Portrait shadow manipulation

• Published in: ACM transactions on graphics 2020-07, Vol.39 (4), p.78:1-78:14, Article 78
• Main Authors: Zhang, Xuaner (Cecilia), Barron, Jonathan T., Tsai, Yun-Ta, Pandey, Rohit, Zhang, Xiuming, Ng, Ren, Jacobs, David E.
• Format: Article
• Language: English
• Subjects: Computational photography; Computer graphics; Computing methodologies; Image manipulation
• ISSN: 0730-0301; 1557-7368
• DOI: 10.1145/3386569.3392390

Casually-taken portrait photographs often suffer from unflattering lighting and shadowing because of suboptimal conditions in the environment. Aesthetic qualities such as the position and softness of shadows and the lighting ratio between the bright and dark parts of the face are frequently determined by the constraints of the environment rather than by the photographer. Professionals address this issue by adding light shaping tools such as scrims, bounce cards, and flashes. In this paper, we present a computational approach that gives casual photographers some of this control, thereby allowing poorly-lit portraits to be relit post-capture in a realistic and easily-controllable way. Our approach relies on a pair of neural networks---one to remove foreign shadows cast by external objects, and another to soften facial shadows cast by the features of the subject and to add a synthetic fill light to improve the lighting ratio. To train our first network we construct a dataset of real-world portraits wherein synthetic foreign shadows are rendered onto the face, and we show that our network learns to remove those unwanted shadows. To train our second network we use a dataset of Light Stage scans of human subjects to construct input/output pairs of input images harshly lit by a small light source, and variably softened and fill-lit output images of each face. We propose a way to explicitly encode facial symmetry and show that our dataset and training procedure enable the model to generalize to images taken in the wild. Together, these networks enable the realistic and aesthetically pleasing enhancement of shadows and lights in real-world portrait images.1