In Aperture I understood the process to be that changes made in post processing where stored as "instructions" (not sure of real term) to be applied to the original and in that way saved space for storage over iPhoto where it appeared to me that a duplicate copy of the photo was made.

I'd like to understand what the new Photo does. I would bet the same as iPhoto?

2 Answers 2


For Photos.app, don't consider the edits necessarily edits. While looking through the file architecture one day, I found that what they're doing is storing the original and simply adding layers of "edits" which are much more like layers of removable filters.

The original stays 100% in tact until you export it to a separate file where Photos will process those layers into an image.

The only way you would lose originals and be stuck with the edited versions is if you specifically, in this order:

  1. exported your edited version
  2. deleted the photo from Photos.app
  3. deleted your Photos.app Trash
  4. put the exported version back (technically for the first time) into Photos.app.

Photos.app uses non-destructive edits, meaning that yes, essentially a set of instructions for applying edits is stored alongside the original bitmap, as opposed to duplicating the bitmap with the edits applied. Most likely it is stored as metadata within the file as opposed to a separate file. You can revert to the original at any time.

You can also duplicate the image as a kind of "snapshot" - any edits made to the point of duplication will be applied to the duplicate image (again, non-destructively), but both the initial image and the duplicated image are still pointing to the same bitmap on disk. Any further edits made to either image will not be reflected in the opposite image, and you can revert either to the unedited original at any time.

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