KDE PLasma 5.13 now includes quite similar feature. Though it is not automatic, like this script, yet it is stock, and not as performance hungry as this realisation. Use it at your own risk (as always)
This script automatically detects when you change wallpaper in KDE Plasma, blurs it, and sets it to your lockscreen and SDDM.
You will need inotify-tools and imagemagick packages. Arch linux users can install it via pacman -S inotify-tools imagemagick. Other distros may include it by default. If not, check your distro wiki on how to install them.
Also you will need dbus, and the system should be installed on a filesystem with ACL.
$ git clone https://github.com/andreyorst/kde_wallpaper_blur.git ~/.kde_wallpaper_blur
$ cd ~/.kde_wallpaper_blur
$ ./setup.sh # this will ask for password, because there are some manipulations with SDDM files, wich requires root accessInstallation script will create image called .bg.png in your $HOME dir, and put a symlink to it into your current sddm theme folder. Then the blur script will be set to autostart, and started for current session.
No further manipulations should be needed, but if you run into some kind of trouble, please open issue with step by step guide how to reproduce it.
Installation script will create backup files called *.prewpblur in various places. Check out script output.
Multi-monitor systems: Please note that while different wallpapers can be set for different screens, only one background can be set for the lockscreen and SDDM. Therefore, this script will only use the wallpaper from your Primary Display.
To uninstall script simply run:
$ cd ~/.kde_wallpaper_blur
$ ./uninstall.shOr, if you choosen different path in installation section, execute script directly form there.
Special thanks to @agura-lex, for his patience and bash guidance, and @kennethso168 for implementing activity detection, and lots of improvements.