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### #5CryZe

Posted 02 February 2013 - 08:16 PM

Tiago, that's an approximation, even with the real Fresnel equations, but is not really correct.

Fresnel is dependent on the microfacets oriented towards the halfway vector, but diffuse actually is all the light that is not being reflected, not being absorbed and scattered back out, independent of the microfacets oriented towards the halfway vector. So simply the complement of a single fresnel value won't do it. You would need to solve the integral over all the microfacet orientations with a modified microfacet model:

### #4CryZe

Posted 02 February 2013 - 08:16 PM

Tiago, that's an approximation, even with the real Fresnel equations, but is not really correct.

Fresnel is dependent on the microfacets oriented towards the halfway vector, but diffuse actually is all the light that is not being reflected, not being absorbed and scattered back out, independent of the microfacets oriented towards the halfway vector. So simply the complement of a single fresnel value won't do it. You would need to solve the integral over all the microfacet orientations with a modified microfacet model:

http://rogercortesi.com/eqn/tempimagedir/eqn7363.png

### #3CryZe

Posted 02 February 2013 - 08:15 PM

Tiago, that's an approximation, even with the real Fresnel equations, but is not really correct.

Fresnel is dependent on the microfacets oriented towards the halfway vector, but diffuse actually is all the light that is not being reflected, not being absorbed and scattered back out, independent of the microfacets oriented towards the halfway vector. So simply the complement of a single fresnel value won't do it. You would need to solve the integral over all the microfacet orientations with a modified microfacet model:

### #2CryZe

Posted 02 February 2013 - 08:14 PM

Tiago, that's an approximation, even with the real Fresnel equations, but is not really correct.

Fresnel is dependent on the microfacets oriented towards the halfway vector, but diffuse actually is all the light that is not being reflected, not being absorbed and scattered back out, independent of the microfacets oriented towards the halfway vector. So simply the complement of a single fresnel value won't do it. You would need to solve the integral over all the microfacet orientations with a modified microfacet model:

$\int_\Omega \frac {D(n, \omega_m)(1-F(\omega_i, \omega_m))\sqrt{G(n,\omega_i,\omega_i)}} {\pi (n \cdot \omega_i)} \mathrm{d} \omega_m$

### #1CryZe

Posted 02 February 2013 - 08:09 PM

Tiago, that's an approximation, even with the real Fresnel equations, but is not really correct.

Fresnel is dependent on the microfacets oriented towards the halfway vector, but diffuse actually is all the light that is not being reflected, not being absorbed and scattered back out, independent of the microfacets oriented towards the halfway vector. So simply the complement of a single fresnel value won't do it. You would need to solve the integral over all the microfacet orientations with a modified microfacet model (D*(1-F)*sqrt(G)/(pi*N.L)).

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