Another possibility to have other outlines (experimentation).
-tones[-1] 3
-isophotes[-1,-2] 3
-blend[-1,-2] alpha
-blend[-1,-2] alpha
-mul[-1] 255
-isophotes[-1] 3
{w},{h},1,4
-repeat {{{w}+{h}}/1.5} # delete points
-line[-2] 50%,50%,{u(100)}%,{u(100)}%,1,0,0,0,0
-done
-repeat {{{w}+{h}}/2} # points on outlines
-line[-1] {u(100)}%,{u(100)}%,{u(100)}%,{u(100)}%,1,255,255,255,255
-done
-repeat {{{w}+{h}}/5} # points outside the outlines
-point {u(100)}%,{u(100)}%,0,1,255,255,255,255
-done
-and[-1,-2]
-dilate_circ[-1] 3
-c[-1] 0,255
-to_rgb[-1]
