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:
(1): FDH / pi*(N dot V*(N dot L)
(2): FDH / (N dot V)*(N dot L)
(3): FDH / 4*(N dot V)*(N dot L)
Which one is when correct? In PBR: From Theory to Implementation is a conclusive derivation of the first one, but in their original paper Cook and Torrance use the third one without any detailed explanation.
I hope you can help me.
I would also be happy if someone explained to me how to write mathematical formulas in a Stack Overflow post.
