Hello, I have confusing with generation gabor filter bank,

since I found in many codes on the internet they use different formula and I do not know how can determine the value of x,y in the filter bank of Gabor, please help. I have used the code below from wikibdia site for image feature detection,I do not know is it correct? his co can any body explain generation of x and y values in this code, is it fixed formula in gabor bank filter or what? function gb=gabor_fn(sigma,theta,lambda,psi,gamma)

sigma_x = sigma; sigma_y = sigma/gamma;

% Bounding box nstds = 3; xmax = max(abs(nstds*sigma_x*cos(theta)),abs(nstds*sigma_y*sin(theta))); xmax = ceil(max(1,xmax)); ymax = max(abs(nstds*sigma_x*sin(theta)),abs(nstds*sigma_y*cos(theta))); ymax = ceil(max(1,ymax)); xmin = -xmax; ymin = -ymax; [x,y] = meshgrid(xmin:xmax,ymin:ymax);

% Rotation x_theta=x*cos(theta)+y*sin(theta); y_theta=-x*sin(theta)+y*cos(theta);

gb= exp(-0.5*(x_theta.^2/sigma_x^2+y_theta.^2/sigma_y^2)).*cos(2*pi/lambda*x_theta+psi);

what does 'nstds = 3;' here mean??? please help thank you all.