Creating visually pleasing stylized ink paintings from 3D models is a challenge in robotic manipulation. We propose a semi-automatic framework that can extract expressive strokes from 3D models and draw them in oriental ink painting styles by using a robotic arm. The framework consists of a simulation stage and a robotic drawing stage. In the simulation stage, geometrical contours were automatically extracted from a certain viewpoint and a neural network was employed to create simplified contours. Then, expressive digital strokes were generated after interactive editing according to user's aesthetic understanding. In the robotic drawing stage, an optimization method was presented for drawing smooth and physically consistent strokes to the digital strokes, and two oriental ink painting styles termed as Noutan (shade) and Kasure (scratchiness) were applied to the strokes by robotic control of a brush's translation, dipping and scraping. Unlike existing methods that concentrate on generating paintings from 2D images, our framework has the advantage of rendering stylized ink paintings from 3D models by using a consumer-grade robotic arm. We evaluate the proposed framework by taking 3 standard models and a user-defined model as examples. The results show that our framework is able to draw visually pleasing oriental ink paintings with expressive strokes.

翻译：从3D模型生成具有视觉吸引力的风格化水墨画是机器人操作中的一项挑战。我们提出一种半自动框架，能够从3D模型中提取表现性笔触，并通过机械臂以东方水墨风格进行绘制。该框架包含仿真阶段与机器人绘制阶段。在仿真阶段，从特定视角自动提取几何轮廓，并采用神经网络生成简化轮廓；随后根据用户的审美理解进行交互式编辑，生成富有表现力的数字笔触。在机器人绘制阶段，提出一种优化方法以绘制平滑且物理一致的数字笔触对应线条，并通过机械臂控制毛笔的平移、蘸墨与刮擦操作，实现两种东方水墨风格——浓淡（阴影）与枯涩（涩感）。不同于现有聚焦于从2D图像生成绘画的方法，本框架的优势在于能够通过消费级机械臂，从3D模型渲染出风格化水墨画。我们以3个标准模型与1个用户自定义模型为例进行框架评估，结果表明该框架能够绘制出笔触表现力强、视觉悦目的东方水墨画。