Read data from System objects in Matlab

I am using the Foreground Detection example in Matlab, using Gaussian Mixture Models, given in this link

http://in.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html

Part of the code where the foreground detection is done, is given below

        videoSource = vision.VideoFileReader('viptraffic.avi',...
        'ImageColorSpace','Intensity','VideoOutputDataType','uint8');

        detector = vision.ForegroundDetector(...
       'NumTrainingFrames', 5, ...
       'InitialVariance', 30*30);

The system object *detector* has the foreground mask. Simply put, How do I access this mask from the system object?

It is possible to use other methods of the class, which make use of the mask computed. But I am not able to find a way to get this mask out and use it for my own code/purpose.