Help- Artifacts/Corruption in several Photos

Thanks for your reply. I eventually found that using the Photos Export command and then using Preview to convert from HEIC to JPG was unnecessary. Instead I created a folder on the Desktop and click/dragged the hundreds of artifact affected photos from the Mojave Photos app to the newly created Desktop folder - that action alone converted the HEIC files to JPG without resorting to Preview. The converted JPG photos were indeed artifact fee. Subsequently I used a folder action to rename the new JPG photos as the Photos app would not have otherwise allowed re-importation, having identified the photos as already existing in the app's catalog. I choose to use Find & Replace in the following manner: Find "." & replace with "-2.", resulting in the following naming format "IMG-1149-2.jpg”. Of course I now have duplicates and can safely delete the HEIC artifact files as I choose.

He can use his Mac to convert from HEIC to JPG (Using Preview), I just checked and there are no artifacts in the generated JPG.

Thank you for the reply. As mentioned above, I erased my SSD, re-installed Mojave fresh, then re-did the test, so there is no additional software installed aside from Apple's.

Graphics Card: NVIDIA GeForce GTX 775M 2048 MB

Apple's diagnostic test (pressing D) doesn't show any issues, I know Apple store tech's have a more extended one but diagnosing Graphics card issue is tough.

And voila, I believe I found something, its HEIC vs JPG... OP, please try switching on your iPhone X to Compatible mode which will create photos in JPG format. I have taken two photos just now and recorded the video as I am switching between the HEIC and JPG photo in Finder. The JPG photo exhibits no artifacts while the HEIC does.

Now that does NOT explain why this issue does not happen with many other HEIC users so there must be something still to do with the Mac 😕

My card is different:

AMD Radeon R9 M370X 2048 MB

Intel Iris Pro 1536 MB

It may be the combination of a certain graphics card with the HEIC compression.

Both JPEGs and HEIC images have a lossy compression, but the algorithms are different, and they will give different artifacts, if some bits of the image get modified due to faulty memory modules or problems with the graphics card. That you are only seeing the artifacts in normal mode points to the hardware, if your Mac software is still squeaky clean after the clean install.

If your HEIC photos have all been taken on the iPhone, you may want to check them, while they are still on the iPhone. Are you seeing the same corruption, if you are zooming in on the photo on the iPhone? Before it has ever been touched by the Mac? Or do the artifacts only appear after transferring the photo to the Mac?

As a further test: You could try to convert a JPEG that is fine to a HEIC file on your Mac. Preview can export in the HEIC format.

I think at this stage it’s fair to say that there is an issue with displaying/previewing/editing HEIC photos on certain subset of iMac GPU on Mojave. (GeForce GT family?)

Those of us on Mojave/GPU “bad combination” can fall back to JPG until hopefully Apple investigates further and hopefully fixes something.

I do not think it’s a widespread issue across all iMac GPUs because there would have been much more roar!

Restarting worked. Thanks @jorel

Once upgraded to 10.14.2 the artifacts have disappeared. But I do need to edit each one & make some additional adjustment to the image for it to go away.

Interesting, I should have tried this first, by booting into safe mode, the issue does NOT happen.

Safe Mode disables accelerated graphics. Perhaps all of you who are seeing this problem should compare the models of the graphics cards.

If it is not the graphics card - safe Mode also disables these features: Use safe mode to isolate issues with your Mac - Apple Support

• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions
• Prevents startup items and login items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files

So it would be good to check the kernel extensions and startup items installed by older software.

I am more and more convinced that this problem is specific to certain iMac models from around 2013.

I am not seeing this problem on my MacBook Pros in Photos 4.0 on Mojave, but two days ago I took the plunge and upgraded my iMac as well to Mojave. And now I am seeing corrupted thumbnails and artifacts for the heic images, not only the images from my iPhone X, but also the images I converted to HEIC on my MacBook pros. My iMac is an iMac 27", late 2013.

Same problem here on Mojave 10.14.1 (18B75). I took some pictures yesterdag on a family party. When I preview them in Finder with Quick Look the artifacts are most apparent with HEIC images. I've found the following:

1. Export on Mac from Photos HEIC to JPG results in pictures with screen artifacts
2. Exporting to a different image format (I tried TIFF) there are no artifacts
3. "Export Unmodified Original..." also results in pictures with artifacts
4. Sometimes the artifacts disappear when peviewing them again with Quick Look (cursor up/down in a list of pictures)
5. Artifacts appear top and left side and bottom and right side of the image

I use a Mac Pro 5,1 with an Nvidia GTX680 Mac edition video card with standard macOS drivers.

I am seeing the same on my iMac 27", late 2013 after official release of macOS 10.14.2. I can now edit heic images, and the thumbnails remain normal, after I fixed them by rotating them back and forth.

I noticed that all my photos that have been edited show these patterns. If I revert the photo to the original, the patterns disappear.

Yes really 😉 The issue may have to with rendering HEIC pics. I converted few HEIC to JPG and didn’t observe any artifacts.

Mojave latest 10.14.2 seem to have fixed the issue. I took a HEIC photo and previewed it before upgrading, artefacts were there, after upgrade they are gone for the image.

we can switch to JPG on iPhone and all is well at the expense of more storage consumption on the iPhon

And at the expense of more storage consumption on the Mac. I have converted most of my image files on my Mac to HEIC and are storing the originals on external drives. This way I can keep 50000 photos in my iCloud Photo Library without having to revert to Optimize Storage on the iPhone. I like HEIC. It does not only save storage, it also saves bandwidth when transferring the files between devices.