously. You need to do this for each library in which you have already generated previews.