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As far as I can tell, iOS does some really strange things when it comes to compressing the media in your Photos app.

It seems that any time you use the "share" sheet, it's compressing your photos slightly, even when using AirDrop. Comparing a photo transferred via Airdrop to one transferred via copy/pasting in Windows Explorer, there's a fairly significant file size difference (2.98MB vs 3.75MB). At first I thought this may be due to some sort of lossless compression, but then I compared some videos, and the actual bitrate on the video streams differed when transferred via USB vs any other app or Airdrop (12mbps vs 14mbps).

Going to the settings app and changing the "Transfer to PC or Mac" setting to "Keep Originals" under the photos section makes no difference.

As far as I can tell, transferring via USB to a Windows PC is the only way to do it. But...this can't be the only way, right? There should be a proper way to do it within the Apple ecosystem. But yet, MacOS won't even entertain the idea of letting you transfer photos via USB lightning cable as long as you have iCloud photos enabled. And iCloud photos' option of downloading the "unmodified original" from the web app is a complete misnomer, as a 3.75MB photo comes down as 1.95MB, and full HD videos actually come down in 720p.

Anyone with any insight as to how iOS's compression system works would really help me out here. Thanks in advance.

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Alright, it seems I've made a bit of a deduction mistake - turns out changing "Automatic" to "Keep Originals" under Photos in the Settings app makes all the difference. Depending on which option is checked, the files will show up differently in Windows Explorer. The "Transfer to PC or Mac" section of the Photos menu of the Settings app.

"Automatic" makes them show up as .jpg files. "Keep Originals" makes the photos show up as HEIC files. That's the reason for the size difference (.heic files are much smaller).

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Image Capture

There is a way to transfer photo files from the iOS device to your MacOS device by way of running the Image Capture app from the MacOS device. This application has Import by selection from a manually selected range of images in the UI or Import All functionality that copies everything off the device.

Image Capture screenshot

The app copies all the metadata for the image files as well including the creation and modification dates of the original file present on the iOS device. You may be fooled a bit in Finder where the files appear to be created new, however something eventually updates the file attributes I've found and you see the old dates show up after some delay or from a UI refresh or something in Finder. Image Capture does differ in behavior from AirDrop in that it gives you the base unedited files and if a filter or something was applied to it such as Portrait etc, then the image copies over by itself but also with a *.AAE file, or Apple Adjustments and Edits Sidecar, eg

  • IMG_5310.JPG
  • IMG_5310.AAE

With AirDrop the final rendered filtered image gets copied over, which is often the desired outcome. I don't know of any application which can take the base image and its adjustments and edits and recreate what you see in the photos app. Another difference is that AirDrop creates a selection of all the transferred files into your Downloads folder which makes it very easy to create a new folder with the selection as it came off your device. This is a very useful feature because of Apple's file naming scheme that has a cycle of 10000 images, ie the 4 digits in IMG_XXXX.JPG. If you transfer over a big batch of images you may hit a name collision and could potentially overwrite an earlier photo with the same name as another.

Here's a sample of a spot checked file I just tested with a transfer just now. Do note the matching pixelization and exif metadata and the file attributes agreeing across both sides. Same for the file size.

Image Capture transfered photo file info vs iOS image info

Photos Configuration: TRANSFER TO MAC OR PC

The last section in this support page covers a bit about the compression

Importing this media via USB

When you import HEIF or HEVC media from an attached iOS device to Photos, Image Capture, or a PC, the media might be converted to JPEG or H.264.

You can change this import behavior in iOS 11 or later. Go to Settings > Photos. In the TRANSFER TO MAC OR PC section, tap Keep Originals to prevent the media from being converted to JPEG or H.264 when importing.

https://support.apple.com/en-us/HT207022

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