iPhone photos duplicated with lower resolution after syncing to iMac

That is the expected behavior. The manual syncing is not symmetric.

• When we sync photos from the Mac to the iPhone, an optimized, smaller version will be synced to the iPhone. This optimization is specific for each destination device.
• When we sync photos from the iPhone to the Mac, the full resolution files will be saved to the Mac.

We can create low resolution duplicates, when we edit synced photos on the iPhone. To be able to edit a synced photo, the iPhone has to save the synced photo (a smaller optimized version) to the iPhone, and when we sync the iPhone again with the Mac, the saved, optimized smaller version will be treated as a new photo and downloaded to the Mac. Better not edit synced photos on your iPhone - just view them there, but make all editing on the Mac.

To get rid of the synced duplicates, sync again photos from your Mac to the iPhone, but exclude the albums with photos that are already on your Mac.

ernold wrote: … photo on iPhone, imported to Photos in iMac, synced back to iPhone, the photo is now a lower resolution duplicate in the iPhone. The duplicate is not editable and is of lower resolution and size. I can delete or edit my original but not the copy. Two of everything in my Photos library.

That sounds right. Why did you do this? What was your objective.

ernold wrote: photo on iPhone, imported to Photos in iMac, synced back to iPhone, the photo is now a lower resolution duplicate in the iPhone. The duplicate is not editable and is of lower resolution and size. I can delete or edit my original but not the copy. Two of everything in my Photos library.

Following that procedure should not reduce the resolution unless you made a step you failed to mention. The fact that photos (and videos) synced to your phone from your Mac are not editable (or deletable) by the phone is expected behavior; you have to manage those on the Mac and repeat the sync to the phone. This behavior is left over from earlier days when library management was done on computer and downloaded to simpler devices for display.

léonie wrote:

When we sync photos from the Mac to the iPhone, an optimized, smaller version will be synced to the iPhone. This optimization is specific for each destination device.

Thank you for reminding me of that, léonie!

ernold, that optimization was important back when the receiving devices were stupid endpoints like iPods, but maybe not so good when the targets are full-fledged computers in their own right. Today, we may be printing directly from our iPhones/iPads, driving external screens, or passing images along to others. If those uses are important to you, cable sync may not be appropriate for your situation.