Correct Specular-Term of the Cook-Torrance- Torrance-Sparrow-Model
<p>For a while I have been doing some research on the Topic of PBR and one reflection-models mentioned over and over is the Cook-Torrance-/ Torrance-Sparrow-model and it seems that in any mention or explanation of this model another form of the specular term is used. The versions I have found are:</p>

<p>(1): F<em>D</em>H / pi*(N dot V*(N dot L)</p>

<p>(2): F<em>D</em>H / (N dot V)*(N dot L)</p>

<p>(3): F<em>D</em>H / 4*(N dot V)*(N dot L)</p>

<p>Which one is when correct? In <em>PBR: From Theory to Implementation</em> is a conclusive derivation of the first one, but in their original paper Cook and Torrance use the third one without any detailed explanation.</p>

<p>I hope you can help me.</p>

<p>I would also be happy if someone explained to me how to write mathematical formulas in a Stack Overflow post.</p>