Figure from the paper illustrating how light moves through a scene at each time step.

Figure from the paper illustrating how light moves through a scene at each time step.

A new study co-authored by Visual Computing Lab Director Wojciech Jarosz builds on his previous work simulating how light is scattered, refracted, and reflected. Rather than assume the speed of light is infinite, as one usually would in computer graphics, this work incorporates the true speed of light in order to visualize how light bounces around a scene filled with particles and surfaces.

Full details of the study can be found here.

This work, along with the previous work it was built upon, was conducted in collaboration with researchers at the University of Zaragoza. It was published in the journal Computer Graphics Forum in March.

For a teaser of what can be accomplished with the new technique, this accompanying video illustrates light moving through virtual scenes:

New photographic techniques developed in the past decade have been able to capture light on the order of picoseconds, informing research on how light moves through space, seeing around corners, and discovering material properties. Being able to simulate the movement of light with extreme accuracy could provide benchmarks, forward models for optimization, or training sets for machine learning in the real world.

This paper proposes an improved method called progressive transient photon beams for visualizing the movement of light through a volume filled with tiny, light-scattering particles. Real-world materials that resemble these particle volumes include fog, clouds, ocean water, marble, and skin.

Although there are existing rendering algorithms that mimic the natural behavior of light, where photons are emitted from a light source and bounce around a scene, these algorithms operate by following each photon from start to finish. The authors of this study, however, tackled the more difficult problem of finding where all the photons are at a single point in time.

As such, the technique proposed in this paper involved extensive reworking of the traditional rendering equation, an integral summing the contribution of all light arriving at a point in space, to include time.

The team also leveraged previous work on simulating light in a scattering volume called progressive photon beams, which involves shooting many short beams of light into the material in order to estimate the total presence of light in every area.

Lastly, the authors analyzed the convergence rate of their new technique, which is crucial due to the very long rendering times of scenes with scattering materials. They discovered a way to tune the parameters for their progressive transient photon beams in order to achieve an optimal convergence rate.

Using their technique, they were able to visualize what an instantaneous pulse or continuous stream of light might look like charging through a scene, as demonstrated in the supplemental video.

This exciting new study opens the door a little wider toward using extremely realistic computer-generated images to enhance our knowledge of real-world phenomena.

Credit for this work goes to Julio Marco (Universidad de Zaragoza), Ibón Guillén (Universidad de Zaragoza), Wojciech Jarosz (Dartmouth College), Diego Gutierrez (Universidad de Zaragoza), and Adrian Jarabo (Universidad de Zaragoza).