Tong, Z., X. Chen, B. Ni, and X. Wang. “Sketch Generation With Drawing Process Guided by Vector Flow and Grayscale”. Proceedings of the AAAI Conference on Artificial Intelligence, vol. 35, no. 1, May 2021, pp. 609-16, https://ojs.aaai.org/index.php/AAAI/article/view/16140.