CGI hackers discover secret of rainbows

Computer graphics professionals, seeking out more realistic simulations for natural phenomena for video games and movies, gain a striking new insight into the how rare types of rainbows work.

UC San Diego Jacobs School of Engineering

If you thought animating human motion for a video game or feature movie was hard, try rainbows.

In the search for better animation techniques for video games and movies, computer graphics researchers at the University of San Diego have gained insight into the physics of rainbows. Their discovery could lead to more realistic depictions of rare types of rainbows, such as twinned rainbows, and other natural phenomena.

The conditions for the appearance of a rainbow are well understood: light passing through water droplets in the air causes the light to reflect and refract within the water. The reflecting light fans out as it leaves the water droplets in such a way that the full spectrum of colors is visible.

When trying to simulate a rainbow in software, the researchers assumed that raindrops are spherical. But in pursuing a more accurate model, they learned that larger raindrops flatten at the bottom, causing a slightly different physical conditions.

By gaining a more realistic understanding of the mechanisms at play, researchers have been able to simulate different types rainbows, including supernumerary rainbows where several faint rainbows form on the inside of the primary arc.

"This goes beyond computer graphics," a said computer science professor Henrik WannJensen, who earned an Academy Award in 2004 for work in simulating realistic skin in animated characters "We now have an almost complete picture of how rainbows form."

Jensen and other researchers are scheduled to publish their findings this month in ACM Transactions on Graphics. "You usually don't get the opportunity to study such beautiful phenomena while working on your PhD thesis," said Iman Sadeghi, who is now a software engineer in the graphics division of Google. "There is a lot more to rainbows than meets the eye."

 

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