f(x,y)=sin(x)+cos(y)+sin(x*cos(y)+y*sin(x))
g(x,y)=f(x,y)>0 ? 0: 1
set pm3d map
unset colorbox
set palette gray
set size square
unset key
unset xtics
unset ytics
set samples 512
set isosamples 512,512
set term png tiny crop
R=10
#
set out "g003.png"
splot [-R:R][-R:R] g(x,y)
#
set out "f003.png"
splot f(x,y)
#
set palette color
set out "f003c.png"
splot f(x,y)