swt.jpg is black

[SB2020-eye]

Hi. Using the example pic found in the script ([file_url = 'http://upload.wikimedia.org/wikipedia/commons/0/0b/ReceiptSwiss.jpg']), my result (swt.jpg) is all black.

Can someone help me understand how to achieve intended results? (Or else point to a working example of python swt?)

Thank you.