Previews, What Are The For, Are They Necessary?

The previews are used for two purposes:

• to speed up browsing your library - otherwise it will be slower to browse projects and albums,
• to make your Aperture library accessible to other Applications, e.g. Desktop and Screensaver, Photo Browser in Mail; generally the iLife and iWorks applications use the previews, to let you drag and drop your images into documents. I like to have this quick access to my pictures when I prepare documents in iWeb or keynote, without having to open aperture first.

If you do not need any of this, you may forsake the generation of previews and delete any previews you generated.

Regards

Léonie

You can safely turn off the generation of previews and delete the previews that are already generated if you won't be acessig the Aperture library from any other application via the media browser.

As Lónie mentioned previews are also used to speed up the initial loading of images but to be honest I've never noticed a great difference between viewing images with and without previews.

There is also the issue of being able to view the images in your library if the masters are offline. If you have referenced masters and the masters are on a disk different then the disk the library is on this could be a problem but if you don't plan to work this way then you'll be OK.

To delete the previews currently generated select all the images in your library then go to Photos->Delete Previews. To prevent the creation of new previews turn off New Projects Create Previews in the Previews preference pane. You may also have to turn off the Maintain Previews for all projects located in gear menu in the Library, here:

I beleive the setting in Preferences only affect new projects this one affects current projects.

Of course if you find not having the previews a problem you can always turn them back on and regenerate them. You can also selectively generate previews for those images you want to share.

regards

Great question. To add a few small but perhaps worth-considering points to Frank's and Léonie's thorough answers. IME I needed Previews for some Images, and found it "cheaper" to provide the drive space for the Previews than to keep track of which Images needed/did-not-need and had/did-not-have Previews. After a bit of experimentation I settled on a size for all Previews, and generated (and set to be generated) Previews for all Images.

1. I prefer to "pay the price" of having large previews as a kind of tertiary redundancy. Each Library (and every back-up of each Library) holds usable image-format files of all of the Images in it (these are, of course, the Previews). This makes me happy. (If I had no Referenced Masters I might not do this.)
2. Large Libraries -- and particularly large Libraries of Images with large RAW Masters -- become almost un-usable without Previews (IME).
3. If a Library is on a laptop, at some point Previews will be necessary. The Library will outgrow the available drive space, Masters will be converted from Managed to Referenced, and the user will want to have Previews available when the Masters are off-line.
4. A good-size Preview can in almost all instances be used "in a pinch". As everyone knows, things fail, power goes out, cables get frayed or forgotten, etc. The Preview may not be a first choice, but as a second choice it is infinitely better than no image at all.
5. This is just a guess, but it may be that the Preview is what is initially scanned for Faces, and then the whole Image is scanned when a second scan is forced. I don't know what effect not-generating Previews will have on Faces.

Almost all of this comes down to the costs associated with storage. Aperture performs well with Previews. My experience is that the cost of storing Previews is always less than the cost of administering a Library without Previews -- but my experience is using a laptop as a primary computer and setting up Libraries with at least some Images having Referenced Masters. In your (1 Open Loop) case, Previews could represent more cost than value. Similar to what was suggested above, I recommend deleting all your Previews and seeing how that works for you. You can always regenerate them.

Let us know what you find out.

Yes to your questions. If you don;t have previews anything using the media browser will not be ale to get images out of your library.

For mail you can do the email from within Aperture and that will work.

Just remember if the masters are referenced and you access them from the finder what you will be getting is just that, the master. Any adjustments you made to the image will not be available unless you export the version from the library.

So, if I don't have any Previews, I can't assign a Desktop or Screensaver using Aperture. But, since my Library is Referenced, I can simply browse to the Finder location.

The Finder only shows you the raw masters, not your edited versions. Mymaster images would be quite useless as Desktop or Screensaver picture. Before I process them, straighten the horizon, crop them, adjust the lighting and contrast and never would show them off as screensaver or include in a document. If you want to access your edited versions outside Aperture you will need the previews. But perhaps your images are perfect right from the beginning, I am not that good a photographer.

That is why keeping previews might speed up Aperture - you do not have to do the image processing each time again when you browse the images.

These continue to be good questions. The User Manual provides a better answer than we can give you here. Read this section on Previews, and then post further questions:

Working with Preview Images

Adjustments cannot be made on Images whose Masters are off-line or missing.

No when the image you see is a full resolution image made up of the master plus the adjustments you made to it. Adjustments are always done to the master which is why images with missing masters can;t be adjusted.

You just need to select all the images in the album and ctrl-click them: In the pop-up menu you should see: Update Preview. Select that, and for all images in the album previews will be created.

You don't have to do that from the project.