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Premise

OS: Ubuntu 20.04.2
DE: Gnome 3
gnome-shell --version: 3.36.7

In normal circumstances, I prefer not to re-generate thumbnails too often, in order to spare some lifespan for my SSD.

org.gnome.desktop.thumbnail-cache maximum-size: -1

org.gnome.desktop.thumbnail-cache maximum-age: 275

My thumbnails directory: ~/.cache/thumbnails/large/ contains around 37000 items amounting to 2.3GB.

The partition on which this directory (along with my user's home dir) is located has 16GB free space.

Recently I have installed Thunar to see thumbnails in bigger size than they are presented in Nautilus.

(I had installed Thunar in the standard recommended way for Gnome desktop: sudo apt install thunar)

Problems with tumbler

  1. Instead of the preferred 256px wide size, thumbnails are often generated and then presented in various ((much) smaller) sizes. (observed with .jpg images)
  2. Thumbnails can end up "unfinished", their bottom region remaining blocked in by a dark gray stripe (as if the processing of the bitmap data was abandoned mid-process). (observed with .png images)
  3. Sometimes landscape vs portrait orientation is not right.

To me all these seem to present themselves as some sort of race conditions. They happen quite a bit more frequently if the folder into which images are being saved at the moment is being open in Thunar.

My priority is solving the first item, the size issue.

To me it seems, the size-issue impacts only .jpg's and not .png's.

As I have found out, the thumbnails appearing in smaller sizes are also physically smaller than 256px in ~/.cache/thumbnails/large/.

Sometimes when saving / batch renaming files while the folder is open in Thunar, I can see a smaller-size thumbnail appearing for a split-second, and then getting replaced with the correct size. But this happens only to a few files, while the majority remains unchanged (too small).

Workarounds

What does not work:

  • refreshing the view in Thunar with ctrl+R
  • moving images across folders

What does work only sometimes / to some extent:

  • Right-clicking an image in Thunar and opening its "Properties" dialog sometimes — but altogether rarely — triggers re-generating the thumbnail in the correct size.
  • Deleting the most recent thumbnails in ~/.cache/thumbnails/large/ and then visiting the containing folder with Nautilus set to largest thumbnail view mode improves things.
    • (But still, less than 100% of the thumbnails will be the right size in Thunar, a few ends up being smaller, even then.)
  • Renaming image files.
    • This offers a clean start, but is still not guaranteed to end up right in 100% of the cases.

About Removing the contents of ~/.cache/thumbnails/

Removing the contents of the thumbnail cache would be attractive only if it would be guaranteed that the new set of thumbnails would be the right size.

But this does not seem to be guaranteed. Findings through partial deletions (e.g. the most recent few hundred thumbnails) suggest that the newly generated set would still suffer from the same size-issue. tumbler would need fixing first; then I would be ready to empty the thumbnails cache.

Basically I would like to see all new thumbnails getting generated at the right size; then I could go an retroactively fix the old thumbnails as well (by deleting them).

How to fix?

Can anything be achieved with some config, tweaking tumblerd somehow? Where is the corresponding config located?

Any other trick or workaround?

1 Answer 1

2

Solution TLDR;

If you find you have a [PixbufThumbnailer] plugin for tumbler, then you can disable [JPEGThumbnailer].

Apparent reason for the jpg thumbnail size-deviations:

These two thumbnailer plugins seem to be redundant, and even seem to compete with each other when generating thumbnails.

The hint is found in this documentation:

JPEG-thumbnailer

  Is that plugin still needed ? Pixbuf-thumbnailer as well supports jpeg. Is this plugin faster ?

Pixbuf-thumbnailer

  Supports [...] ani, bmp, GdkPixdata, gif, icns, ico, jpeg, png, pnm, qtif, svg, tga, tiff, wmf, xbm, xpm

How to fix:

Edit /etc/xdg/tumbler/tumbler.rc, and find the block:

# Jpeg thumbnailer (from exif data if possible)
[JPEGThumbnailer]
Disabled=false
Priority=3
Locations=
MaxFileSize=209715200

and set the value as follows: Disabled=true.

To let the change take effect, stop the tumblerd process in System Monitor (it will automatically restart on demand), or log out and log back in, or reboot.

Afterwards, new jpeg thumbnails will get generated

  • in the right size,
  • with the correct portrait vs landscape orientation,

albeit noticeably slower than before.

(Afterwards, only a subset of .pdf thumbnails will suffer from the smaller-than-configured size; I haven't found the fix for that yet.)


To fix all previously generated .jpg thumbnails as well, it's necessary to trigger the re-generating of all thumbnails. This can be achieved by emptying the thumbnail cache:

rm ~/.cache/thumbnails/ -rf

Afterwards, be patient: every image-containing directory you visit thereafter, will start re-generating the thumbnails within; not fun, but worth it.

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