Computer scientists at the University of California in San Diego (UCSD) have developed a fog and smoke machine for computer graphics which dramatically cuts computing costs for generating bright images. They've used 'photon mapping' algorithms, a subset of the more computationally intensive ray tracing algorithms -- and with better results. This could lead to better computer graphics for movies and video games. Now, the researchers are adapting their algorithms to render other materials, such as skin, milk and plants which behave more or less like fog or smoke. But read more...
As you can see on the left, "the light piercing the fog in the top image is smooth, realistic and computationally light-weight thanks to a new method for gathering light for computer graphics via photon mapping. In the bottom image, the very same scene was generated using the conventional light gathering approach. Both images consumed the same computational resources." (Credit: UCSD)
This research project has been led by Wojciech Jarosz, a Ph.D student at UCSD and a member of the UCSD Computer Graphics Laboratory. He works about rendering algorithms under the supervision of two UCSD computer science professors, Henrik Wann Jensen and Matthias Zwicker.
Here is a straight comment from Jarosz about the 'photon mapping' algorithm he used. "We took an algorithm that is already great and made it more efficient."
Here is a longer description of what the researchers have achieved. "Much of the richness in images created with photon mapping algorithms comes from precise accounting for the amount of light is in a scene and where that light is. Photon mapping algorithms provide a way to follow the light around the scene, as it bounces off various objects and lands on other objects. Photon mapping can also determine how light will interact with fog, smoke or other “participating media” that absorb, reflect and scatter some portion of the light – a task that has been traditionally quite computationally costly to perform because it requires sampling the light at many locations in order to make sure that nearly all the light is accounted for."
And as underlines Jarosz, "Instead of computing the light at thousands of discrete points along the ray between the camera and the object, which is the conventional approach, we compute the lighting along the whole length of the ray all at once."
This research work will be presented at the Eurographics 2008 held in Hersonissos, Crete, Greece, between April 14 and 18, 2008. The technical paper, "The Beam Radiance Estimate for Volumetric Photon Mapping,"will be included in a Computer Graphics Forum (Volume 27, Number 2, April 2008) containing the proceedings of the conference.
Here is the abstract of this technical paper (PDF format, 10 pages, 15.8 MB). "We present a new method for efficiently simulating the scattering of light within participating media. Using a theoretical reformulation of volumetric photon mapping, we develop a novel photon gathering technique for participating media. Traditional volumetric photon mapping samples the in-scattered radiance at numerous points along the length of a single ray by performing costly range queries within the photon map. Our technique replaces these multiple point-queries with a single beam-query, which explicitly gathers all photons along the length of an entire ray. These photons are used to estimate the accumulated in-scattered radiance arriving from a particular direction and need to be gathered only once per ray. Our method handles both fixed and adaptive kernels, is faster than regular volumetric photon mapping, and produces images with less noise."
Earlier results have been mentioned in a previous UCSD news release, "Render Smoke and Fog without being a Computation Hog" (August 9, 2007). For more information, you can read a paper presented during SIGGRAPH 2007, "Radiance Caching for Participating Media" (PDF format, 2.94 MB).
I want to leave the last words of this post to Jarosz, who "does not expect movies and video games to strictly follow the laws of nature. 'In live action movies, the lighting is incredibly controlled. If a character walks into a shadow, they will add light to the face even if you would never get that kind of light in a real shadow. The composition on the screen must tell the story and not distract the viewer. Realism doesn't always matter. It’s the movies.'"
Sources: UCSD Jacobs School of Engineering, April 15, 2008; and various websites
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