<p>BRDFs are not accurate for any dielectric surface, as all of them have some degree of subsurface scattering. A BSSRDF is also just an approximation based on the assumption of a semi-infinite slab. Ideally, you'd run a volumetric path trace for all surfaces, which would be much more accurate than BRDFs or BSSRDFs, but significantly more expensive. Although, Disney has already used brute force path tracing over BSSRDFs in production, see <a href="http://blog.selfshadow.com/publications/s2015-shading-course/burley/s2015_pbs_disney_bsdf_notes.pdf" rel="noreferrer">the SIGGRAPH 2015 course notes, section 2.5</a>.</p>

CC BY-SA 3.0
2017-01-09T19:51:20.567Z
2017-01-09T19:51:20.567Z
Stefan Werner
<p>I  am looking for theoretical and implemented models to represent surface materials in software that strives for physical accuracy.</p>

<p>Is BRDF really the best model? What alternatives are better? Why? What drawbacks beside performance do these models have?</p>

CC BY-SA 3.0
2016-12-04T02:47:51.550Z
There's bsdf which is the full sphere instead of just the positive hemisphere that you get with brdf.  That makes it include refraction instead of just reflection.  That doesn't handle subsurface scattering though.  There's also "participating media" to think about which is stuff like fog in the air.  Also, you may have different reflection/refraction properties for different wavelengths of light.  How much of this stuff do you care about? (:
Alan Wolfe
CC BY-SA 3.0
2016-12-04T03:15:46.920Z
Im just curious:)
Mr. Developerdude
CC BY-SA 3.0
2016-12-04T21:31:22.893Z
A BSDF (a complete scattering function, including BRDF (reflection part), BTDF (transmission part), and BSSRDF (subsurface part)) as part of the rendering equation, should be "the best" model, just with a couple of caveats. First, there is not one BSDF model but many, each with different tradeoffs. So it really comes down to which BSDF/BRDF you use. Second, they often assume "particle optics" and skip the wave properties of light. That's a drawback that means that you can't model some phenomena. (Polarization, and "CD diffraction", e.g.)
Supernormal
<physically-based><brdf><material>
What is the most physically accurate model of surface materials possible in computer graphics?
Mr. Developerdude
# What is the most physically accurate model of surface materials possible in computer graphics?

(Asked by: username_0 on 2016-12-04)

I am looking for theoretical and implemented models to represent surface materials in software that strives for physical accuracy.

Is BRDF really the best model? What alternatives are better? Why? What drawbacks beside performance do these models have?

**Tags:** physically-based, brdf, material

> **Comments:**
> **username_1**: There's bsdf which is the full sphere instead of just the positive hemisphere that you get with brdf.  That makes it include refraction instead of just reflection.  That doesn't handle subsurface scattering though.  There's also "participating media" to think about which is stuff like fog in the air.  Also, you may have different reflection/refraction properties for different wavelengths of light.  How much of this stuff do you care about? (:  
> **username_0**: Im just curious:)  
> **username_2**: A BSDF (a complete scattering function, including BRDF (reflection part), BTDF (transmission part), and BSSRDF (subsurface part)) as part of the rendering equation, should be "the best" model, just with a couple of caveats. First, there is not one BSDF model but many, each with different tradeoffs. So it really comes down to which BSDF/BRDF you use. Second, they often assume "particle optics" and skip the wave properties of light. That's a drawback that means that you can't model some phenomena. (Polarization, and "CD diffraction", e.g.)  

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## 1 answers

### Answer by username_3 on 2017-01-09. Score: 4

BRDFs are not accurate for any dielectric surface, as all of them have some degree of subsurface scattering. A BSSRDF is also just an approximation based on the assumption of a semi-infinite slab. Ideally, you'd run a volumetric path trace for all surfaces, which would be much more accurate than BRDFs or BSSRDFs, but significantly more expensive. Although, Disney has already used brute force path tracing over BSSRDFs in production, see [the SIGGRAPH 2015 course notes, section 2.5](http://blog.selfshadow.com/publications/s2015-shading-course/burley/s2015_pbs_disney_bsdf_notes.pdf).


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