% you can try different a and c until it looks right; quick test
% image(-log(flipud(rot90(J))+eps));axis('square');axis('xy')
% hold on
%
% testlightdark(a,c);

function returnsnothing(a,c)
f1=linspace(0,255,1000);
f2=lightdarkcoon(f1,4,a,c);

plot(f1,f2)

axis([0 255 0 255])
axis('square')