to creative a low pass filter for The chrominance spatial frequency response MTF i am having some problem...i am giving the code below...but i m getting some ripples.....what is the solution???

function tintin=tintin(s,d) [f1,f2] = freqspace(s,'meshgrid'); Hd = ones(size(f1)); r = sqrt(f1.^2 + f2.^2); % th=atan(f2./f1); % s_th=0.15*cos(th.*4)+0.85; % rs=r./s_th; % rd=rs.*(d*pi/180); a=131.6; b=0.3188; c=0.525; d=3.91; for i=1:s for j=1:s % Hd(i,j)=2.6*(0.0192+rd(i,j)*0.114)*exp(-(0.114*rd(i,j))^1.1); % Hd(i,j)=exp(-rd(i,j)/(0.525*log(11)+3.91)); Hd(i,j)=100*(-0.419*sprt(i^2+j^2));%Pritha project end end Hd(((s-1)/2)+1,((s-1)/2)+1)=1; fc=fsamp2(Hd); freqz2(fc); tintin=fc;