Dear Fellow Scholars, this is Two Minute Papers with Dr. Károly Zsolnai-Fehér.
I have been yearning for a light transport paper, and goodness, was I ecstatic when reading
this one.
And by the end of the video, I hope you will be too.
And now, we only have to go through just about 30 years of light transport research.
As some of you know, if we immerse ourselves into the art of light transport simulations,
we can use our computer to simulate millions and millions of light rays, and calculate
how they get absorbed or scattered off of our objects in a virtual scene.
Initially, we start out with a really noisy image, and as we add more rays, the image
gets clearer and clearer over time.
The time it takes for these images to clean up depends on the complexity of the geometry
and our material models, but it typically takes a while.
This microplanet scene mostly contains vegetation, which are matte objects, these we also refer
to as diffuse materials, these typically converge very quickly.
As you see, we get meaningful progress on the entirety of the image within the first
two minutes of the rendering process.
And remember, in light transport simulations, noise is public enemy number one.
This used a technique called path tracing.
Let’s refer to it as the okay technique.
And now, let’s try to use path tracing, this okay technique to render this torus in
a glass enclosure.
This is the first two minutes of the rendering process, and it does not look anything like
the previous scene.
The previous one was looking pretty smooth after two minutes, whereas here, you see,
this is indeed looking grim.
We have lots of these fireflies, which will take us up to a few days of computation time
to clean up, even if we have a modern, powerful machine.
So, why did this happen?
The reason for this is that there are tricky cases for specular light transport that take
many-many millions, if not billions of light rays to compute properly.
Specular here means mirror-like materials, those can get tricky, and this torus that
has been enclosed in there is also not doing too well.
So this was path tracing, the okay technique.
Now let’s try a better technique called Metropolis Light Transport!
This method is the result of a decade of research and is much better in dealing with difficult
scenes.
This particular variant is a proud Hungarian algorithm by a scientist called Csaba Kelemen
and his colleagues at the Technical University of Budapest.
For instance, here is a snippet of our earlier paper on a similarly challenging scene.
This is how the okay path tracer did, and in the same amount of time, this is what Metropolis
Light Transport, the better technique could do!
This was a lot more efficient, so let’s see how it does with the torus.
Now that’s unexpected!
This is indeed a notoriously difficult scene to render, even for Metropolis Light Transport,
the better technique.
As you see, the reflected light patterns that we also refer to as caustics on the floor
are much cleaner, but the torus is still not giving up.
Let’s jump another 15 years of light transport research, and use a technique that goes by
the name Manifold Exploration.
Let’s call this the best technique.
Wow.
Look at how beautifully it improves the image, it is not only much cleaner, but also converges
much more gracefully.
It doesn’t go from a noisy image to a slightly less noisy image, but almost immediately gives
us a solid baseline, and new, cleaned up light paths appear over time.
This technique is from 2012, and it truly is mind boggling how good it is.
This technique is so difficult to understand and implement, that to the best of my knowledge,
the number of people who can and have implemented it properly is exactly one.
And that one person is Wenzel Jakob, one of the best minds in the game, and believe it
or not, he wrote this method as a PhD student in light transport research.
And today, as a professor at EPFL Switzerland, he and his colleagues set out to create a
technique that is as good as manifold exploration, the best technique, but is much simpler.
Well, good luck with that, I thought when skimming through the paper.
Let’s see how it did.
For instance, we have some caustics at the bottom of a pool of water, as expected, lots
of firefly noise with the okay path tracer, and now, hold on to your papers, and here
is the new technique.
Just look at that!
It can do so much better in the same amount of time!
Let’s also have a look at this scene with lots and lots of specular microgeometry, or
in other words, glints.
This is also a nightmare to render.
With the okay path tracer, we have lots of flickering from one frame to the next, and
here you see the result with the new technique.
Perfect.
So it is indeed possible to take the best technique, manifold exploration, and reimagine
it in a way that ordinary humans can also implement.
Huge congratulations to the authors on this work, that I think, is a crown achievement
in light transport research.
And that’s why I was ecstatic when I first read through this incredible paper.
Make sure to have a look at the paper and you will see how they borrowed a nice little
trick from a recent work in nuclear physics to tackle this problem.
The presentation of the paper and the talk video with the details is also brilliant and
I urge you to have a look at it in the video description.
This whole thing got me so excited I was barely able to fall asleep for several days now.
What a time to be alive!
Now, while we look through some more results from this paper, if you feel a little stranded
at home and are thinking that this light transport thing is pretty cool, and you would like to
learn more about it, I held a Master-level course on this topic at the Technical University
of Vienna.
Since I was always teaching it to a handful of motivated students, I thought that the
teachings shouldn’t only be available for the privileged few who can afford a college
education, but the teachings should be available for everyone.
Free education for everyone, that’s what I want.
So, the course is available free of charge for everyone, no strings attached, so make
sure to click the link in the video description to get started.
We write a full light simulation program from scratch there, and learn about physics, the
world around us, and more.
Also, note that my former PhD advisor, Michael Wimmer is looking to hire a postdoctoral researcher
in this area, which is an amazing opportunity to push this field forward.
The link is available in the video description.
Thanks for watching and for your generous support, and I'll see you next time!