亲爱的学者们 这里是Károly Zsolnai-Fehér带来的两分钟论文
Dear Fellow Scholars, this is Two Minute Papers with Károly Zsolnai-Fehér.
Creating a photorealistic image with fur and hair is hard.
It is typically done by using light simulation programs where we use the laws of physics
to simulate the path of millions and millions of light rays as they bounce off of different
objects in a scene.
This typically takes from minutes to hours if we’re lucky.
然而 一些材料的存在 比如皮毛和毛发使得问题更加
However, in the presence of materials like hair and fur, this problem becomes even more
difficult, because fur fibers have inner scattering media.
This means that we not only have to bounce these rays off of the surface of objects,
but also have to simulate how light is transmitted between these inner layers.
首先 从一幅有噪声的图像开始 当我们在模拟中计算的光线数量越多
And initially, we start out with a noisy image, and this noise gets slowly eliminated as we
compute more and more rays for the simulation.
Spp means samples per pixel,
which is the number of rays we compute for each pixel in our image.
And you can see that with previous techniques, using 256 samples per pixel leads to a very
noisy image and we need to spend significantly more time to obtain a clear, converged image.
And this new technique enables us to get the most out of our samples,
and if we render an image with 256 spp,
we get a roughly equivalent quality to a previous technique
using around six times as many samples.
If we had a film studio and someone walked up on us and said that we can render the next
Guardians of The Galaxy film six times cheaper, we’d surely be all over it.
This would save us millions of dollars.
The main selling point is that this work introduces a multi-scale model for rendering hair and fur.
This means that it computes near and far-field scattering separately.
The far-field scattering model contains simplifications, which means that it’s way faster to compute.
它做了充分地简化 类似从远处观察一个毛发模型 或者
This simplification is sufficient if we look at a model from afar or we look closely at
a hair model that is way thinner than human hair strands.
The near-field model is more faithful to reality, but also more expensive to compute.
最后并且最重要的难题是 如何结合这两者 无论何时我们
And the final, most important puzzle piece is stitching together the two: whenever we
can get away with it, we should use the far-field model, and compute the expensive near-field
model only when it makes a difference visually.
还有一件事 当仓鼠靠近或远离镜头时 我们
And one more thing: as these hamsters get closer or further away from the camera, we
need to make sure that there is no annoying jump when we’re switching models.
如你所见 动画黄油般顺滑 我们观察时能看到漂亮的
And as you can see, the animations are buttery smooth, and when we look at it, we see beautiful
渲染图像 若我们对理论一无所知 我们就不能
rendered images, and if we didn’t know a bit about the theory, we would have no idea about
the multi-scale wizardry under the hood.
论文同样包含了一系列的光路分解 比如 这里
The paper also contains a set of decompositions for different light paths, for instance, here,
you can see a fully rendered image on the left, and different combinations of light
reflection and transmission events.
For instance, R stands for one light reflection, TT for two transmission events, and so on.
The S in the superscript denotes light scattering events.
Adding up all the possible combinations of these Ts and Rs,
we get the photorealistic image on the left.
That’s really cool, loving it!
If you would like to learn more about light simulations, I am holding a full master-level
course on it at the Technical University of Vienna.
And the entirety of this course is available free of charge for everyone.
I got some feedback from you Fellow Scholars that you watched it and enjoyed it quite a bit.
Give it a go!
As always, details are available in the video description.
Thanks for watching and for your generous support, and I’ll see you next time!
亲爱的学者们 这里是Károly Zsolnai-Fehér带来的两分钟论文