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For a webshop running on WooCommerce, I changed the default thumbnail size in WC > settings > products > display to:

  • Catalog Images: 247x247px
  • Single Product Image: 510x510px
  • Product Thumbnails: 130x130px
  • Hard Crop selected.

At first this went fine, new thumbs were regenerated and loaded via srcset on the webpages. However, because this configuration caused unsharp images on some screen resolutions, I decided to double thumbnail sizes (resolution 2X).

Nothing happened at this time, so I tried a lot of things to solve this issue: just keep trying to run "Regenerate thumbnails" on all files, run on select files, tried the "Force regenerate thumbnails" plugin, tried "Thumbnail Cleaner" plugin, added a custom function but all to no avail:

Renerate thumbnails shows a message like

"product-image-xxx" (ID XXXX) was successfully resized in 0.840 seconds.

but when I look in my FTP media folder, no new files are created. I remember from the time this plugin worked fine, it took a lot longer to create the desired thumbnails. I also tried disabling all thumbnail plugins except Regenerate thumbnails and emptying functions.php: no effect.

What is going wrong here? Running latest version of WP, WooCommerce and Regenerate thumbnails.

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The solution for this problem was rather strange. I hired a developer who helped me solve this:

  • increased memory limit in config.php (not sure if this was causing the problem since it didn't look like a time-out or anything)
  • in the file regenerate-thumbnail.php the line wp_update_attachment_metadata( $image->ID, $metadata ); was commented. I'm sure I did not do this myself, but I tried a lot of plugins to solve the problem; maybe one commented this?

To further enhance the performance, it's possible to generate thumbnails twice, e.g. for 1X and 2X displays. I'm not completely sure, but as far as I understand, in my case this will lead to generation of the following thumbails:

  • Catalog Images: 247x247px AND 494x494px
  • Single Product Image: 510x510px AND 1020x1020px
  • Product Thumbnails: 130x130px AND 260x260px

Your browser then will use srcset to check which files are available and by that choosing the best variant to display.

Hope this helps someone else as well.

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