f(x,y)=sin((x-y)/2)*sin((x+y)/2)*sin(x*cos(y)+y*sin(x))
g(x,y)=f(x,y) > 0 ? 1: 0
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 xrange[-R:R]
set yrange[-R:R]
#
set out "g009.png"
splot g(x,y)
#
set out "f009.png"
splot f(x,y)
#
set palette color
set out "f009c.png"
splot f(x,y)