%loop through image and apply mask randomly
for i = 1 : step.h : input.h - window.h-step.h
    for j = 1 : step.w : input.w - window.w-step.w
        
        % extract part of the image
        window.current = input.image(i : i + window.h - 1, j : j + window.w - 1, :);
        
        % apply mask randomly
        color = round(rand(1) * 5) + 1;
        mask.current = mask.(fn{color});
        
        % apply
        
        
    end
end