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14 votes
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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 ...
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9 votes
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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 '...
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9 votes
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Should not specular reflection on a rough surface be similar to diffuse reflection?

No, because the underlying physics is not the same, nor the lobe shape - not to speak of their parameters such as color and Fresnel term. Specular is really true surface interaction with the ...
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8 votes

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. ...
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8 votes

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 ...
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6 votes
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Derivation of Wikipedia's path tracing diffuse BRDF

When you perform regular Monte Carlo integration over a hemisphere using $N$ samples, each sample represents $\frac{2\pi}{N}$ steradians. So the Monte Carlo integration for Lambertian BRDF is: $$\...
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6 votes
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Why is the half vector not used in diffuse BRDF Fresnel calculations?

I finally figured out a flaw in my argumentation to use the half vector for the diffuse part. tl;dr version: $\alpha_{hi}$ and $\alpha_{ho}$ are not equal, this assumption only works for the specular ...
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  • 1,457
5 votes

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

I'd like to invite readers to read this article about Quake 2 engine rasterization technology explained in details, if they have the time. If TLDR, please pay attention to this image: What we see is ...
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  • 613
5 votes
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Intuitively understanding conservation of energy for the Lambertian BRDF

A perfect Lambert reflector actually reflects light in a cosine distribution - that is, the amount of light per unit area reflected in any given direction $R$ is proportional to $N \cdot R$. The ...
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  • 2,302
4 votes

Diffuse lighting calculations in ray-tracer

Some elementary trigonometry tells you what to expect from this situation. The angle to see the shadow terminator is marked on the diagram, and a use of SOHCAHTOA tells you it's $\cos^{-1}\tfrac{1}{2}...
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3 votes

Problem with Basic Diffuse Lighting

Your ambient lighting contribution is missing from the second one (:
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  • 7,361
2 votes

Equivalent of Fresnel law for determining transmitted/diffuse split

Physically, the origin of diffuse light is subsurface scattering, which happens continuously as light travels through a material. So, the proportion of transmitted light depends on the thickness of ...
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2 votes

Why is the half vector not used in diffuse BRDF Fresnel calculations?

We're actually going through that paper for our own GGX BRDF metallic & edge_tint model, and we've spotted one crucial problem. Hammon is still using the Fresnel Schlick approximation for his ...
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2 votes
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Ray tracing Bug with Diffuse material

I see a couple of problems by scanning quickly over your code. You are using ray.origin as new origin when scattering the ray off the surface, you should however use the hit point as origin of the ...
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2 votes
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Confusion around Lambert's Cosine Law in Ray Tracing in One Weekend

It is cancelled out by the probability density function in the estimator. The pdf in their case is exactly: $\frac{\cos\theta}{\pi}$, which is in the denominator: ...
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1 vote
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OpenGL old-style diffuse shading producing unexpected effects

As far as I remember, without a fragment shader the shading is only evaluated at vertices then interpolated. Try subdividing the mesh.
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1 vote

question about true Lambertian reflection in Ray tracing in one weekend

There are two different methods of computing a random ray bounce being compared in this section of the online book, the first one is: Pick a point $s$ anywhere inside the sphere, then compute a vector ...
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  • 2,132
1 vote
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Factor of 2 converting radiance to irradiance

I don't really understand what are you doing. I think your first equation shouldn't have a cos factor in it. We have the relation, $BRDF = dL_r / dE_i$ That is the brdf is the ratio of reflected ...
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1 vote

Problem with Basic Diffuse Lighting

...
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  • 2,433
1 vote

Data fitting SVBRDF with L-M

I read that paper as well last year. There's a strong assumption made by authors which is the "stationary". What this means is that in absence of light in given 3000x2000 pixels image the material is ...
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