• ## PathTracing

千次阅读 2019-01-18 10:33:10
Path Tracing 懒得翻译了，相信搞图形学的人都能看得懂，2333 Path Tracing is a rendering algorithm similar to ray tracing in which rays are cast from a virtual camera and traced through a simulated ...
Path Tracing
懒得翻译了，相信搞图形学的人都能看得懂，2333
Path Tracing is a rendering algorithm similar to ray tracing in which rays are cast from a virtual camera and traced through a simulated scene. Path tracing uses random sampling to incrementally compute a final image. The random sampling process makes it possible to render some complex phenomena which are not handled in regular ray tracing, but it generally takes longer time to produce a high quality path traced image.
The random sampling in path tracing causes noise to appear in the rendered image. The noise is removed by letting the algorithm generate more samples, i.e. color values resulting from a single ray. A more in-depth explanation of the path tracing algorithm is given below.
Random Sampling
In path tracing rays are distributed randomly within each pixel in camera space and at each intersection with an object in the scene a new reflection ray, pointing in a random direction, is generated. After some number of bounces each ray eventually exits the scene or is absorbed. When a ray has finished boucing about in the scene a sample value is calculated based on the objects the ray bounced against. The sample value is added to the average for the source pixel.
The samples in a path-traced image are distributed evenly over all pixels. The color of each pixel is the average of all the sample values computed for that pixel.
The random components in path tracing cause the rendered image to appear noisy. The noise decreases over time as more and more samples are calculated.
Samples Per Pixel (SPP)
The defining factor for render quality is the number of samples per pixel (SPP).

The higher SPP you have in a rendered image the less noise will be noticeable. However the added quality per sample decreases the more samples you have already (since each sample is just contributing to an average over all samples). The difference in image quality between, for example, 20,000 SSP and 21,000 SSP will not be as noticeable as between 1,000 SSP and 2,000 SSP.
Sunlight does not require high SSP to give a nice image. Outdoor scenes can be rendered with relatively low SPP if sunlight is enabled. Emitters (torches, lava, glowstone, pumpkins, etc.) require a lot of SSP to reduce the noise, so indoor scenes and similar scenes in low-light environments take a much higher SPP number to look good.
Render Time
There is no definite answer to how long it will take to render a scene. The general guideline is that the longer you render an image, the better it will become. Take into account the diminishing returns explained above.
The time required to render a nice looking image depends on how well-lit the scene is, how many samples per second the renderer can produce (depending on how fast your CPU is), and how many pixels the canvas has.
Scaling the canvas has an effect on render time proportional to the pixel area of the canvas. An image of 800 by 800 pixels will take four times as long time to achieve the same quality as an image of 400 by 400 pixels since the total number of pixels has quadrupled. If your renders are taking too long, you can reduce the canvas size for quicker results.
Small but bright light sources, such as torches, add a lot of noise to a scene. It takes especially long time to render a scene lit mostly by a few torches. This is an unfortunate and unavoidable disadvantage of the Path Tracing rendering method.
The reason for this effect is based on the low probability for each sampled light path to include the torches, versus the high luminance of the object. The final render takes the average of all sampled values, but the average can be "too high" for a long time because of the high luminance. The average will decrease over time, but for a while there may be one pixel that has been lit by a particular light source in a neighborhood of several pixels that will stand out sharply against the others that have not yet been lit by the same source, hence the bright dots seen above at low sample counts.
SPP Comparisons
An indoor scene rendered with increasing SPP. The white numbers show SPP:

https://chunky.llbit.se/path_tracing.html
展开全文
• THREE.js-PathTracing-Renderer 在Three.js WebGL框架之上，具有全局照明和渐进式渲染的实时PathTracing。 现场演示 演示了一些用于射线追踪的原始形状。 将射线追踪与射线行进相结合，并在真实的物理天空下模拟了...
• Path Tracing PT主要是为了解决RT中无法处理漫反射的问题。 下图分别为直接光照（无漫反射）和全局光照的结果区别。(color bleeding) solution 1 simple Monte Carlo 使用Monte Carlo公式求解渲染方程，得到以下...
Path Tracing
PT主要是为了解决RT中无法处理漫反射的问题。
下图分别为直接光照（无漫反射）和全局光照的结果区别。(color bleeding)

solution 1 simple Monte Carlo
使用Monte Carlo公式求解渲染方程，得到以下解决方案：

随机地选择N条光线，向外射出，查看其是否可以打到光源上。
solution 2 Global Illumination
上述表达式有一个问题，当射出的光线没有打到光源，而是打到了另一个物体上时，应该怎么做？

solution 3 Path Tracing

solution 4 Russian Roulette(RR)
上述方案依旧有问题——对于递归而言，何时才是递归的终止条件？
由简单的概率论知识我们就可以得到：E = p*(Lo/p)+(1-p)*0 = Lo
所以可以由此得到以下伪代码：

solution 5 sampling the light
由以上四个方案组成了一个正确的PT的解决方案。
但是PT还有一些问题，比如在low spp的情况下，噪声非常大。

注：spp（sample per pixel）指的是一个像素内打出的光线数。

如下图，绿色像素的spp为3。

light source（直接从光源采样，不需要RR）  other reflectors（间接的，需要RR）
最后得到伪代码：
展开全文
• ## Pathtracing 实现

千次阅读 2011-09-02 17:49:27
渲染器已经断断续续做了三个月的时间了，加...这周加入了path tracing算法和OpenMP多线程支持。 贴几张图 Path tracing收敛速度实在是慢啊.... 还好OpenMP用起来比较简单，几行代码就可以把程序并行了。
 渲染器已经断断续续做了三个月的时间了，加了一些基本的功能。 这周加入了path tracing算法和OpenMP多线程支持。 贴几张图

Path tracing收敛速度实在是慢啊.... 还好OpenMP用起来比较简单，几行代码就可以把程序并行了。这个并行过程比CUDA方便多了，虽然没有CUDA并行粒度高，不过也算是利用多核计算了。 源代码：http://sourceforge.net/projects/soraytrace/
展开全文
• THREE.js-PathTracing-Renderer 在Three.js WebGL框架之上，具有全局照明和渐进式渲染的实时PathTracing。 现场演示 演示了一些用于射线追踪的原始形状。 将射线追踪与射线行进相结合，并在真实的物理天空下模拟了...
• A simple path tracing renderer. Here are some results. I made the scene using 3ds max. It is my dormitory in South China University of Technology. Here is my seat. null ...

A simple path tracing renderer.
Here are some results.

I made the scene using 3ds max.
It is my dormitory in South China University of Technology.

Here is my seat.

null

转载于:https://www.cnblogs.com/dydx/p/6329732.html
展开全文
• bidirectional pathtracing算法是继pathtracing算法以来的又一个突破。因为经典pathtracing算法有一个很大的问题就是效率极低，每个像素点发出的每个path必须击中光源才会对该像素点的颜色值有所贡献，否则这整条...
• 上面说到pathtracing（pt）的一些优点和缺点，优点即其实现很简单，这就是大概为什么当今市面上流行的很多渲染器如今都相继采用pathtracing算法为核心进行实现，但是pathtracing的最大缺点就是收敛速度很慢，其原因...
• 一.目的 1.想知道：如何使用:...【虚幻4】_UE4十分钟学会超高质量影视图像渲染PathTracing，媲美VRay和Arnold_哔哩哔哩_bilibili【虚幻4】_UE4十分钟学会超高质量影视图像渲染PathTracing，媲美VRay和Arnoldhttps://...
• 路径追踪画布 为了学习，我在观看使用 javascript 实现了跟踪。... pathtracing-canvas 根据知识共享署名-相同方式共享 3.0 未移植许可证获得许可。 你应该已经收到了这份工作的许可证副本。如果没有，请参阅 。
• 之前了解了路径追踪，参考如下： Q124：PBRT-V3，“路径追踪”积分器（14.5章节）接下来，先回忆一下Path Tracing，然后具体了解Bidirectional Path Tracing
• 一.Monte Carlo Integration 作用:给定一个函数,计算其定积分 在b-a区间内均匀采样xi...二.path tracing (注意区别Ray tracing) whitted-style ray tracing 认为物体表面反射沿镜面反射方向,若对于粗糙物体,则...
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• 本节实现了一个最简单的基于pathtracing的光线跟踪方法，使用了基于随机微平面的理论，我们认为光线击到任何一处，它的反射方向是随机的，因为这一处可以划分为无穷小，现实世界的某一点也是吸收了几乎可以认为是...
• 89.1 Path Tracing只用于间接光照   根据Path Trace的算法，只有当最终的反射光线撞击到发光材质物体时，才会对最初的撞击点进行“有效”着色，否则着色为“黑色”。这就给图形带来大量的噪声。所以，接下来，...
• https://jacco.ompf2.com/2019/07/18/wavefront-path-tracing/
• Spent some time on bidirectional path tracing(BPT) in PBRT. At many parts of the code, I had to do it by try and error. Debugging is a pain. The implementation may still be wrong in some details, but ...
• 辐射度量学
• 一、先上图： 左边整个渲染过程耗时：1小时 右边整个渲染过程耗时：35小时（未用多线程） 还是右边好看点（tmd当然了） 二：代码 Vector3f Scene::castRay(const Ray &ray, int depth) const ...
• 前文提及了光线追踪的一些常用手法，但是其中path tracing的实现最为简单，但是其最致命的一个缺点就是图像收敛速度很慢。。原因在于从摄影机发射出的每一条光线若不与场景中的光源相交，则这条光线就是无贡献的，...
• https://www.scratchapixel.com/lessons/3d-basic-rendering/global-illumination-path-tracing/introduction-global-illumination-path-tracing
• 单文件Vulkan路径跟踪 使用Vulkan RayTracing的最小pathtracer 环境 Vulkan SDK 1.2.162.0 支持Vulkan Ray Tracing的GPU /驱动程序 C ++ 17 垃圾焚烧炉 GLM 设置 请参见 参考
• 其核心代码是99行C++代码组成，渲染上述场景是使用unbiased Monte Carlo path tracing (无偏的蒙特卡洛path tracing算法)。 本次博客的目的是介绍smallPT的原理，以及代码对应的意义（主要参考奥克拉荷马州立大学...
• 该文档是利用深度学习将复杂的光线路径追踪技术进行实时化的突破性研究
• 现在理论分析已经足够, 剩下的任务就是求解下面的渲染方程, 接下来即将介绍的路径追踪(Path Tracing)就是一种求解渲染方程的有效手段. 文学式编程 Literate Programming 文式编程是Donald Knuth提出的一种编程范式,...
• http://blog.three-eyed-games.com/2019/03/18/gpu-path-tracing-in-unity-part-3/ “Arithmetic! Algebra! Geometry! Grandiose trinity! Luminous triangle! Whoever has not known you is without sense!” – ...
• Babylon.js-PathTracing-Renderer 具有全局照明和渐进式渲染的实时路径跟踪，所有这些都在 Babylon.js WebGL 框架之上。 点击此处查看现场演示： : 变换二次几何演示： : 注意：根据 Babylon.js 用户的要求，这...

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