Hello all,
SO basically I am trying to obtain the most reliable and PBR behavior of alight in a complex 3D space, reason why I chose LuxCore. I have set up a scene and I am calculating the sun behavior in it as obtained with external data for sun positioning. However when setting the renderer I have some questions.
I am using Bidir - Metropolis.
For the best possible result in terms of behavior of light, is it fair to say that 'Light PAths>Max Bounces> Eye Depth and Light Depth should be set at the highest values (for example 800). I attach a test in between that value at 10 vs. that value at 800. The result is that the interior is better lit (the walls are a glossy type of material to replciate marble). Is this rationale correct? Is the value 800 a more accurate representation of real live light behaviour?
Thanks!
doubts
Bidir - Metropolis.
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Please upload a testscene that allows developers to reproduce the problem, and attach some images.
Please upload a testscene that allows developers to reproduce the problem, and attach some images.
Re: Bidir - Metropolis.
Hi,
yes, in general a higher path depth is better, just your example of 800 is very excessive for almost all realistic scenarios. Let me give you some example numbers:
First off, you can find an example of a situation requiring >100 describes in the follwing thread: viewtopic.php?f=4&t=2667. This scenario is based on multiple total internal reflection in a glass or acrylic material.
For other surfaces, it depends on the reflectivity. A really good white paint could reach up to, lets say, 0.9 total reflectance. If you bounce that between 10 surfaces it becomes 0.9^10 = 0.35. So after 10 bounces it still carries 35% the energy, which can be significant. after 50 bounces it is down to 0.9^50 = 0.005. Without cosnidering HDR images or gamma correction, this is approximately one step in an 8-bit png or jpg image (1/255 = 0.004).
If your scene contains also darker materials, your average relfectance will be maybe 0.7. with 10 bounces this becomes 0.7^10 = 0.028. So still a possible contribution by higher path depths, but not too much.
You have only provided an image, and not a .blend file that shows all material setups, so hard to say what should be expected for your setup.
yes, in general a higher path depth is better, just your example of 800 is very excessive for almost all realistic scenarios. Let me give you some example numbers:
First off, you can find an example of a situation requiring >100 describes in the follwing thread: viewtopic.php?f=4&t=2667. This scenario is based on multiple total internal reflection in a glass or acrylic material.
For other surfaces, it depends on the reflectivity. A really good white paint could reach up to, lets say, 0.9 total reflectance. If you bounce that between 10 surfaces it becomes 0.9^10 = 0.35. So after 10 bounces it still carries 35% the energy, which can be significant. after 50 bounces it is down to 0.9^50 = 0.005. Without cosnidering HDR images or gamma correction, this is approximately one step in an 8-bit png or jpg image (1/255 = 0.004).
If your scene contains also darker materials, your average relfectance will be maybe 0.7. with 10 bounces this becomes 0.7^10 = 0.028. So still a possible contribution by higher path depths, but not too much.
You have only provided an image, and not a .blend file that shows all material setups, so hard to say what should be expected for your setup.
Re: Bidir - Metropolis.
800 is an over the sky value, you are still using floating point 32bit precision, it is like an order of magnitude more than a very high value.
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Re: Bidir - Metropolis.
Oh I see. Thanks for this info. So I think I am just being very lame with this and not understanding some material processes at all.CodeHD wrote: ↑Thu Dec 17, 2020 3:41 pm Hi,
yes, in general a higher path depth is better, just your example of 800 is very excessive for almost all realistic scenarios. Let me give you some example numbers:
First off, you can find an example of a situation requiring >100 describes in the follwing thread: viewtopic.php?f=4&t=2667. This scenario is based on multiple total internal reflection in a glass or acrylic material.
For other surfaces, it depends on the reflectivity. A really good white paint could reach up to, lets say, 0.9 total reflectance. If you bounce that between 10 surfaces it becomes 0.9^10 = 0.35. So after 10 bounces it still carries 35% the energy, which can be significant. after 50 bounces it is down to 0.9^50 = 0.005. Without considering HDR images or gamma correction, this is approximately one step in an 8-bit png or jpg image (1/255 = 0.004).
If your scene contains also darker materials, your average relfectance will be maybe 0.7. with 10 bounces this becomes 0.7^10 = 0.028. So still a possible contribution by higher path depths, but not too much.
You have only provided an image, and not a .blend file that shows all material setups, so hard to say what should be expected for your setup.
Basically, lets assume the whole scenario is built in marble. I have estimated the marble as the attached material. How did I do this estimation? Well by eye, which is not very scientific. Is my starting point (setting a glossy material for it) correct? I estimated the roughness to be 0.1, which I guess is the reflectance? I would say the current setup looks "like marble"....Is there anywhere we the reflectance value for a material like gold or marble can be sourced? Am I missing an important point here?
I think I need to go back to some material basics. For example I don't know what Absorption depth stands in this context.
Would then the Max bounces at 30 be proper for such scenario?
Re: Bidir - Metropolis.
There is no attachment, did you forget it?JuandeLara wrote: ↑Thu Dec 17, 2020 4:37 pm Basically, lets assume the whole scenario is built in marble. I have estimated the marble as the attached material.
Yes and no. Marble usually has subsurface scattering so you would rather need glossy translucent and a homogeneous volume.JuandeLara wrote: ↑Thu Dec 17, 2020 4:37 pm Is my starting point (setting a glossy material for it) correct?
No, reflectance would be the color setting.JuandeLara wrote: ↑Thu Dec 17, 2020 4:37 pm I estimated the roughness to be 0.1, which I guess is the reflectance?
Roughness just tells you if the surface scatters more like a mirror (ray bounces off at the same angle as it is incoming), or like a diffuse surface (ray bounces in a random direction regardless of where it comes from).
Now, roughness can reduce the reflectance depending on the rougness model, but that's an issue of the algorithms used, not the real-world physics behind it.
I'm not sure of a database right now. Perhaps someone else can help. Marble is a natural material, so there can be variations of course. It all depends on what your goal is. Artistic; replicating an existing room; predicting a building to be constructed; ...JuandeLara wrote: ↑Thu Dec 17, 2020 4:37 pm I would say the current setup looks "like marble"....Is there anywhere we the reflectance value for a material like gold or marble can be sourced? Am I missing an important point here?
Yeah, most of the time that will be fine.JuandeLara wrote: ↑Thu Dec 17, 2020 4:37 pm I think I need to go back to some material basics. For example I don't know what Absorption depth stands in this context.
Would then the Max bounces at 30 be proper for such scenario?
One more detail to add since you talk about BiDir: The total path depth can be as high as the sum of eye depth and light depth! So even 15+15 would be a lot. It can be very scene dependent what you really need, depending on the involvement of caustics.