bssrdf

请问是不是正负两面都加了粒子？
还有你的RESEED是如何处理的？是根据ENRIGHT.2002中的方法做嘛？

效果很不错，楼主厉害。我最近也在实现这个东西，请问具体是怎么渲染的？能否详细介绍一下。

Could you give the details of your implementation of the bidirectional path tracing algorithm ? I'm trying to implement it in my own raytracer, but it's a nightmare to debug it. I think that i've misunderstood a part of the theory, so if you could help me, I would greatly appreciate it! Thanks

@LoveGraphics
我直接ray trace的level set, 所以这一步就省略了。

http://dalab.se.sjtu.edu.cn/~jietan
这里有我同学做的，希望大家多交流交流

使用PLS重构曲面的时间效率大约是多少？

哈哈，我前一阵子也在弄这个，也用了PLS，但是感觉水还是损耗的很快，不知道你是怎么解决的呢？

@BSSRDF
恐怕批处理不是商业渲染的解决方案吧

@yuanhong
pbrt可以渲染动画的，批处理就是了。

效果很酷！pbrt的话，怎么达到动态渲染效果呢？

对了， 你是用什么方法把它做成影片的

lz是不是只用google talk呢？没用过啊，呵呵。

Can't believe someone in China could get access to such a fantastic book. How did you get it?

I've briefly looked through PBRT source code, not as well written and organized as I expected. And as an effort to lay a good foundation in rendering, I am building my distributed ray-tracer from scratch.

Hope to get in touch with you in the future.

Hi, 请问你是从哪里买到PBRT的呢？我对这本书很有兴趣。

@yuanhong
point repulsion是Greg Turk在他的博士论文"Texturing Surfaces Using Reaction-Diffusion"里提出的方法。 这种方法可以在一个多边形模型上均匀取点。这样取的点就可以满足Jensen方法的要求。可惜我的point repulsion实现还是有些问题。现在我必须取比[A/(pi*lu*lu)]更多的点。
至于计算irradiance， 我PHOTONMAP和DIRECTLIGHTING都用了。效果差不多。而PHOTONMAP我只用了DIRECT MAP。我想interreflection部分并不重要。

你可以在google talk找到我：bssrdf@gmail.com

@yuanhong
noise应该是采样产生的。
好办法应该是对每像素多射入光线，当然这样会影响速度。
还有个方法是对更好的概率密度进行采样，这个比较复杂。

通过对比可以看到你的方法要好很多啊！
我想问问关于图中噪声(不知恰不恰当)是如何引起的呢？有没有什么好的办法解决呢？

我也是预处理花了很多时间，我跑dragon时，大概用了40多分钟。
我的采样是用别人的一个方法，在三角形内均匀取点，使他们之间的距离大概是lu。
point repulsion是什么？能给我解释下么？
在计算irradiance时，我用的是最简单的direct lighting,而且我把interreflection 那部分也省去了，所以我的实现并不好。
能和你进一步交流么？
我qq:330814441 MSN:timothy_yuanhong@hotmail.com

@yuanhong
你实现的效果也很好呀！
我用的就是Jensen and Buhler（2002）那篇文章。很多人的实现都是基于这片文章，可能是因为比较容易变成代码吧。buddha scene在我的机器上跑的时间不长，具体的时间不记得了。最费时间的是预处理。
一个问题，你在你的实现里是怎么取的sample point？你用了point repulsion了吗？还有，你计算irradiance的时候，用的是photon map还是别的方法？
很高兴和你交流一些心得体会。

楼主你的实现效果很不错啊！
你用的是Jensen 2002 3s paper上的算法么？不知在你机器上跑budaha的时间长不长？
很愿意和你就3s和图形学方面的问题进行交流！

@mz
I am doing it out of interest and yes, I read a lot of papers.
PBRT book is worthwhile to get. Without it, it's going to be a nightmare to implement these more advanced algorithms. Of course you can use many open source ray tracers, but none of them has a detailed explanation as in PBRT.

@MLJack
The glass is just the combination of specular reflection and transmission as defined in PBRT.
As Veach's thesis shows, the weight of the path when there are specular vertices is easy to calculate by setting corresponding PDFs to zero. However, the problem with these specular vertices is that no connection made to them such that some effects associated with them can only be obtained by standard path tracing. For those parts of the image, BPT is as noisy as PT, e.g., the glass sphere.

Haven't tried glossy BTDF yet. Interesting to see though.

cong!

i also migrate this algorithm from RenderPark. :)

"Testing Monte-Carlo Global Illumination Methods with Analytically Computable Scenes"

The diffuse ball described this paper is highly valuable in debuging process. All pdfs for surface area are constant. It provide hints for unbiased estimation and bug finding.

btw, which material you used to show the refraction caustic?
Is it the refraction specular BTDF in glass?
It needs a special tag in the weight computing as it's a deta function.
Have you try any glossy BTDF?

很羡慕你，有PBRT看，可以省下不少时间。
基于物理的渲染很费时间，国内公司很少有做这个的，
我对这个很感兴趣，深入研究这个要读很多论文。
问题就是学了不一定能找到这样的公司，麻烦。
想问一下BSSRDF,你把这个是作为兴趣，还是工作就是做这个的？

楼主，我也是做渲染器的，我也在研究pbrt,能交流一下吗》
我的msn:cloudseawang@hotmail.com
gmail:cloduseawang@gmail.com
QQ 37771270

@AdamGamer
No way for this kind of images to be rendered in real time, at least not in the near future.

Well, the most useful reference I found is Jensen's book "Realistic image synthesis using photon mapping". Jensen and Christensen's 1998 paper is also helpful. Another worthwhile book is "Advanced global illumination".

Good work.
Is the image yor posted rendered in real time?

amazing!
can you suggest some papers on this area?Thanks

@billconan
Maxwell is a Monte Carlo ray tracer using MLT algorithm. Pbrt is also a MC ray tracer, only that it uses other global illumination algorithms, e.g., Path Tracing, Irradiance Caching, Photon Mapping. You can make Pbrt implementing MLT, but a lot of work has to be done.

可是我觉得pbrt.org那个配套书上讲的好象是光线追踪渲染器啊，mlt不是那种像maxwell似的渲染器么？

不好意思，还有个问题。
就是物体本身的颜色怎样计算，在室外的物体把太阳当做光源，用render equation计算？还是有别的方法计算？

由光谱值向CIE X，Y，Z转化是应用光谱采样，用离散的公式计算出来的。
但是怎样求根据CIE X，Y，Z所对应波长的光谱值呢？

@li kong
I wrote a function which transforms SPD (spectrum data) to RGB through XYZ.

First you use CIE X,Y,Z data to convert SPD, which is a series of number corresponding to their wavelength, to XYZ. Then XYZ to RGB is straightforward.

你介绍的这些资料我看了，他们使用的是xyY向XYZ转化，然后再转化成
RGB。我用这种方法实现了。
但是论文中skylight 和 sunlight对场景中物体的作用是用光谱计算的，
有个xyY向光谱的转化程序，我没找到具体的转化过程，论文用riS0Spectrum = RiRegularSpectralCurve(S0Amplitudes,300,830,54);
转化，但没有给出初始化的程序。你是怎样实现的？
或许实现Aerial perspective，图象更真实点，建筑上的蓝色太突出了，
使用后应该会削减点。

@li kong
The methods are described in the paper I mentioned above in very much details.

Google that paper's name will give you some additional information, especially a post on gamedev.net.

将光谱转化成RGB的方法是怎样实现的？
有什么好的参考资料？

it need be reforged.

The paper is "A Practical Analytic Model for Daylight" by A. J. Preetham et al. (1999). The method from this paper has been used in Nextlimit Maxwell, the most advanced ray tracer today.

All the equations are listed in the paper, along with the c++ source code on their website (http://www.cs.utah.edu/vissim/papers/sunsky/).

呵呵，效果不错。
用的哪篇论文的算法？计算太阳的Intensity和位置用的哪个公式？
谢谢。
我最近也在做这方面的工作，我msn:chena224503@hotmail.com，有空聊聊啊。

@mljack_
I am using PBRT (www.pbrt.org) code to implement the MLT algorithm. There is still much work to be done.

Good work!!!
Btw, which renderer you use? self-made or some open-source renderer?

hi ！ 我也是写渲染器的，能和你交流一下吗？
我的
QQ: 25768200
MSN: mayaxprman@hotmail.com
email: chaos.chiao@gmail.com