Questions tagged [diffuse]

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22 votes
2 answers
7k views

How to properly combine the diffuse and specular terms?

As far as I understand, in a BRDF the Fresnel term is telling us the probability for a photon to be reflected or refracted when it hits a surface. The reflected photons will contribute to the ...
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10 votes
3 answers
2k views

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

So I been thinking about this for a while and tried to google for an answer but without any success. If all your textures are 8bit LDR images, like JPEGs, couldn't that potentially cause conflicts ...
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8 votes
2 answers
1k views

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

I am currently working with Earl Hammon Jr's Presentation PBR Diffuse Lighting for GGX+Smith Microsurfaces (now mentioned as [PBR, p.XYZ] and have read through (among others) Brent Burley's Physically-...
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  • 1,457
7 votes
1 answer
2k views

Intuitively understanding conservation of energy for the Lambertian BRDF

The Lambertian BRDF is defined as $R / \pi$, where the division by $\pi$ is there to maintain conservation of energy. The derivation is provided here. The maths makes sense, and I can understand ...
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6 votes
1 answer
358 views

Should not specular reflection on a rough surface be similar to diffuse reflection?

Different BRDFs are usually used to compute diffuse and specular reflection. Some of the most often used include for example the Lambert BRDF for diffuse reflection and the Cook-Torrance BRDF for ...
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  • 1,689
6 votes
1 answer
521 views

Derivation of Wikipedia's path tracing diffuse BRDF

Wikipedia's path tracing algorithm has the following line for the diffuse BRDF: Color BRDF = 2 * m.reflectance * cos_theta; I'm a little confused as I've been ...
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  • 700
5 votes
2 answers
141 views

Problem with Basic Diffuse Lighting

So recently I have been learning how to implement Diffuse Lighting in DirectX and I have done so with the following code: ...
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  • 2,413
5 votes
1 answer
154 views

Equivalent of Fresnel law for determining transmitted/diffuse split

I understand that Fresnel tells us what percentage of light reflects vs refracts, but what law tells me the percentage of refracted light that is transmitted versus the percentage of refracted light ...
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4 votes
0 answers
1k views

Better alternatives to the Lambert BRDF

After reading about the new Disney Diffuse BRDF, I have been wondering if this is currently the best Diffuse BRDF at the moment? How much more of a difference would this make compared to using a ...
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  • 2,413
3 votes
1 answer
111 views

Data fitting SVBRDF with L-M

I am reading two shot svbrdf capture . I want to understand the data fitting. For example, I have my input image 3000x2000 pixels, and I divide it to create my source tiles of 192x192 pixels. The way ...
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2 votes
2 answers
644 views

Diffuse lighting calculations in ray-tracer

I am trying to write a ray-tracer. The lighting part is proving to work but not accurately. To debug I simplified the scene to a single sphere centered at the origin with a radius of 1 and a point ...
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2 votes
0 answers
264 views

Exact Formula for Diffuse Hemisphere Lighting

The OpenGL Programming Guide states the formula for diffuse hemisphere lighting on a surface with normal vector $\vec{n}$ as $L_o(\vec{n}) = L_i(\uparrow) (1-\frac{1}{2}\sin(\theta)) + L_i(\downarrow)...
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1 vote
1 answer
89 views

Ray tracing Bug with Diffuse material

I am trying to do ray tracing in python (following the tutorial given in Ray Tracing in a weekend). Basically I am shooting rays from eye and the recursively bounce around, each time they hit ...
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  • 131
1 vote
1 answer
293 views

Confusion around Lambert's Cosine Law in Ray Tracing in One Weekend

Peter Shirely's Ray Tracing in One Weekend presents the following function to calculate the color of a lambertian material (See chapter's 7 and 8): ...
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1 vote
1 answer
146 views

question about true Lambertian reflection in Ray tracing in one weekend

I have a question about Peter Shirley's Ray tracing in one weekend. In the True Lambertian Reflection section, when talking about rejection method, he said This distribution scales by the cos^3(ϕ) ...
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  • 11
1 vote
1 answer
127 views

Specular reflection with different viewing direction where reflection direction and viewing direction coincide

Suppose $P_1$ and $P_2$ two different points on surface. And let $l$: be the light source direction, $n$: normal vector $r$: specular reflection direction $v$: viewing direction . In case 1 (at $P_1$...
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1 vote
0 answers
49 views

Contour-line looking artifact on diffuse irradiance map

I tried implementing my own diffuse irradiance map maker after reading Learn OpenGL > PBR > IBL > Diffuse Irradiance. It takes an HDR image and makes six HDR cube map. But It keeps making ...
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1 vote
0 answers
63 views

Oren-Nayar Reflectance

I'm trying to implement Oren-Nayar reflectance and I don't quite understand the Wikipedia article on it. In the article, it has this diagram: I can't figure out what $(\theta_i, \phi_i)$ and $(\...
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  • 111
1 vote
0 answers
84 views

How to automatically project texture from high poly mesh to low poly mesh?

I have two aligned meshes: I have exact mapping from each vertex of low poly mesh to surface of a high poly mesh. High poly (~100K vertices) mesh is non-manifold, low poly (~1K vertices) is manifold ...
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  • 151
0 votes
1 answer
79 views

OpenGL old-style diffuse shading producing unexpected effects

Question: What is going wrong with the shape of the contours of constant illumination in the below picture ? Detail: Although Lambertian shading might be ill-regarded because it exposes the hard edges ...
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  • 169
0 votes
1 answer
141 views

Factor of 2 converting radiance to irradiance

For a Lambertian surface, the radiance at a point is $$L = \frac{\alpha}{\pi}\cos\theta_i E_0$$ If we have an infinite flat surface, albedo = 1, illuminated directly normal, then we get $$L = \...
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0 votes
0 answers
52 views

Ray tracing of a diffuse material sphere doesn't work, the sphere just shades black

I made this ray tracer in javascript to run on html with imageData. I have been using the book "Ray Tracing in One Weekend" as a reference (https://raytracing.github.io/books/...
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0 votes
0 answers
27 views

How to measure the reflectance of a material without using a Spectralon

I am trying to measure the reflectance% of a surface (it is made of Teflon and is very white). I am using a line spectrometer. I believe the piece can replace an expensive Spectralon for some ...
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0 votes
1 answer
117 views

Ringlike artifacts produced by rays bouncing off a light source

I recently set up a (very basic) ray-marched path-tracer, and I'm getting strange surface patterns on my area light [link]. I'm using known-valid analytical normals for the light's surface, and the ...
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