Shigueo Nomura Keiji Yamanaka Takayuki Shiose Hiroshi Kawakami Osamu Katai Morphological preprocessing method to thresholding degraded word images. 729-744 2009 30 Pattern Recognition Letters 8 http://dx.doi.org/10.1016/j.patrec.2009.03.008 db/journals/prl/prl30.html#NomuraYSKK09