# Tag Info

Accepted

### How to properly combine the diffuse and specular terms?

Using two Fresnel terms is correct in the sense that any given diffuse path will pass through the surface twice. If you're solving diffusion by tracing a path through the medium until it bounces out ...
• 330
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### What is the accepted method of converting shininess to roughness, and vice versa?

As you already note, there is no clear cut interpretation/conversion for these values. I think it is even much worse: Depending on your BRDF and internal limitations (like having defined exponents ...
• 803

### Confused with PBR implementations

DFG pops up in the family of microfacet based BRDFs. It is simply the product of three terms: D : The microfacet distribution. F : The fresnel coefficient. G : The geometric attenuation between ...
• 1,575
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### 16bit half-float linear HDR images as (diffuse/albedo) textures?

In film production, we almost never use 8-bit textures for color/albedo, because of banding, etc. (JPEG is especially problematic since by spec, it's sRGB rather than linear values.) We either use '...
• 206
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### In a physically based BRDF, what vector should be used to compute the Fresnel coefficient?

In Schlick's 1994 paper, "An Inexpensive Model for Physically-Based Rendering", where they derive the approximation, the formula is: F_{\lambda}(u) = f_{\lambda} + (1 - f_{\lambda})(1 - u)^...
• 3,502
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### Rendering in radiometric units or photometric?

It's fine to use photometric units as an overall scale for setting light brightnesses. However, there's a technical subtlety you should be aware of. I'll quote from a blog post I wrote on the subject ...
• 23.7k
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### Why normalise Lambertian BRDF by 1/pi?

I think I got it! Because $cos(\theta)$ integrates to $\pi$ over the hemisphere (and not $2\pi$). And the incoming light is multiplied by $cos(\theta)$ (and the BRDF).
• 460

### In a physically based BRDF, what vector should be used to compute the Fresnel coefficient?

The Fresnel coefficient should be evaluated using $H$, not $N$. You wrote, I have trouble seeing why we can still use that formula in a BRDF, which is supposed to approximate the integral over all ...
• 23.7k

### 16bit half-float linear HDR images as (diffuse/albedo) textures?

Yes, it's possible in some extreme cases for HDR lighting and tonemapping to expose banding issues in color textures. In those cases, having a higher bit depth for the textures could be useful. ...
• 23.7k

### How to properly combine the diffuse and specular terms?

While browsing to properly write my question, I actually found the answer, which happens to be very simple. Another Fresnel term is also going to weight in as the photons make their way out of the ...
• 4,210

### Dealing with blown-out highlights in PBR

Using physically based BRDFs only makes sense if your entire pipeline is built for physical units - the extreme range of values can't be displayed properly without some form of tone mapping. You didn'...
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### The reciprocity of BRDF

You probably know that the BRDF is to calculate the reflected light, from a light source to a camera (In examples a light source and a camera is used, but it does not need to be just that). The ...
• 1,555
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• 23.7k

### PBR missing rim darkening on non metallic rough surfaces

The problem is in the diffuse term, which can be seen by making the specular portion of IBL not be added into the result. The diffuse only render will not have the darkening, and of course, the ...
• 7,331
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### Importance Sampling in Unreal Engine Formula Derivation (Irradiance term)

I just read notes on moving frostbite to pbr and I found the derivation of the method above. So I will just show the derivation here and quote some of the explanation. One can notice an extra〈n·l〉...
• 473
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### Iridescence/Thin-film interference integration as a layer

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 ...
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### Why can I see the diffuse lighting effect on a perfect mirror?

Dielectric materials (which is what you get when metalness is 0) don't exhibit a mirror-like effect. Think of a sheet of smooth, non-transparent plastic. Real-life mirrors are panes of glass or ...
• 872