Learning Inclusion Matching for Animation Paint Bucket Colorization
Authors: Yuekun Dai, Shangchen Zhou, Qinyue Li, Chongyi Li, Chen Change Loy

Colorizing line art is a pivotal task in the production of hand-drawn cel animation. This typically involves digital painters using a paint bucket tool to manually color each segment enclosed by lines based on RGB values predetermined by a color designer. This frame-by-frame process is both arduous and time-intensive. Current automated methods mainly focus on segment matching. This technique migrates colors from a reference to the target frame by aligning features within line-enclosed segments across frames. However issues like occlusion and wrinkles in animations often disrupt these direct correspondences leading to mismatches. In this work we introduce a new learning-based inclusion matching pipeline which directs the network to comprehend the inclusion relationships between segments rather than relying solely on direct visual correspondences. Our method features a two-stage pipeline that integrates a coarse color warping module with an inclusion matching module enabling more nuanced and accurate colorization. To facilitate the training of our network we also develope a unique dataset referred to as PaintBucket-Character. This dataset includes rendered line arts alongside their colorized counterparts featuring various 3D characters. Extensive experiments demonstrate the effectiveness and superiority of our method over existing techniques.