Recently a question that came to my mind was that How are Physically Based Rendering Techniques researched and developed? Do people just use current equations by physicists or do they create their own? Hopefully I've explained my question correctly.
How are Physically Based Rendering Methods Researched?
rendering;physically based;pbr
I think you need to split your question into real-time and offline PBR research.For real-time PBR it's mostly about finding fast approximations for path traced equivalent. For example we know how to implement area lighting with contact hardening shadows with a simple MC integrator, but finding fast approximation for this is a complex task requiring strong background in mathematics and rendering algorithms/data structures.For offline PBR research I think it's partly about understanding optics and limitations of current PBR algorithms and where the two diverges in a significant & meaningful way in the worlds we try to simulate. For example we know that the microfacet model is an approximations of the more complex way light interacts with surfaces, but are there important situations where this approximation fails in a significant way that we would need a better model?Also even in offline rendering the performance is an issue, and all kinds of clever mathematical techniques needs to be developed and employed to speed up computations. For example calculating multiple scattering in participating media with brute force path tracing is extremely time consuming and clever techniques are needed to make this computation feasible for movies for example. Or techniques such as importance sampling is developed to reduce the computation in an unbiased way.For both real-time and offline PBR research you need sufficient background information in the domain of research and good mathematical/algorithmic toolbox to be able to make any meaningful contribution to the research.