set pm3d hidden3d 100
set style line 100 lt 3 lw 0
unset colorbox
set cbrange [-4:2]
set palette rgb 7,7,3
set size square
set view 60,80,1,1
f(x,y)=-x**3+3*x*y-y**3
set isosamples 30,30
set ticslevel 0
unset surface
set term png transparent xffffff
set out "nose.png"
splot [-3:3][-3:3] f(x,y)<-3 ? -3 : f(x,y)>1 ? 1: f(x,y) lt 2
!convert -geometry 50% -colors 512 nose.png nose_s.png
!display nose_s.png