What's $mask in file_scan_directory() to find all png files? I try to find all png files in a directory inside my module using this code with no success:

$banks = file_scan_directory(drupal_get_path('module', 'order').'/images/gateways', '/^.*\png$/');


What mask should I used for getting all png files?
The following mask should work for you:

'/.*\.png$/'