<p>Quite an old post, put based on the comments here and the posted plot,
I fitted a curve leading to the following equation:</p>
<p>smoothness = 0.25 * shininess ^ 0.2</p>

CC BY-SA 4.0
2022-06-01T13:11:59.813Z
2022-06-01T13:11:59.813Z
Mathias Griessen
<p>As you already note, there is no clear cut interpretation/conversion for these values. I think it is even much worse: Depending on your BRDF and internal limitations (like having defined exponents ranging from 2-2048) the interpretation is <em>completely</em> different. Like suggested in the comments, it might be the best to render a series with different values and fit a conversion curve until the value looks intuitive.</p>
<p>A few examples I was able to find some blog posts that mention something about that topic:</p>
<ul>
<li>At Dontnod entertainment they use a &quot;perceptual linear distribution&quot;.
Sébastien Lagarde acknowledges the problem in <a href="https://seblagarde.wordpress.com/2011/08/17/feeding-a-physical-based-lighting-mode/" rel="nofollow noreferrer">this blog post</a> and writes a few notes on that.</li>
<li>Brian Karis uses a squared roughness values in this <a href="http://graphicrants.blogspot.de/2013/08/specular-brdf-reference.html" rel="nofollow noreferrer">Microfacet BRDF overview</a>. This illustrates also nicely how differently  roughness is used in different Normal Distribution Functions. Blinn-Phong power is here defined as <code>2/roughness^4 - 2</code>.</li>
<li>Frostbite uses a squared remapping. ie. Roughness =  (1 − Smoothness)^2
Details about it and their entire material system is explained in section 3.2 of Sebastien Lagarde's <a href="http://www.frostbite.com/wp-content/uploads/2014/11/course_notes_moving_frostbite_to_pbr.pdf" rel="nofollow noreferrer">writeup</a>.</li>
<li><a href="http://simonstechblog.blogspot.de/2011/12/microfacet-brdf.html" rel="nofollow noreferrer">This blog post</a> suggests to define the roughness for a Beckmann distribution from the shininess alpha as:</li>
</ul>
<p><a href="https://i.sstatic.net/1NWdA.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/1NWdA.png" alt="enter image description here" /></a></p>

CC BY-SA 3.0
2015-09-18T17:22:46.927Z
I wonder if it will be helpful to plot the various methods on a single plot. For example - I plotted two of your links here: http://i.imgur.com/YJjIMOQ.png
ap_
CC BY-SA 4.0
2015-09-18T07:30:54.973Z
2022-10-11T16:27:13.907Z
2022-10-11T16:27:13.907Z
Wumpf
<p>Most modern renderers use physically-based materials and their models are often parameterized over roughness. Since this wasn't always the case with renderers, conventional assets often don't have a notion of roughness. Instead, we see "shininess" or "specular power" as a common material parameter.</p>

<p>I understand that there is no exact conversion between the two, but is there a rule-of-thumb / approximate way to get roughness for a material whose specular power or shininess is known?</p>

CC BY-SA 3.0
2015-09-18T06:36:53.597Z
How about rendering a series of comparison swatches and try to fit a conversion curve?
joojaa
<specular><brdf><pbr>
What is the accepted method of converting shininess to roughness, and vice versa?
ap_
# What is the accepted method of converting shininess to roughness, and vice versa?

(Asked by: username_0 on 2015-09-18)

Most modern renderers use physically-based materials and their models are often parameterized over roughness. Since this wasn't always the case with renderers, conventional assets often don't have a notion of roughness. Instead, we see "shininess" or "specular power" as a common material parameter.

I understand that there is no exact conversion between the two, but is there a rule-of-thumb / approximate way to get roughness for a material whose specular power or shininess is known?

**Tags:** specular, brdf, pbr

> **Comments:**
> **username_1**: How about rendering a series of comparison swatches and try to fit a conversion curve?  

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## 2 answers

### Answer by username_3 on 2015-09-18. Score: 14 | Accepted answer

As you already note, there is no clear cut interpretation/conversion for these values. I think it is even much worse: Depending on your BRDF and internal limitations (like having defined exponents ranging from 2-2048) the interpretation is *completely* different. Like suggested in the comments, it might be the best to render a series with different values and fit a conversion curve until the value looks intuitive.

A few examples I was able to find some blog posts that mention something about that topic:

* At Dontnod entertainment they use a "perceptual linear distribution".
  Sébastien Lagarde acknowledges the problem in [this blog post](https://seblagarde.wordpress.com/2011/08/17/feeding-a-physical-based-lighting-mode/) and writes a few notes on that.
* Brian Karis uses a squared roughness values in this [Microfacet BRDF overview](http://graphicrants.blogspot.de/2013/08/specular-brdf-reference.html). This illustrates also nicely how differently roughness is used in different Normal Distribution Functions. Blinn-Phong power is here defined as `2/roughness^4 - 2`.
* Frostbite uses a squared remapping. ie. Roughness = (1 − Smoothness)^2
  Details about it and their entire material system is explained in section 3.2 of Sebastien Lagarde's [writeup](http://www.frostbite.com/wp-content/uploads/2014/11/course_notes_moving_frostbite_to_pbr.pdf).
* [This blog post](http://simonstechblog.blogspot.de/2011/12/microfacet-brdf.html) suggests to define the roughness for a Beckmann distribution from the shininess alpha as:

[![enter image description here](https://i.sstatic.net/1NWdA.png)](https://i.sstatic.net/1NWdA.png)

> **Comments:**
> **username_0**: I wonder if it will be helpful to plot the various methods on a single plot. For example - I plotted two of your links here: http://i.imgur.com/YJjIMOQ.png  

---

### Answer by username_2 on 2022-06-01. Score: 1

Quite an old post, put based on the comments here and the posted plot,
I fitted a curve leading to the following equation:

smoothness = 0.25 \* shininess ^ 0.2


---

