<p>In general, artists like working with a linear roughness value between 0 and 1 (similarly for all other material parameters), since this is easier to work with and to understand compared to directly using the parameters of certain BRDF components as presented in the literature. Disney for instance always uses linear material parameters for their Disney BRDF in the range [0,1] from the perspective of the artists (see their <a href="https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf" rel="nofollow noreferrer">course notes</a> on page 18). Working with linear values in the range [0,1] also simplifies storing and loading these values in RGB or sRGB textures.</p>

<p>The actual roughness used in the BRDF equations is non-linear. So one needs to map linear to non-linear roughness in some computationally cheap way that pleases the artists. The most important thing is to be consistent across your renderer and to explicitly specify when a roughness parameter is linear or non-linear.</p>

<p>It is worth reading <a href="https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf" rel="nofollow noreferrer">Moving Frostbite to Physically Based Rendering 3.0</a>. These course notes explicitly use the terminology linear roughness and (non-linear) roughness, both in the text and code samples. Furthermore, it is also worth reading <a href="http://graphicrants.blogspot.be/2013/08/specular-brdf-reference.html" rel="nofollow noreferrer">The Specular BRDF Reference</a> which defines various BRDF components for the Cook-Torrance BRDF using the same non-linear roughness parameter $\alpha$ (defined as the square of the linear roughness $roughness$).</p>

CC BY-SA 3.0
2017-11-18T14:54:55.693Z
Great job at summarizing everything! I'll also make sure to check out the BRDF Reference and test out some of them.
Daniel Kareh
CC BY-SA 3.0
2017-11-18T15:02:09.103Z
@DanielKareh you can also take a look at my [brdf.hlsl](https://github.com/matt77hias/MAGE/blob/master/MAGE/MAGE/shaders/brdf.hlsli) which includes even more BRDF components :)
Matthias
CC BY-SA 3.0
2017-11-22T15:56:24.877Z
Heh, thanks :)The main problem I find is that lots of the lighting models I find on Google or in papers are, I guess, scientific and don't include roughness, so your collection will be pretty useful.
Daniel Kareh
CC BY-SA 3.0
2017-11-14T08:54:25.413Z
2017-11-14T09:00:32.263Z
2017-11-14T09:00:32.263Z
Matthias
<p>I have been recently exploring physically-based rendering (PBR), but there is one part that still confuses me. I don't quite get roughness remapping, as described in the <a href="https://learnopengl.com/#!PBR/Theory/" rel="noreferrer" title="PBR Theory">PBR section</a> on Learn OpenGL. Specifically, scroll down until you find <em>Geometry function</em>. This remapping is described in several other papers / courses as well, such as <a href="https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf/" rel="noreferrer" title="Disney PBR">Disney</a> and <a href="https://cdn2.unrealengine.com/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf/" rel="noreferrer" title="Real Shading in Unreal Engine 4">Epic Game's PBR Course</a>. Is this remapping solely artistic, or is there some physical reasoning in it? A quick answer and explanation would be quite appreciated :)</p>

<p>TL;DR What in the world is roughness remapping for?</p>

CC BY-SA 3.0
2017-11-13T00:12:01.873Z
Ah, that makes sense. So, I'm guessing from your statement, that the remapped roughness is just to make the artists happy, right? It's not required.
Daniel Kareh
CC BY-SA 3.0
2017-11-13T07:18:39.050Z
Yes, it's unnecessary. If you look into Scientific Papers (like the original GGX Paper by Walter et. al), there is no remapping done.

Also from a logical viewpoint, if you use $0.25$ as your roughness or $0.5^2$ as your roughness shouldn't make a difference.
Tare
CC BY-SA 3.0
2017-11-14T00:43:57.673Z
@Matthias: That looks like an interesting read. I'll make sure to read through it, thanks for the link.
Daniel Kareh
CC BY-SA 3.0
2017-11-14T09:01:30.220Z
Edit: I removed my comments to merge them in an answer.
Matthias
<rendering><lighting><brdf><pbr>
Roughness Remapping
Daniel Kareh
# Roughness Remapping

(Asked by: username_0 on 2017-11-12)

I have been recently exploring physically-based rendering (PBR), but there is one part that still confuses me. I don't quite get roughness remapping, as described in the [PBR section](https://learnopengl.com/#!PBR/Theory/ "PBR Theory") on Learn OpenGL. Specifically, scroll down until you find *Geometry function*. This remapping is described in several other papers / courses as well, such as [Disney](https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf/ "Disney PBR") and [Epic Game's PBR Course](https://cdn2.unrealengine.com/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf/ "Real Shading in Unreal Engine 4"). Is this remapping solely artistic, or is there some physical reasoning in it? A quick answer and explanation would be quite appreciated :)

TL;DR What in the world is roughness remapping for?

**Tags:** rendering, lighting, brdf, pbr

> **Comments:**
> **username_0**: Ah, that makes sense. So, I'm guessing from your statement, that the remapped roughness is just to make the artists happy, right? It's not required.  
> **username_1**: Yes, it's unnecessary. If you look into Scientific Papers (like the original GGX Paper by Walter et. al), there is no remapping done.  Also from a logical viewpoint, if you use $0.25$ as your roughness or $0.5^2$ as your roughness shouldn't make a difference.  
> **username_0**: @username_2: That looks like an interesting read. I'll make sure to read through it, thanks for the link.  
> **username_2**: Edit: I removed my comments to merge them in an answer.  

---

## 1 answers

### Answer by username_2 on 2017-11-14. Score: 3 | Accepted answer

In general, artists like working with a linear roughness value between 0 and 1 (similarly for all other material parameters), since this is easier to work with and to understand compared to directly using the parameters of certain BRDF components as presented in the literature. Disney for instance always uses linear material parameters for their Disney BRDF in the range [0,1] from the perspective of the artists (see their [course notes](https://disney-animation.s3.amazonaws.com/library/s2012_pbs_disney_brdf_notes_v2.pdf) on page 18). Working with linear values in the range [0,1] also simplifies storing and loading these values in RGB or sRGB textures.

The actual roughness used in the BRDF equations is non-linear. So one needs to map linear to non-linear roughness in some computationally cheap way that pleases the artists. The most important thing is to be consistent across your renderer and to explicitly specify when a roughness parameter is linear or non-linear.

It is worth reading [Moving Frostbite to Physically Based Rendering 3.0](https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf). These course notes explicitly use the terminology linear roughness and (non-linear) roughness, both in the text and code samples. Furthermore, it is also worth reading [The Specular BRDF Reference](http://graphicrants.blogspot.be/2013/08/specular-brdf-reference.html) which defines various BRDF components for the Cook-Torrance BRDF using the same non-linear roughness parameter $\alpha$ (defined as the square of the linear roughness $roughness$).

> **Comments:**
> **username_0**: Great job at summarizing everything! I'll also make sure to check out the BRDF Reference and test out some of them.  
> **username_2**: @username_0 you can also take a look at my [brdf.hlsl](https://github.com/matt77hias/MAGE/blob/master/MAGE/MAGE/shaders/brdf.hlsli) which includes even more BRDF components :)  
> **username_0**: Heh, thanks :)The main problem I find is that lots of the lighting models I find on Google or in papers are, I guess, scientific and don't include roughness, so your collection will be pretty useful.  

---

