While testing Lightroom, I’ve decided to set my iCloud Photo Library to Optimize Storage. That way, it won’t take up very much space on my devices because it will dynamically decide which photos to keep at full resolution, while still retaining the benefits of automatically syncing photos between my iPhone and iPad in the background.
Optimize Storage, if done right, is actually what I’d like most from a cloud photo service. I want the benefit of having my pictures within easy reach, but I don’t want to necessarily store everything at full resolution locally. What would make the most sense to me would be to have thumbnails of my images that are sized exactly to the device screen, which means 2732×2048 for the 12.9” iPad Pro and 1920×1080 for my iPhone 6S Plus.
This is the way I understand Photos on OS X and Lightroom to work. They don’t just display a small thumbnail and a medium thumbnail, they generate these extra files in advance to speed up the experience of browsing through a large library of photos. I know that iOS generates the tiny thumbnails that are seen in the Years, Collections, and Moments views, but I’d love to see Optimize Storage also generate fullscreen previews for every single photo in my library. This would let me view any photo in my library regardless of online status, but it wouldn’t take nearly the same amount of space as an actual 6000×4000 (24 Megapixel) shot.
Unfortunately, this doesn’t seem to be the way that iCloud Photo Library’s Optimize Storage works most of the time. I do have fullscreen thumbnails for a majority of my photos (possibly due to my iPad Pro’s previously setting of Download and Keep Originals), but some of them don’t even have a large thumbnail downloaded.
Try as I might, I haven’t really been able to figure out exactly how the algorithm decides which photos to create thumbnails for…and which photos will be blurry messes when I try to view them fullscreen.
Skipping around at random through 13 years of photographs hasn’t yielded very conclusive results. I find I can sort through 10 images from 2004 without having to load a fullscreen thumbnail, and the 11th photo will require a download to even render properly.
There does seem to be a change in how iCloud is downloading the files, though, and that does give me some hope. As I understood it previously, the Optimize Storage setting would just provide me with thumbnails big enough to populate the Moments view, and it would just try to keep the past month’s photos fully loaded.
If I wanted to view an undownloaded photo, I’d select it and just wait while iCloud downloaded the entire photo. It was smart enough to also download any directly adjacent photos, but not the photos that were twice-removed from my selected photo (e.g. the photo that’s two swipes away). What this resulted in was an experience with a lot of waiting and loading. I’d wait for a download to finish, view a shot, swipe to see a second shot, and then wait again as the third photo downloaded fully from iCloud.
This seems to have changed for the better in a recent iOS 9 update, but I can’t tell quite which one. From my testing, Photos now seems to keep fullscreen thumbnails for most of my photos, and will dynamically download a fullscreen thumbnail for any photo that still requires one. These thumbnails are good enough for viewing and can even stand a little pinch-zooming for better viewing.
Another new detail is that iCloud will start a background download as soon as you pinch into a photo. Once this download completes, you’ll have an even larger preview on your device to show the picture at a 100% crop. This difference isn’t immediately noticeable, but if you’re checking for sharpness in a small section of your shot, you’ll see that the picture will jump into razor sharpness when the download finishes.
The funny thing is that this isn’t necessarily the full resolution file yet. When I press Edit on pictures that have the fullscreen and 1:1 thumbnails, I can often still see an additional loading circle. I have to wait a few seconds for the full 12.2 MB JPEG to download, and then I can edit it.
This is all a lot of guesswork on my part based on testing with my own 60 GB library. It would really help if Apple provided a little more documentation on how this feature worked, and had indicators to show which photos were downloaded in full. That said, it’s good to know that if Lightroom doesn’t turn out for me in the long run, I have a decent alternative in iCloud Photo Library and Optimize Storage now.