rx = 255
ry = 1023
b = 33


f(x)= ry * (b**(x/rx) - 1) / (b-1)

set xrange[0:rx]
set terminal png
set title sprintf("rx=%.1f, ry=%.1f, b=%.1f, f(%.1f)=%.1f, f(%.1f)=%.1f", rx, ry, b,0,f(0), rx, f(rx))
set output 'led_b.png'
plot f(x)