Finder stops rendering thumbnails after opening folder with DNG files

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Level 1

14 points

Finder stops rendering thumbnails after opening folder with DNG files

After updating my Mac to macOS 15 I have this problem and it still isn't fixed in 15.3.2. I wasn't like that on macOS 11, 12, 13 and 14.

I have a lot of images of mostly common types like JPG PNG WEBP, and I can browse folders with them just fine. I can easily find any image just by looking at thumbnails in Finder.

However, if I open any folder that contains at least one DNG file (digital negative), Finder will stop generating thumbnails for any new unseen images (already generated thumbnails will remain). Files of other types are not affected.

Process "ImageThumbnailExtension" will start to use crazy amounts of CPU (up to 400%) and RAM (up to 12Gb). Fans will start to spin too. It will do that for hours, even though I may have just opened a folder with 1 DNG file of 50Mb in size.

I have tested this on MacBook Pro M1 Max 32Gb, MacBook Air M1 8Gb, iMac M1 8Gb, with macOS 15.0 up to 15.3.2 (and all versions in between). I also did plenty of tests in virtual machines (Parallels).

You may say it's due to some 3rd party apps - but VMs have 0 3rd party apps, are fresh after installation, have all default settings, and still have this problem.

To demonstrate the problem I've recorded this video, please watch:

Finder won't render image thumbnails after opening folder with DNG files

MacBook Pro 16″, macOS 15.3

Posted on Mar 22, 2025 3:02 AM

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Answer 1

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Kamino_Ramos Author

Level 1

14 points

May 12, 2025 1:05 PM in response to Kamino_Ramos

Happy to say that update 15.5 finally fixed the issue, somewhat. Thumbnails of DNG files still sometimes fail to generate (all I see is black square). But at least "ImageThumbnailExtension" won't use all my CPU and RAM, and any other image files now render properly, just like it was before this problem ever occured.

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Answer 2

May 15, 2025 4:55 PM in response to Kamino_Ramos

The 15.5 update fixed my thumbnail issues, and the CR3 files, as well as other raw formats, are now working. It's really funny that my earlier call to the person from Canon tech support proved to be correct...it was an Apple thing!!

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Answer 3

Kamino_Ramos Author

Level 1

14 points

May 12, 2025 1:11 PM in response to LeoDodier

I believe that something about specific dng files might be the problem, but I'm not sure that it's color profile. Now that update 15.5 fixed high cpu/ram usage and rendering of other images after dng failure, I can view folders with my dng's. I see that some of them render just fine while others appear as black squares. However according to file info, both examples use same color profile - P3. Or perhaps it's due to file having wrong profile assinged, that's the problem... Similar to how if you rename png to jpg (changing extension while keeping file the same) it will fail to generate a thumbnail, since macOS 15.0.

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Answer 4

dialabrain

Level 10

135,947 points

Mar 22, 2025 3:35 AM in response to Kamino_Ramos

No problem on my M1 MBA.

Try booting into Safe Mode then restart normally. Sometimes that will fix anomalies.

Start up your Mac in safe mode - Apple Support

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Answer 5

May 11, 2025 6:14 PM in response to Kamino_Ramos

I have a M1 MacBook Pro, and use an external BenQ SW272Q with a custom calibrated color profile. After a long call to Canon, they said it was an Apple issue. First call to Apple and they said it was a Canon thing. Second call to Apple , they said it was a custom color profile issue and it looks like they were right...kind of. When I change the color profile, and sometimes even resolution (or both), the CR3 raw file will show the photo in the thumbnail. When I choose another file, that thumbnail turns black again. I can't figure it out, but it appears the color profile is the issue. I'm not a real tech guy, so if anyone can help, that would be awesome! Thanks in advance.

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Answer 6

dialabrain

Level 10

135,947 points

Mar 22, 2025 4:20 AM in response to Kamino_Ramos

FWIW, after I had done a few tests, suddenly new images I downloaded to my desktop only showed generic icons. I don't know if it's related to your issue or not. I had to do a restart to fix it.

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Answer 7

Kamino_Ramos Author

Level 1

14 points

Mar 22, 2025 5:21 AM in response to dialabrain

Well, that's the thing. In my case restart always helps, but only until I open another folder with DNG files. What about Activity Monitor? ImageThumbnailExtension process is there? High cpu usage, lots of ram? Perhaps your memory wasn't filled at first, but after a couple of images it was and then there were generic icons?

dialabrain wrote:

FWIW, after I had done a few tests, suddenly new images I downloaded to my desktop only showed generic icons. I don't know if it's related to your issue or not. I had to do a restart to fix it.

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Answer 8

dialabrain

Level 10

135,947 points

Mar 22, 2025 3:17 AM in response to Kamino_Ramos

Normally I don't work with RAW or DNG files. Just as a test I downloaded a few Nikon D850 RAW files and converted them to DNGs. I can't reproduce the problem on an M3 iMac running Sequoia 15.3.2.

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Answer 9

dialabrain

Level 10

135,947 points

Mar 22, 2025 3:24 AM in response to Kamino_Ramos

Sorry, I should have included an open folder of other images; jpgs, pngs, webps, etc. in the screen shot but I didn't think if it. As you can see it's still early here.

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