function outImg = insertGabor (params, inImg)
% an example to use structure variable to organize input arguments
% written by YW, 2/2014

% Use meshgrid to define matrices x and y that range from -pi to pi;
[x,y] = meshgrid (linspace (-pi, pi, params.n));

if ~exist('inImg', 'var')
    inImg = zeros (params.n);
end

% Creat an oriented 'ramp' matrix as a linear combination of x and y. For
% example, when parms.orientation =0, cos=1 and sin=0 so ramp=x. When
% params. orientation is pi/2, then cos =0 and sin=1 so ramp=y.
ramp = cos (params.orientation)* (x-params.center(1))+sin(params.orientation)*(y-params.center(2));

% Sinusoidal carrier is a sinusoid on the matrix 'ramp'
sinusoid = params.contrast*sin(params.sf*ramp-params.phase);

% Gaussian envelope
Gaussian = exp(-((x-params.center(1)).^2+(y-params.center(2)).^2)/params.width^2);

% A gabor is the product of the sinusoid and the Gaussian
Gabor = sinusoid.*Gaussian;
outImg = inImg+Gabor;