RGL is looking to recruit a PhD student in the wider area of differentiable and inverse rendering / rendering systems / appearance modeling in the upcoming admissions cycle (deadline: December 15, 2019).
Are you excited about any of the following topics?
In addition to generating an image, a differentiable rendering algorithm propagates derivative information through the entire simulation (a bit like PyTorch/TensorFlow, but highly specialized to the physics of light). This enables fascinating and completely new uses of rendering algorithms to solve inverse problems. RGL is developing Mitsuba 2, a new rendering system that can be used to this end. Here are two recent RGL papers related to this topic:  .
Modern rendering systems are large and complex. They involve advanced physical effects (spectra, polarization, wave-optical interference), GPU and CPU implementations, differentiation, and a variety of different rendering techniques (Bidirectional Path Tracing, Metropolis Light Transport, Vertex Connection Merging, Gradient Domain methods, etc.). Dealing with all of this complexity using standard programming languages (e.g. C++) is an increasing challenge. I'd to rethink how they are built, including the underlying programming languages.
Material acquisition and modeling
Materials found in the real world are beautiful and often cannot be described well by simple models used in computer graphics. I am interested in measuring materials to understand their properties, and to use those insights to improve the models that are currently used. My group has access to one of the world's most advanced motorized gonio-photometers for acquiring their optical properties, which is a unique opportunity for work in this area. Here is a recent paper on this topic: 
EPFL offers a world-class, highly collaborative international research environment with competitive salaries and a beautiful setting on the shores of Lake Geneva. Applicants should have a 4-5 year bachelor's degree or a master's degree in computer science, mathematics, engineering, or related fields. PhD studies at EPFL's School of Computer and Communication Sciences are organized within a centralized PhD program named EDIC—applications to this program are due on December 15, and they are evaluated by a committee with faculty from different areas (hence, your application should be mostly understandable to a general CS audience). If you plan to apply, please drop me an email with your CV and I would be happy to schedule a Skype call with you to learn more about your background and interests.