My images are blurry and after searching around, I understand that the image sizes are defined somewhere in WooCommerce (maybe here: /includes/class-woocommerce.php).

I’ve also found this, relating to my question: https://woocommerce.github.io/code-reference/classes/WooCommerce.html#method_add_image_sizes , Not sure if it’s the right thing and I don’t understand what to do with it, or where to put it.