# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'rgbalpha.2.png'
set border 31 front linetype -1 linecolor rgb "gold"  linewidth 1.000
set key title "Plot style rgbalpha" textcolor rgb "gold" 
set key at screen 0.75, 0.75, 0 left bottom vertical Left noreverse enhanced autotitles nobox
set key noinvert samplen 1 spacing 1 width -7 height 0 
set object  1 rect from screen 0, 0, 0 to screen 1, 1, 0
set object  1 behind lw 1.0 fc  rgb "grey10"  fillstyle   solid 1.00 noborder
set samples 128, 128
set size ratio 0.95 1,1
set style data lines
set xrange [ 0.00000 : 128.000 ] noreverse nowriteback
set yrange [ 0.00000 : 128.000 ] noreverse nowriteback
set lmargin at screen 0.1
set bmargin at screen 0.1
set tmargin at screen 0.9
focus(x,y) = ((column(0)-x)**2 + (column(-1)-(127-y))**2) > 400 ? 0 : 255
GPFUN_focus = "focus(x,y) = ((column(0)-x)**2 + (column(-1)-(127-y))**2) > 400 ? 0 : 255"
plot 100.*(.4+sin(x/5.)/(x/5.)) lw 5 title 'solid line',      'lena.rgb' binary array=(128,128) format="%uchar" flipy using 1:2:3:(focus(70,50))                 with rgbalpha title "Lena with circular mask"