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Questions tagged [importance-sampling]

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1answer
49 views

Can't understand the Importance sampling GGX

I've read many articles relating to importance sampling of GGX. However, I still feel confused. The formula of GGX is : And many article says we should use this formula to sample: In the formula, ...
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1answer
138 views

Multiple Importance Sampling in Path tracer produces Dark Images

So I recently implemented Multiple Importance Sampling in my path tracer which was based on next event estimation. The problem is without MIS I get images like, This is obtained by setting ...
3
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1answer
111 views

BSDF sampling versus light sampling

I wish to understand the specific application of Multiple Importance Sampling (MIS) to weighting BSDF sampling and light sampling together. Refer to the following diagram from these Stanford course ...
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1answer
91 views

Path Tracer - sampling dimensions confusion

Suppose my path tracer is shooting 64 rays per pixel (in an 8x8 grid). The confusion is, when accounting for Global illumination, should I shoot additional X number ...
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0answers
95 views

Handling shadow acne for dynamic surfaces

My path-tracer is generally fine and gives good output for regular test scenes, but I've noticed dense fireflies and dark speckles over fractal surfaces. The noise disappears if I render without light ...
2
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1answer
105 views

Importance Sampling in Unreal Engine Formula Derivation (Irradiance term)

I am currently trying to understand IBL in Unreal Engine, and there are so much things that I don't understand about the formula. Unreal approximate the specular term of shading equation by doing ...
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0answers
42 views

Reverse PDF updates for s-2 or t-2 vertices in MIS for BDPT

MIS weights for BDPT are calculated with ratios of PDFs for each vertex under different types of light transport (radiance vs. importance). These probabilities are regenerated for frontier vertices ...
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0answers
209 views

Wrong output while implementing GGX importance sampling

I'm receiving a non-energy conserving output while trying to importance sample the GGX Distributionof the Microfacet model, which is generally 3-4 times bigger than the resulting PDF I'm following ...
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1answer
143 views

Direct illumination, specular surfaces, and MIS

Multiple Importance Sampling (MIS) is a technique used by Veach's VCM technique to balance responses of different surfaces to different types of importance sampling for direct illumination. My ...
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0answers
51 views

How to make Convolved Diffuse and Specular image in C#

I am trying to take either a HDR panoramic or HDR cubeMap and from that create a Lambert Irradiance environment map and a Cook-Torrence Specular environment map. I am stuck at the proper ...
2
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1answer
231 views

Power heuristic in multiple importance sampling

Both Mitsuba and Tungsten use the power heuristic to do multiple importance sampling (MIS). Mitsuba: ...
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0answers
87 views

An example of Combining Stratified Sampling and Importance Sampling in AGI

Being confused about the example of Combining Stratified Sampling and Importance Sampling in Advanced Global Illumination (P72,P73). I know how to do importance sampling and stratified sampling. But ...
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2answers
4k views

What is Importance Sampling?

What is importance sampling? Every article I read about it mentions 'PDF' what is that as well? From what I gather, importance sampling is a technique to only sample areas on a hemisphere that matter ...
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1answer
424 views

Efficiently sampling specific surfaces using MIS in path tracing

Apologies for posting two questions in one post, but as they are relevant I kept them in one. Question 1 In the definition of multi sample estimator that Veach has defined, the integrand is the same ...
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2answers
530 views

Generation of stratified cosine weighted samples on hemisphere

I have had luck with cosine weighted hemisphere samples, and I know how to generate stratified uniform samples, but I wanted to experiment with combining the two. However, how do I correctly stratify ...
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1answer
2k views

Does cosine weighted hemisphere sampling still require NdotL when calculating contribution for indirect light?

When converting from uniform hemisphere sampling to cosine weighted hemisphere sampling I am confused by a statement in an article. My current indirect contribution is calculated as: ...
7
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1answer
1k views

Path weight for direct light sampling

I originally wrote a pathtracer that just bounces by the BRDF and each sample is added to a buffer that divides by the current number of frames. Now I'd like to do next event estimation at each ...
3
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0answers
446 views

How to properly implement Phong material and importance sample it in a path tracer?

I'm recently implementing Phong materials in my path tracer. My implementation of a randomly sampled Phong material works and looks fine. But it doesn't work well if the shininess(aka power) is too ...
12
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3answers
1k views

Importance Sampling of Environment Maps

What is the best currently known and ideally also production-verified approach for sampling environment maps (EM) in a MIS-based uni-directional path tracer and similar types of renderers? I would ...
7
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1answer
88 views

using importance sampling to reduce the error of outscattered radiance

http://renderman.pixar.com/view/implementing-a-skin-bssrdf In this paper on subsurface scattering, I'm trying to understand how importance sampling is used to compute single scattering. It says that ...
11
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1answer
750 views

What is the difference between importance sampling and mutiple importance sampling?

I can't understand math equations. I'm a graphic designer. What is "importance sampling"? What is "multiple importance sampling"? Could you explain easily, using illustrations and no math equations? ...
4
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1answer
557 views

Multiple Importance Sampling with more than one light

(Note: This has been cross posted from my ompf2 post.) Recently I've implemented Multiple Importance Sampling for the sampling of surfaces in my ray tracer. I do this by, on each intersection, ...