bidirectional path tracing
bidirectional path tracing
i was wondering if anybody could please tell me what bidirectional path tracing actualy does and what its advantages are. i have looked everywhere and the most i could find was that little snipit in the blender exporter manual about it not working too well and something about it having superpaths which just confused me further.
Hmm, is there a pdf about the other method? Is this Monte Carlo btw.?Zom-B wrote:Googel is your Friend Dude>>PDF link<<
"Googel is you friend" means translated: try a Googel SearchHmm, is there a pdf about the other method? Is this Monte Carlo btw.?
The algorithms like Monte Carlo & BiDir aren't inventions by Nick,
but by some other guys, so if you are looking for detailed Infos,
the world wide web is the source...
so >>here<< a paper for Monte Carlo Path tracing...
polygonmanufaktur.de
I have a spare 10 minutes so here goes...
Monte Carlo Sampling
One of the big problems in any global illumination renderer is deciding how much light is incident on a particular surface.
A diffuse surface, for example, receives light from all directions and reflects it back equally in all directions. Determining how much light is reflected from a diffuse surface requires calculating all the incident light, which depends on light from direct lightsources and the light reflected by all other surfaces in the scene.
Obviously, it's impossible to calculate every single lighting contribution from all of the infinite number of points in the whole scene, this would take forever.
Monte-carlo sampling is simple a way of estimating this incident light by taking a finite number of samples from all the possible directions of incoming light. A simple way of monte-carlo sampling a diffuse surface would be to shoot 50 rays in random directions from the surface point and then seeing how much light is emitted/reflected from the surfaces that the rays finally intersect. There are a number of different ways of choosing exactly how many rays, and their directions, which all lead to better estimates (e.g. stratified sampling, QMC sampling, importance sampling etc.) but the basic method remains the same.
The name "monte-carlo" comes from the concept of randomness, embodied by the roulette wheel so popular in Monaco
Path-tracing
A technique to reverse trace a ray of light, and its subsequent bounces around the scene, to estimate the amount of light (i.e. radiance) contributed by that path. The term "path-tracing" usually refers only to paths traced from an observer towards the light sources.
A path is often referred to as "implicit" (i.e. it migrates randomly around the scene and is lucky enough to hit a light-source) or "explicit" (after a few bounces, it's not managed to find a light-source, so the end of the path is explicitly connected to a random light-source).
Bi-directional Path-tracing
One path is sent out from the eye/camera and another is generated starting at a light-source. The end-points of both paths are connected together in order to generate a complete path from eye to light.
That's it in a nutshell. As already pointed out, a Google search will give you a lot more information, but any PDF you might find is likely to be awash with PhD-level maths
Path-tracing is great for estimating direct light. Bi-directional path tracing is better for tricky indirect lighting situations and caustics. MLT can be applied to either to improve the accuracy of the estimate.
All of the above is a very simplistic description but hopefully answers your question...
Ian.
Monte Carlo Sampling
One of the big problems in any global illumination renderer is deciding how much light is incident on a particular surface.
A diffuse surface, for example, receives light from all directions and reflects it back equally in all directions. Determining how much light is reflected from a diffuse surface requires calculating all the incident light, which depends on light from direct lightsources and the light reflected by all other surfaces in the scene.
Obviously, it's impossible to calculate every single lighting contribution from all of the infinite number of points in the whole scene, this would take forever.
Monte-carlo sampling is simple a way of estimating this incident light by taking a finite number of samples from all the possible directions of incoming light. A simple way of monte-carlo sampling a diffuse surface would be to shoot 50 rays in random directions from the surface point and then seeing how much light is emitted/reflected from the surfaces that the rays finally intersect. There are a number of different ways of choosing exactly how many rays, and their directions, which all lead to better estimates (e.g. stratified sampling, QMC sampling, importance sampling etc.) but the basic method remains the same.
The name "monte-carlo" comes from the concept of randomness, embodied by the roulette wheel so popular in Monaco
Path-tracing
A technique to reverse trace a ray of light, and its subsequent bounces around the scene, to estimate the amount of light (i.e. radiance) contributed by that path. The term "path-tracing" usually refers only to paths traced from an observer towards the light sources.
A path is often referred to as "implicit" (i.e. it migrates randomly around the scene and is lucky enough to hit a light-source) or "explicit" (after a few bounces, it's not managed to find a light-source, so the end of the path is explicitly connected to a random light-source).
Bi-directional Path-tracing
One path is sent out from the eye/camera and another is generated starting at a light-source. The end-points of both paths are connected together in order to generate a complete path from eye to light.
That's it in a nutshell. As already pointed out, a Google search will give you a lot more information, but any PDF you might find is likely to be awash with PhD-level maths
Path-tracing is great for estimating direct light. Bi-directional path tracing is better for tricky indirect lighting situations and caustics. MLT can be applied to either to improve the accuracy of the estimate.
All of the above is a very simplistic description but hopefully answers your question...
Ian.
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