Белоус, Н. В., В. П. Власенко, and А. И. Красов. “Aligning the Background Brightness of Images of Text Characters Using a High-Pass Filter”. Bulletin of V.N. Karazin Kharkiv National University, Series «Mathematical Modeling. Information Technology. Automated Control Systems», Vol. 37, no. 1, Jan. 2018, pp. 5-19, https://periodicals.karazin.ua/mia/article/view/10512.