function S = stim_images2matrix(filemask)
%This function loads a set of images as a 3D matrix. Color images are
%converted to grayscale when loaded, so the resulting matrix is always 3D
%with size X x Y x Z, where:
%   X is the size of the images along the X axis
%   Y is the size of the images along the Y axis
%   Z is the number of images
%
%   all images are assumed to be the same size (though they do not have to
%   be the same file format or number of bits per pixel

    files = dir(filemask);

    %figure out the file size
    I = imread([files(1).folder '/' files(1).name]);
    X = size(I, 1);
    Y = size(I, 2);
    Z = length(files);

    S = zeros(X, Y, Z, 'uint8');

    h = waitbar(0, ['Loading ' num2str(Z) ' images...']);
    for i = 1:Z    
        I = rgb2gray(imread([files(1).folder '/' files(1).name]));
        S(:, :, i) = I;
        waitbar(i/Z, h);
    end
    close(h);
end