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### #ActualL. Spiro

Posted 10 February 2013 - 07:35 AM

As an employee of tri-Ace I can confirm that we use the Fresnel approximation.  In the world of graphics, “approximation” always means “less accurate, but faster.”

But to use the Fresnel term to modify the diffuse is not always correct.
Imagine if the specular color is [0, 0, 0].  It is the same as there being no specular term.  Which means if you try to balance the energy between the specular and diffuse by just using the Fresnel term, and if the Fresnel term is close to 1, you would have multiplied the diffuse by almost 0 and yet added almost nothing from the specular term.  Since energy conservation depends on how much gets reflected directly as the specular term vs. how much gets reflected as the diffuse term, the balance depends on the specular term itself as well as other factors (such as microfacets).

But I am not the originator of those papers, my boss is.  And I am still learning from him the wonderful world of physically based rendering.
I don’t know yet myself how to balance the terms for every rendering equation, but I am learning, and I know enough to at least say that the Fresnel term alone is not enough.
To be quite frank, I would love it if anyone could post how to go about balancing these terms for any rendering equation.  Not to be spoon-fed the way for just one equation, but to be taught the method I could use to determine a solution for any equation.

L. Spiro

### #2L. Spiro

Posted 03 February 2013 - 06:00 AM

As an employee of tri-Ace I can confirm that we use the Fresnel approximation.  In the world of graphics, “approximation” always means “less accurate, but faster.”

But to use the Fresnel term to modify the diffuse is not always correct.

Imagine if the specular color is [0, 0, 0].  It is the same as there being no specular term.  Which means if you try to balance the energy between the specular and diffuse by just using the Fresnel term, and if the Fresnel term is close to 1, you would have multiplied the diffuse by almost 0 and yet not added almost nothing from the specular term.  Since energy conservation depends on how much gets reflected directly as the specular term vs. how much gets reflected as the diffuse term, the balance depends on the specular term itself as well as other factors (such as microfacets).

But I am not the originator of those papers, my boss is.  And I am still learning from him the wonderful world of physically based rendering.

I don’t know yet myself how to balance the terms for every rendering equation, but I am learning, and I know enough to at least say that the Fresnel term alone is not enough.

To be quite frank, I would love it if anyone could post how to go about balancing these terms for any rendering equation.  Not to be spoon-fed the way for just one equation, but to be taught the method I could use to determine a solution for any equation.

L. Spiro

### #1L. Spiro

Posted 03 February 2013 - 06:00 AM

As an employee of tri-Ace I can confirm that we use the Fresnel approximation.  In the world of graphics, “approximation” always means “less accurate, but faster.”

But to use the Fresnel term to modify the diffuse is not always correct.

Imagine if the specular color is [0, 0, 0].  It is the same as there being no specular term.  Which means if you try to balance the energy between the specular and diffuse by just using the Fresnel term, and if the Fresnel term is close to 1, you would have multiplied the diffuse by almost 0 and yet not added almost anything from the specular term.  Since energy conservation depends on how much gets reflected directly as the specular term vs. how much gets reflected as the diffuse term, the balance depends on the specular term itself as well as other factors (such as microfacets).

But I am not the originator of those papers, my boss is.  And I am still learning from him the wonderful world of physically based rendering.

I don’t know yet myself how to balance the terms for every rendering equation, but I am learning, and I know enough to at least say that the Fresnel term alone is not enough.

To be quite frank, I would love it if anyone could post how to go about balancing these terms for any rendering equation.  Not to be spoon-fed the way for just one equation, but to be taught the method I could use to determine a solution for any equation.

L. Spiro

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