Para Tumbleweed execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/Tumbleweed/home:plater.repo
zypper refresh
zypper install GraphicsMagick
Para Factory execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/Factory/home:plater.repo
zypper refresh
zypper install GraphicsMagick
Para 16.0 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/16.0/home:plater.repo
zypper refresh
zypper install GraphicsMagick
Para 15.6 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:plater/15.6/home:plater.repo
zypper refresh
zypper install GraphicsMagick