16 votes
Accepted

Why does graphics speak of "dielectrics" rather than insulators?

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 ...
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15 votes
Accepted

Why do most photorealistic renderers have similar material test scenes?

While teapot, spheres and trusty Suzanne are not per se bad test scenes for materials, here are some things to consider. You can apply them to said examples to forge your own opinion. First and ...
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  • 2,223
9 votes

Why do most photorealistic renderers have similar material test scenes?

You can choose whatever you want offcourse. A good material sample ideally has a few properties. It needs to show how the light falls of as the angle between light and surface normal changes. A ...
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  • 8,169
7 votes
Accepted

How can a diffused(frosted) glass be modelled in path tracing

Assuming that you are familiar with the concept of BSDFs, the usual way of modelling rough dielectric surfaces (i.e. glass, water, plastics) is to use microfacet-based models like Microfacet Models ...
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  • 1,377
7 votes

What is the difference between glossy and specular reflection?

The charts you show aren't showing two different phenomena - "glossy reflection" and "specular reflection" - they're showing two parameters of specular reflection. One is the specularity or specular ...
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  • 6,450
7 votes
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Path tracer - multi layered materials and importance sampling

Wenzel Jakob et al presented a framework for layered Materials at SIGGRAPH 2014. Section 6.2 explains importance sampling. If you prefer code over equations, the method is implemented in the Mitsuba ...
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5 votes
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Is there a material that contributes to GI, but isn't directly visible?

You can use single sided triangles for the ceiling so that they are pointing towards the room. This way the ceiling influences the GI in the room but you can see through it when observing from outside
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  • 3,556
5 votes
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Phong: Real-time rendering of Metal and Plastic Materials

Diffuse colours on materials typically come from within the material, while the specular colour is from the very surface. Coloured plastic materials are made by embedding particles of dye inside a ...
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  • 6,450
4 votes
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Mimicking Blender's "roughness" in my path tracer

For explicit light sampling: yep, you just evaluate the BRDF for that incoming direction and the output direction back toward the camera. There's probability involved in the case of an area light: you ...
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4 votes

What is the most physically accurate model of surface materials possible in computer graphics?

BRDFs are not accurate for any dielectric surface, as all of them have some degree of subsurface scattering. A BSSRDF is also just an approximation based on the assumption of a semi-infinite slab. ...
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4 votes

Examples of anisotropic surfaces

A really common case in the real world are industrially fabricated metal surfaces which often contain patterns (due to their creation process) with strongly anisotropic surface distributions, ...
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  • 161
3 votes
Accepted

Examples of anisotropic surfaces

Most manufactured items that are made by grinder, milling, shaper or lathe that have not been polished. Due to tiny grooves caused by the cutting head. Intentionally brushed surfaces. Mainly to make ...
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  • 8,169
3 votes
Accepted

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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3 votes

How can I implement this BSDF?

When implementing transmission into a path tracer you have to keep in mind that neither BRDF's nor your previous sampling method are gonna cut it. You will need to think about what happens to light on ...
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3 votes
Accepted

Does light particle loses energy when it hits something?

Both of your two proposed solutions are valid, with different properties. Which you choose is purely a design issue. The difference is that your probabilistic rays/particles (1) don't need to store ...
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  • 6,450
2 votes
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Material Layering

It would be too expensive (both performance and memory wise) to evaluate BRDF first for each material layer and then blend the layers. Thus the material layer parameters & textures are rather ...
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  • 3,556
2 votes

Loading a material via assimp

AI_MATKEY_COLOR_TRANSPARENT is used to define the transparent colour and AI_MATKEY_REFRACTI is the refractive index.
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  • 2,244
2 votes

Why does graphics speak of "dielectrics" rather than insulators?

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 ...
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2 votes

What is the difference between glossy and specular reflection?

Gloss and Specularity are features of the surface. In modern PBR terms we usually refer to the smoothness and metalness of a surface instead (unless you use a specular workflow, then metalness is ...
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1 vote
Accepted

Converting from RGB Color Picker to Surface Reflectance

Yes, I think you're right. The values from a typical color picker would be in a gamma encoding or sRGB encoding and would need to be converted to linear to use as reflectance. This is probably just a ...
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1 vote

How to read illum value from mtl file using Assimp library?

According to the source (https://github.com/assimp/assimp/blob/b7df376836e36c4b6998ce95d97626e30f61c2f0/code/AssetLib/Obj/ObjFileImporter.cpp#L594) only illum values of 0, 1, 2 are supported: ...
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  • 111
1 vote
Accepted

Microfacet BRDF artifacts

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:
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  • 188
1 vote
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Confused on reflection coeffcient of Fresnel equations

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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1 vote
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Understanding material .mtl files

@PaulHK explained it very well in the comment section: Ambient is a (rough) approximation of indirect lighting. For example, an outdoor object would be lit by the sun but the surfaces facing away ...
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1 vote

Combine material coefficients and textures in Phong Shading

When applying various types of attenuation you are just multiplying by some number smaller than 1. This is akin to every atom of your material having some probability of absorbing the light that hits ...
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1 vote
Accepted

Confused about material layering

There is no single method of layering materials. Some implementations, as you have observed, simply interpolate shader input parameters. This helps especially in contexts where code divergence comes ...
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1 vote

Phong: Real-time rendering of Metal and Plastic Materials

https://courses.cs.washington.edu/courses/cse458/99sp/projects/help/phong_params.html ...
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