f(x,y) = y**4 - x**4 - 48*y**2 + 50*x**2 set xrange [-15:15]; set yrange [-15:15] set isosample 600,600 set view 0,0 set size square unset key; unset ztics; unset xtics; unset ytics; unset border; set cntrparam levels incremental -40,10,40 set contour base unset surface set terminal png size 900,720 set output 'diable.png' splot f(x,y) set output !mogrify -trim diable.png