Strictly speaking, dielectrics are not necessarily insulators. For example, salt water is a reasonable conductor but also a dielectric. The term "dielectric" tends to show up in discussion of the Fresnel effect—how reflectance and transmittance vary with angle. Dielectric materials (i.e. nonmetals) are contrasted with metallic materials as they have ...


Unfortunately, the iridescence model is not made to be applied to a diffuse term. Pascal and I made it for microfacet models only (that is the specular term). One way to understand how to include it to a game engine might be to look at Unity's HDRP implementation. In the Lit.hlsl to see how to incorporate the iridescence Fresnel into a specular + diffuse ...


It is not especially related to graphics but physics, and especially, interaction between electromagnetic waves (like light) and matter, i.e. microphysics of optics. Metals have free electrons, and thus it's quite a sea of almost free moving charges that are interacting with the EM field. Ideally, it would be totally reflected. In dielectrics the electrons ...


It turns out that the ring was happening from a negative divided by a negative, so adding nom = max(nom, 0.0); fixed the problem. The new highlight, amplified:


We have $t_{12} = t_{21}$, by the law of reciprocity. Also, $$r_{12} + t_{12} = 1\\r_{21} + t_{21} = 1$$ It follows that $r_{12} = r_{21}$ as well.

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