Android: how to extract a System image

Usually to extract an image file of the Android /system partition we can use the simple Android Kitchen but if the System image is signed (System_signed) to extract it we have to use simg2img:

#!/sbin/sh
#
python simg2img.py system_signed tmp.img
sudo mount -t ext4 -o loop tmp.img extracted/

Sources: andwise, Hazou