As brought up at the mailinglist, this code ates up much memory:

spectrumArray = np.random.randint(0,255, (2**20,2**12)).astype(np.uint8)

It has also crossed my mind that np.random.randint and np.random.rand could use an extra 'dtype' keyword. It didn't look easy to implement though.

See this thread on the mailinglist: [Numpy-discussion] array of random numbers fails to construct