Lighting and PBR - The Parthenon

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JuandeLara
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Lighting and PBR - The Parthenon

Post by JuandeLara » Wed Oct 28, 2020 3:14 pm

Hello everybody,
I am new using Luxcore, but it looks pretty powerful. The reason I have chosen this renderer is that it appears to be one of the most accurates when it comes to replicating lighting (PBR).

I am undertaking a PhD that aims to replicate the light inside the Parthenon. It is believed that a pool of water made the rays of the sun bounce and better illuminate the statue inside.

In the process I had a couple of doubts, when it comes to illuminate an interior (where I need to observe the light rays admitted).
- The scene has been setup with Engine as Bidir and the Sampler as Metropolis. (as the pool of water in the ground works as a mirror). View transform is Filmic. Pixel effect is Mitchell.
- The world , I have set up the light as Sky. Here my issue is undersanding "Gain" whitin the remit of PBR. My scene looks pretty with a gain of 3.0 But what does that mean exactly? Is that a real replica of the sun intensity (lux)?
- Then my Sun (light) has been setup with a gain of 3.0 as well and an exposure of 0.0

With these settings, the scene looks "pretty" but, my thoughts are that "the interior is too dark"....is this believe true? Because I wonder how can I better calculate my gain values so that it replicates the real value of light in real world? Sorry if this does not make much sense...

I attach a couple of images to explain what I am talking about, and one of the general scene, how it is

-In terms of materials: If I wanted all surfaces to be as closer as possible to marble, in terms of reflection (glossiness), what is the best way to do so? Are there any libraries of materials that have been developed to be PB?

THank you so much!

https://i.ibb.co/JRPBVDh/Lux-Core-FOrum.jpg
https://i.ibb.co/7Sxwg2x/Lux-Core-FOrum2.jpg

chafouin
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Re: Lighting and PBR - The Parthenon

Post by chafouin » Wed Oct 28, 2020 5:10 pm

Using the physical sun and sky, the default values with a Gain of 1 are physically based.
If it's too dark inside, you need to adjust your camera exposure to compensate for that.

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Sharlybg
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Re: Lighting and PBR - The Parthenon

Post by Sharlybg » Wed Oct 28, 2020 5:22 pm

chafouin wrote:
Wed Oct 28, 2020 5:10 pm
Using the physical sun and sky, the default values with a Gain of 1 are physically based.
If it's too dark inside, you need to adjust your camera exposure to compensate for that.
Please tell me are Lux camera setting same as real world camera ?
In my test it seem way more dark.
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JuandeLara
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Re: Lighting and PBR - The Parthenon

Post by JuandeLara » Thu Oct 29, 2020 10:20 am

Yes that worked. Thanks.

Do you know if in an scene like this, I can create volumetric lights? Is it the same process as here viewtopic.php?f=4&t=1230#p14712? can I hide the box?

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B.Y.O.B.
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Re: Lighting and PBR - The Parthenon

Post by B.Y.O.B. » Thu Oct 29, 2020 10:26 am

In your setup you will need a mesh (e.g. fog box) to limit the extent of the fog, because you're using lights that are infinitely far away (sun and sky) and you don't want to have an infinite amount of fog between them and your geometry.
So just use the procedure described here: viewtopic.php?f=3&t=2697#p25955
(Scene enclosed in box with null material and internal homogeneous volume, same volume also set as camera volume).
some more details: viewtopic.php?f=3&t=2697#p26003

JuandeLara
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Re: Lighting and PBR - The Parthenon

Post by JuandeLara » Thu Oct 29, 2020 11:35 am

Hi B.Y.O.B! Thank you, I originally followed this video tutorial: https://www.youtube.com/watch?v=PrHWwH_ ... u.be&t=356

DId not work. So I did what you suggested, null box, interior volume called 'dust', and then camera with volume dust. Still not working.

I have uploaded the scene and wondered if you could please have a look and tell me what the heck I am doing wrong? :ugeek: :?


http://www.archaeological-reconstructio ... ation5.zip

chafouin
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Re: Lighting and PBR - The Parthenon

Post by chafouin » Fri Oct 30, 2020 7:10 am

Sharlybg wrote:
Wed Oct 28, 2020 5:22 pm
Please tell me are Lux camera setting same as real world camera ?
In my test it seem way more dark.
Unless something changed, camera settings are correct, except for a weird issue that actually makes it brighter than it should (discussed here: viewtopic.php?f=4&t=1601&hilit=lumen&start=70)

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Sharlybg
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Re: Lighting and PBR - The Parthenon

Post by Sharlybg » Fri Oct 30, 2020 9:07 am

chafouin wrote:
Fri Oct 30, 2020 7:10 am
Sharlybg wrote:
Wed Oct 28, 2020 5:22 pm
Please tell me are Lux camera setting same as real world camera ?
In my test it seem way more dark.
Unless something changed, camera settings are correct, except for a weird issue that actually makes it brighter than it should (discussed here: viewtopic.php?f=4&t=1601&hilit=lumen&start=70)
Thnaks for your answer. Will do more test.
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B.Y.O.B.
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Re: Lighting and PBR - The Parthenon

Post by B.Y.O.B. » Fri Oct 30, 2020 1:46 pm

Your scattering scale was set to 0.
It is a multiplier for the scattering color:
total scattering = scattering color * scattering scale.
So setting it to 0 disables any scattering.

Just use a higher number like 0.1:
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JuandeLara
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Re: Lighting and PBR - The Parthenon

Post by JuandeLara » Fri Oct 30, 2020 5:26 pm

B.Y.O.B. wrote:
Fri Oct 30, 2020 1:46 pm
Your scattering scale was set to 0.
It is a multiplier for the scattering color:
total scattering = scattering color * scattering scale.
So setting it to 0 disables any scattering.

Just use a higher number like 0.1:
Ogh, thank you. I swear I tried this! but I might have given a value that was too high. Thank you so much!

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