Your have installed http://gegl.org/ ?
gegl -p -o output.png -x "<gegl><node operation='gegl:c2g'><params><param name='radius'>1800</param><param name='samples'>16</param><param name='iterations'>16</param></params></node><node operation='gegl:load'><params><param name='path'>input.png</param></params></node></gegl>"