How To Fix Mac Image Preview Thumbnails Not Loading Issue

Preview is the default image viewer app on Mac that allows you to quickly view images, PDFs, and other files. It shows a thumbnail preview of supported image formats like JPG, PNG, GIF, etc. in the Finder, so you can easily identify files without opening them. However, sometimes these thumbnail previews stop working and you only see generic icons instead.

If you are facing this issue of image preview thumbnails not loading on your Mac, don’t worry – there are a few things you can try to fix it:

1. Check Finder View Settings

The first thing to check is whether preview thumbnails are enabled in Finder or not. Here’s how to verify this:

  • Open any Finder window
  • Go to View > Show View Options (or press Cmd+J)
  • Make sure Show icon preview is checked

If this setting was disabled, check the box to re-enable it. Now image thumbnails should start appearing again.

2. Force Quit QuickLook Thumbnails Agent

Sometimes the process responsible for generating thumbnails – com.apple.quicklook.ThumbnailsAgent – can get stuck. You can force quit this process to restart it:

  • Open Activity Monitor (in /Applications/Utilities)
  • Search for com.apple.quicklook.ThumbnailsAgent
  • Select it and click the “Quit Process” button
  • Also quit Finder application
  • Relaunch Finder

This will restart the thumbnail generation process and reconstruct all the missing previews.

3. Reset Finder PLIST File

Corrupted Finder preferences can also cause issues with preview thumbnails. Here’s how to reset these preferences:

  • Go to Finder > Go > Go to Folder (Shift+Cmd+G)
  • Enter ~/Library/Preferences and press Enter
  • Look for com.apple.finder.plist file and move it to Trash
  • Empty Trash and restart your Mac

Finder will regenerate a fresh PLIST file with default preferences, which should take care of any corrupted settings that were causing problems.

4. Update Your macOS Version

Sometimes bugs in your macOS version can also manifest as image preview issues. Ensure your system is updated to the latest version:

  • Go to Apple Menu > System Preferences > Software Update
  • Install any available updates, including minor updates
  • Restart your Mac after updating

Updating macOS can fix many bugs and issues that may be causing Preview problems.

5. Boot Into Safe Mode

Booting in safe mode loads a minimal version of macOS without any third-party extensions. This can help isolate issues caused by apps/extensions:

  • Shut down your Mac
  • Power it back on and immediately press the Shift key
  • Let go of Shift once you see the login screen (with ‘Safe Boot’ on top)
  • Log in normally and check if previews work now

If yes, some third-party app/extension was the culprit. You can disable startup items one-by-one to identify it.

6. Create a New Test User Account

Sometimes issues can be isolated to your user account. Creating a test account will help verify that:

  • Go to Apple Menu > System Preferences > Users & Groups
  • Click the lock icon and enter admin password
  • Click the “+” icon below and create a test user account
  • Log out from your account and log in to the test account
  • Check if previews work there or not

If they work in the test account, it points to some file/configuration in your user profile being the issue.

7. Reinstall macOS as a Last Resort

If you have tried everything else to no avail, reinstalling macOS may help fix any underlying issues. Note that this will erase your drive, so first backup your data. Follow this guide from Apple to reinstall macOS cleanly.

Conclusion

Preview not showing thumbnails for images is a common annoyance on Macs. In most cases it can be fixed by simple troubleshooting like resetting Finder PLIST file or updating macOS. For advanced issues, create a test user account to isolate the problem before reinstalling macOS as a last resort. Hopefully the steps outlined in this article will help you get back your precious image previews!

Frequently Asked Questions (FAQs)

Here are some common queries related to this issue:

Q. Why did my image previews suddenly vanish in Finder?

There can be a few reasons for this – Finder view settings may have changed, the thumbnail agent process crashed, some extension/app is interfering, or your user preferences have become corrupted over time.

Q. How can I get image thumbnails back in Finder?

Follow the troubleshooting steps outlined in the article like resetting PLIST file, booting into Safe Mode, creating a test user account etc. One of them should definitely bring back missing previews.

Q. Will reinstalling macOS delete all my data?

Yes, reinstalling macOS will erase your entire drive. So before doing it, ensure you backup all your important documents, photos, emails etc. to an external hard drive.

Q. What image formats does Preview support?

Preview can render thumbnails for common image formats like JPG, PNG, GIF, TIFF, PSD, BMP etc. For unsupported formats like WebP it will show a generic icon.

I hope this comprehensive guide helps you resolve the ‘image previews not loading’ issue on your Mac! Let me know if you have any other questions.