<p>PBRT3 is a really good resource and has a lot of brdfs in it. The book and source code are available for free online.</p>
<p>Regarding oren-nayar, from what I can gather they are just using cosine weighted hemisphere sampling.</p>
<p><a href="https://pbr-book.org/3ed-2018/Light_Transport_I_Surface_Reflection/Sampling_Reflection_Functions" rel="nofollow noreferrer">https://pbr-book.org/3ed-2018/Light_Transport_I_Surface_Reflection/Sampling_Reflection_Functions</a></p>

CC BY-SA 4.0
2021-06-03T18:13:15.853Z
2021-06-03T18:13:15.853Z
Peter
<p>I am currently working on BRDF and their associated probability density functions (PDF) in order to importance-sample them. It is really hard for me to find the correct way to compute the PDF of a BRDF. I know some characteristics that the PDF should verify (the integral must be equal to 1...) but I have really no idea about how to do it.</p>
<p>I am now working on the Oren-Nayar BRDF.</p>
<p>If someone knows a generic way to do it or has any good resources to propose, I will be happy to read that!</p>
<p>Thank you very much by advance,</p>

CC BY-SA 4.0
2021-06-01T18:09:57.120Z
What do you mean by the PDF associated to a BRDF? Do you mean the distribution of normals (NDF), or something else?
Nathan Reed
CC BY-SA 4.0
2021-06-02T06:55:14.400Z
@NathanReed - I think he is talking about the PDF used to sample rays from when trying to sample w.r.t brdfs
gallickgunner
CC BY-SA 4.0
2021-06-02T07:34:34.947Z
@NathanReed you are right, thanks. This is the PDF I am talking about. I will update my post.
Balfar
<brdf><pdf>
How to find the importance sampling function for a specified BRDF?
Balfar
# How to find the importance sampling function for a specified BRDF?

(Asked by: username_0 on 2021-06-01)

I am currently working on BRDF and their associated probability density functions (PDF) in order to importance-sample them. It is really hard for me to find the correct way to compute the PDF of a BRDF. I know some characteristics that the PDF should verify (the integral must be equal to 1...) but I have really no idea about how to do it.

I am now working on the Oren-Nayar BRDF.

If someone knows a generic way to do it or has any good resources to propose, I will be happy to read that!

Thank you very much by advance,

**Tags:** brdf, pdf

> **Comments:**
> **username_1**: What do you mean by the PDF associated to a BRDF? Do you mean the distribution of normals (NDF), or something else?  
> **username_2**: @username_1 - I think he is talking about the PDF used to sample rays from when trying to sample w.r.t brdfs  
> **username_0**: @username_1 you are right, thanks. This is the PDF I am talking about. I will update my post.  

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## 1 answers

### Answer by username_3 on 2021-06-03. Score: 1

PBRT3 is a really good resource and has a lot of brdfs in it. The book and source code are available for free online.

Regarding oren-nayar, from what I can gather they are just using cosine weighted hemisphere sampling.

<https://pbr-book.org/3ed-2018/Light_Transport_I_Surface_Reflection/Sampling_Reflection_Functions>


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