Why Are My Thumbnails Not Showing on Mac?

The Universal Reset: Rebuild the Thumbnail Cache

Finder's icon-grid thumbnails and the full-size preview you get by pressing Space both come from the same Quick Look generator system, cached per user in a randomized folder under /var/folders named com.apple.QuickLook.thumbnailcache. A corrupted or stale entry in that cache can make one specific file, or an entire folder, show a stale or generic icon even though the underlying file is perfectly readable.

Open Terminal and run the two commands below, then relaunch Finder (hold Option, right-click the Finder icon in the Dock, choose Relaunch). This touches nothing about your actual files; it only tells macOS to redraw cached preview images the next time they're needed, which costs a few seconds per folder the first time you open it again.

qlmanage -r cache qlmanage -r

If that clears it, you're done. If specific formats are still blank, the cause is further down this list.

HEIC Photos: When the Thumbnail Never Builds

Most HEIC photos straight from an iPhone or iPad preview fine, since macOS and iOS share the same HEIC encoder. The cases that fail are usually photos that passed through a different tool, an older third-party editor, a batch converter, or an AirDrop from an app that repackaged the file. A reported case on the libheif open-source project's own GitHub tracker found a sharper version of this: HEIC files re-encoded from JPEGs with odd pixel dimensions would not open in Preview at all, with macOS reporting the file as damaged, while the exact same files converted cleanly to JPEG with a different tool. The maintainer traced it to a mismatch in how the two encoders handle non-even dimensions, not file corruption, and shipped an encoder fix. The practical lesson carries over to thumbnail-only failures: a HEIC that previews fine elsewhere but not in Finder usually has something unusual about the container, not the image data.

A separate, much simpler cause catches people more often than the technical one: Finder's View Options panel (Cmd+J) has a Show Preview checkbox that must be ticked for that specific folder, and some users have reported that a corrupted .DS_Store file in a folder can leave this setting effectively stuck off. Reopen View Options for the affected folder, confirm Show Preview is checked, and if it already is, try toggling it off and back on.

If neither fixes it, nudge the thumbnail size slider down and back up (Cmd+J, drag the Icon Size slider) to force a rebuild, which several users on Adobe's own community forums report working for stubborn individual thumbnails. As a last resort, export the photo as JPEG from Preview; if the JPEG shows a thumbnail and the HEIC still doesn't, the HEIC file itself, not your Mac, is the problem.

RAW Files: Your Camera, Not Your Settings

Finder's RAW thumbnails come entirely from Apple's own RAW decoder, shipped as periodic Digital Camera RAW Compatibility updates, which is a completely separate codebase from Adobe Camera Raw. That's why the same RAW file can preview perfectly in Lightroom or Bridge while showing nothing in Finder, or the reverse. Before assuming a bug, check System Information (hold Option, Apple menu > System Information) under Software > Raw Support, which lists every camera model and RAW variant your current macOS version actually supports.

Being on that list isn't always enough. A case reported on Adobe's own community forum in October 2025 found a Fujifilm X-E5 listed as supported on macOS Tahoe 26.0.1, yet only its uncompressed RAF files generated Finder thumbnails; compressed RAF files from the same camera, same macOS version, showed only the generic RAW icon. The reporter's camera was set to the default lossless-compressed mode. If your camera supports both compressed and uncompressed RAW, switching to uncompressed is worth testing directly.

Separately, Canon CR3 (and some CR2) thumbnails started showing a black rectangle instead of the image in Finder and Quick Look for multiple users after the macOS Sequoia 15.4 and 15.4.1 updates, a regression documented in a long Apple Support Communities thread rather than a one-off. Manually resizing the Finder window brought the preview back for some people, though slowly, and a few reported that switching the display's color preset to Photography helped; several users reported the issue gone after updating to macOS 15.5 or 15.6, though that is an unconfirmed user report rather than an Apple release note. If you hit something similar, check for a pending macOS update before trying anything else.

PDF Documents: Generic Icon Instead of Page One

PDFs have two distinct failure modes, and they need different fixes. The first is purely cosmetic: a forum-reported case found a PDF showing only the generic file icon at Finder's default icon size, with the actual first-page thumbnail appearing once the icon size was increased with the slider under Cmd+J. If you're on a small icon size, try the largest setting before concluding anything is broken.

The second is specific to PDFs that went through Adobe Acrobat's optimization or "fast web view" processing, which can strip the embedded thumbnail image to shrink file size. Finder then has no pre-rendered image to show and falls back to the generic app icon. Opening the file once in Preview typically forces macOS to regenerate a thumbnail from the actual page content; if that doesn't stick, re-exporting the PDF without the optimization setting fixes it at the source.

If both of those come back clean and the cache reset above didn't help either, resetting NVRAM or PRAM has fixed stuck generic icons for some users according to reports referencing Apple's own NVRAM reset support article, though this is a broader, lower-probability fix worth trying only after the PDF-specific checks above.

Video Files: Works in the Folder, Fails in Search

Video thumbnails fail in a genuinely different pattern than photos or documents: a reported case found MP4 and MOV files on an external SSD showing full thumbnails when the folder was browsed directly, with the exact same files showing no preview at all inside Finder's own search results, while files on the internal drive behaved normally either way. That points at Spotlight's search index for the volume, not Quick Look or the video codec, since direct browsing and search draw thumbnails through different code paths.

If your symptom matches that pattern, exclude and then re-include the affected volume under System Settings > Siri & Spotlight > Spotlight Privacy to force a reindex, then search again once indexing finishes (the menu bar Spotlight icon shows a pulsing dot while it's working).

A second, less common pattern is iPhone-sourced .mov files imported with Photos set to Keep Originals rather than Automatic; some users report these specific files lacking thumbnails until the Photos transfer setting is changed. If you're dealing with iPhone video clips specifically and the fixes above don't apply, check Photos > Settings > General for that setting before anything else.