I'm on Ubuntu 20.04 with Xfce desktop environment and the thumbnails of my .heic files are not showing. I can see the pictures in Image viewer, but not on the thumbnails and I'm bothered by that.
I have already tried what's suggested here : heif-gdk-pixbuf, heif-thumbnailer and libheif1 are correctly installed and no error pop in the terminal. However, no thumbnail is showing. How can I fix this?
See How to view .HEIC photos from iPhone IOS 11+ on Ubuntu? to get info on what software you need to install to view .HEIC images.
You're using a File Manager in Xfce that won't display these thumbnails.
Use Nautilus File Manager and you'll see the thumbnails.
Xfce by default has file manager Thunar and thumbnail generator service Tumbler. Tumbler is extensible, by adding thumbnailers, thumbnails for more types of files can be generated and shown in Thunar, one can also add one's own to generate thumbnails for all kinds of files as one desire.
Installing heif-thumbnailer adds the file /usr/share/thumbnailers/heif.thumbnailer, with image/heif; listed after MimeType=. This should be picked up by Tumbler automatically. This can be confirmed by running the program /usr/lib/x86_64-linux-gnu/tumbler-1/tumblerd manually, it should contain a line like
Registered thumbnailer heif-thumbnailer -s %s %i %o
Try having only heif-thumbnailer installed but not heif-gdk-pixbuf. It may just work.
This may sound strange but installing heif-gdk-pixbuf may not add heif support to thumbnail generators like Tumbler. Further, possibly because of bugs, it may even prevent heif-thumbnailer from working with Tumbler.
Theoretically, Tumbler, with the included plugin Pixbuf-thumbnailer, should be able to generate thumbnails for the plurality of file types gdk-pixbuf supports.
gdk-pixbuf is modular and can be extended by installing additional loaders, such as heif-gdk-pixbuf, which adds heif support. Using the program gdk-pixbuf-thumbnailer from the package libgdk-pixbuf2.0-bin, one can verify that given an heif image, a thumbnail can be generated.
However, by inspecting the file /usr/share/thumbnailers/gdk-pixbuf-thumbnailer.thumbnailer, one finds that heif doesn't seem to be listed among supported MimeTypes. So thumbnailers like Tumbler may fail to recognize the capabilities added to gdk-pixbuf.
And when I have both heif-thumbnailer and heif-gdk-pixbuf installed, heif thumbnailing stops working. Through trial and error, I seem to find something wrong with JPEGThumbnailer that comes with tumbler. Although it should be only for JPEG files, installed libraries may be interacting in unexpected ways. One can see from /etc/xdg/tumbler/tumbler.rc that it has a high priority: Priority=3. So if you need heif-gdk-pixbuf for purposes other than thumbnailing, you may try to avoid the JPEGThumbnailer of tumbler by overwriting its priority in the file ~/.config/tumbler/tumbler.rc with:
[JPEGThumbnailer]
Priority=1
or you can just disable it, it's not the only provider of JPEG thumbnails:
Disabled=true
Upcoming versions will try to keep trying multiple thumbnailers, so the situation will hopefully get better: https://gitlab.xfce.org/xfce/tumbler/-/issues/50
