How does Mac Photos store edited photo information?

[tractorcat]

How does Mac Photos store the extra information associated with editing pictures?
Does it store two copies on the drive, the original and the edited?
Or does it only store the original and the edits data and then render the image with the edits data upon viewing/exporting/etc?

 

[NoBoMac]

The latter, sorta. If you modify the actual image, there is a copy made. But meta data like description, location, tags, title, etc. are kept in a database and tagged to the photo on export. Anything that came over from the camera is on the imported file.

So, a bit of a mish-mash.

 

[tractorcat]

The latter, sorta. If you modify the actual image, there is a copy made. But meta data like description, location, tags, title, etc. are kept in a database and tagged to the photo on export. Anything that came over from the camera is on the imported file.

So, a bit of a mish-mash.

Thanks for the reply. So seeing as the description, tags, and other EXIF related data etc are of generally a fairly small size, editing a photo causes it to take nearly twice as must disk space?

 

[NoBoMac]

Thanks for the reply. So seeing as the description, tags, and other EXIF related data etc are of generally a fairly small size, editing a photo causes it to take nearly twice as must disk space?

Or more. Need to keep a copy of the original, if you want to revert back.

Just ran Photos' "enhance" function on a picture. Before/after sizes of the images.

Before: 236769 May 26 20:42 IMG_0481.HEIC
After: 1262775 Jul 29 07:59 ./resources/media/version/1c/00/fullsizeoutput_1ce5.jpeg

 

[tractorcat]

Or more. Need to keep a copy of the original, if you want to revert back.

Just ran Photos' "enhance" function on a picture. Before/after sizes of the images.

Before: 236769 May 26 20:42 IMG_0481.HEIC
After: 1262775 Jul 29 07:59 ./resources/media/version/1c/00/fullsizeoutput_1ce5.jpeg

Ok, awesome, thank you for testing that! Though the near 5x increase is surprising...

 

[NoBoMac]

Yeah, odd that that big, as HEIC vs JPG should be about 2x. Crummy JPG render engine in Photos?

JPG to JPG should, guessing, keep roughly same size post edit. Seem to recall seeing that in the past.

 

[ApfelKuchen]

Let's clarify something... Editing updates the Preview image. Preview is a JPG used to display the current (edited) version of the image on-screen. This avoids re-rendering the edits every time you open an image.

Need to keep a copy of the original, if you want to revert back.

Something very important - the original Master image is never modified. That's the whole point of the system. Non-destructive editing. There is no need to save a copy of the original if you want to revert. You would need to save a copy of an edit in order to preserve the edit prior to reverting to the original. The normal way to do this is to Duplicate an image. Afterwards, you can revert the duplicate and use it to create an alternate edit.

Previews are going to be smaller than most Masters; significantly smaller if you shoot RAW. There is only one Preview for each Master image (and one Thumbnail), unless you Duplicate an image. At that point, you still have one Master, but now have two Previews (and two sets of the metadata files that go with each version of the image).

 

[tractorcat]

So as a follow up to this, it appears that Mac stores edits in separate .aae files in some cases and in the photos database in others, regardless, this means that only the Master photo is stored, and then the edits are stored as instructions, not as edited pictures.
https://discussions.apple.com/thread/250288805?answerId=250540789022&page=1

Interesting that this seems to conflict with NoBoMac's findings of a large increase in file size after editing the image, as a file only storing the edit instructions' size should be negligible.

 

[NoBoMac]

Re: file size growth: that might be an odd one in that it was a HEIC image. Since it's a compressed format, it got output as a JPG in Photos after an edit. Basically, became uncompressed.

Just happen to have Photos up and did another little experiment. Took an old JPG from an iPhone and a RAW image from an Olympus camera. Copied them outside of Photos library, renamed, imported as "new" photos. Simple edit of "enhance" on both of them. RAW became a JPG and smaller (this is pretty much known would happen), the JPG grew by about 0.85MB.

Before:

2321069 Jun 24  2018 Hoho1.JPG
14822042 May 12 09:35 Foop1.ORF

After:

3176123 Aug  5 11:55 fullsizeoutput_1ce9.jpeg
7212318 Aug  5 11:55 fullsizeoutput_1cea.jpeg