Pixar's Lightspeed Brings New Light to Monsters University

No, literally. Pixar's lighting/rendering systems were completely redone for their new film Monsters University. In my correspondence with Chris Horne, who studied Visualization at A&M and works Pixar's Lightspeed, he mentioned his work on MU:

I was on MU from May 2012 until April 2013 -- so yeah I worked on it for a *very very* long time as far as the lighting department is concerned. When I joined it was only leads + 1 shot lighter and me. It was a blast to work on because we completely rewrote our lighting system to be a raytraced/GI system -- and since I was on early I got to test the boundaries of it and figure out how we should light the show from a technical aspect. We really explored the lighting system - and I feel like a significant amount of work we did back then is going to live on in the way we light shows with this new technology. It was really unnerving and weird though to run into something new, ask some really smart people what the hell is going on, and hear back "We have no idea. It's all new. Good luck!" P.S. - the film is fully done and in the can as of this week (including credits, stereo, and all their international permutations, and the audio related to all of those). Creative production here finished maybe the 2nd week of April?

I was surprised that Pixar was just now using all ray tracing in their system. A few emails later I asked him if audiences will notice the difference in lighting:

There's a huge difference in MU compared to past films. Even people that don't know anything about our tech change going in walk out going "HOLY CRAP!"....but they have a hard time putting their finger on why it looks so awesome. Personally I see a huge difference between MU and Brave - there's more shaping, more little splashes of color, and everything feels a little bit more dynamic and pulled together. This is particularly evident in the toxic urchins sequence - where every single urchin is a light source. We couldn't have done that sequence in the past with our old technology. 

Historically we don't use raytracing. It wasn't until Cars that we actually supported raytracing (and even then it was a haphazard and mostly broken support). We really only used it for highly reflective smooth curved surfaces that absolutely needed to be truly reflected and not faked. We fake almost everything - mirrors, wet surfaces, eyes, shiny props like belt buckles/spoons/swords/etc. We obviously can't get away with that on Lightning McQueen - so we would cache out the scene into a brickmap (essentially a kd-tree with shading attached to the voxels) and fire rays against that (so even then....we aren't doing traditional raytracing). For shadows - we would sometimes use raytracing when we needed particularly awesome looking contact shadows. The same shadow would ramp off to using a shadowmap to help lower the expense. 

So our Director of Photography went to a studio that is so clearly raytracing averse and essentially said "We're raytracing everything. True reflection and refraction in the eyes reflecting actual SCENE GEOMETRY and not a brickmap. Yep - we're refracting through the cornea onto the sclera and iris. Oh and all your shadows are raytraced now - no more shadowmaps. Nope. None. Yes I know you like them but no. And global illumination! We're doing that now. By default. Everywhere. Oh and I almost forgot - all reflective surfaces will do real true reflection....and deciding what's reflective will be a shading decision instead of a lighting one. Yes you heard me right. Now get to work" It was extremely controversial, but it made a huge impact and really was one of the true success stories of the film. And now I'm working on that.

If you're advanced enough to understand the tech jargon above, good for you. For the uninitiated, ray tracing is a relatively advanced CG lighting technique which virtually simulates actual rays of light and all their interactions with the objects in your environment. In technical terms, Global Illumination lighting is like super hard core ray tracing. Both techniques use up a lot of memory. A more comprehensive explanation can be found here.

I was surprised that ray tracing in Pixar was historically a clunky, haphazard process. I always thought of it as this smooth, polished machine like something you would see at an Apple store. It's cool to see Pixar making history and advancing themselves over the past couple of years, I mean you can already see the difference in the images above.

Follow Chris on Twitter: @distastee
And follow me on Twitter: @masonsmtx