LuxCoreRender Forums

I don't know how the Metropolis algorithm chooses its generated Random numbers. Actually if it works with a seed number it should always produce the same series of generated random numbers. A developer should be able to check this.

Did you already check if your scene contains lamps with many emissive triangles?
Maybe it helps a lot regarding reproducible renders if you normalize Importance for each lamp. This means to divide 1 by the number of light sources (amount of triangle s of an object). The default lights like spot or point get an Importance of 1; the area lamp gets an Importance of 0.5 (it has two tingles); objects with an emissive Material get 1/numberoftriangles.

However this approach may need a lot of samples to converge.. but does it anyway if there are many lights in a scene.

The kind of light also is important, if you want comparable brightness define lights as physics not as artistics. I prefer to define brightness of lamps in lumen.

EDIT (facts you probably know well)
Another big influence on the brightness of light is its area.
A further influence is the maximal angle a light emits its rays.

FarbigeWelt wrote: Tue Jul 01, 2025 8:17 am I don't know how the Metropolis algorithm chooses its generated Random numbers. Actually if it works with a seed number it should always produce the same series of generated random numbers. A developer should be able to check this.

Did you already check if your scene contains lamps with many emissive triangles?
Maybe it helps a lot regarding reproducible renders if you normalize Importance for each lamp. This means to divide 1 by the number of light sources (amount of triangle s of an object). The default lights like spot or point get an Importance of 1; the area lamp gets an Importance of 0.5 (it has two tingles); objects with an emissive Material get 1/numberoftriangles.

However this approach may need a lot of samples to converge.. but does it anyway if there are many lights in a scene.

Yes, our scenes often contain objects with lots of emissive triangles. This is one of th reasons why we stick on bidir, because it normally handles millions of emissive triangles + caustics and so on without any issues. Tomorrow i revise the light importance idea but it seems to me something which sould be in charge of bidir+metropolis.

FarbigeWelt wrote: Tue Jul 01, 2025 10:46 am The kind of light also is important, if you want comparable brightness define lights as physics not as artistics. I prefer to define brightness of lamps in lumen.

EDIT (facts you probably know well)
Another big influence on the brightness of light is its area.
A further influence is the maximal angle a light emits its rays.

Yes, we use only lifelike values for emitters and even for the sky. We did a series empiric measurements of sky and sun intensites at different hours and conditions and used that data to set-up our scenes. All matched with film sensitivity lenses luminosity and all that stuff. Regarding the brightness of the light related to the area of the amitting surface, this should be only in case if you use Lux variables insted of Lumen values, or not?

daros wrote: Tue Jul 01, 2025 3:26 pm
Regarding the brightness of the light related to the area of the amitting surface, this should be only in case if you use Lux variables insted of Lumen values, or not?

Indeed Lux could be the better choice for complex lights.

1 Lx = 1 Lm/m^2

This means Lux are area normalized Lumen.

FarbigeWelt wrote: Tue Jul 01, 2025 6:37 pm
Indeed Lux could be the better choice for complex lights.

1 Lx = 1 Lm/m^2

This means Lux are area normalized Lumen.

But there isn't any such choice in BlendLuxCore ..

daros wrote: Tue Jul 01, 2025 3:18 pm
Yes, our scenes often contain objects with lots of emissive triangles. This is one of th reasons why we stick on bidir, because it normally handles millions of emissive triangles + caustics and so on without any issues.

Tomorrow i revise the light importance idea but it seems to me something which sould be in charge of bidir+metropolis.

4 Different Lights:
Point Lamp: SubDiv 0, "Tris" 2, Importance 0.5
Ico Sphere: SubDiv 1, Tris 20, Importance 1.0
Ico Sphere: SubDiv 2, Tris 80, Importance 1.0
Ico Sphere: SubDiv 3, Tris 320, Importance 1.0

Matte.White.Emit.Importance.1


Noise patterns of indirect lightening depending on Metropolis' Settings.
(part one)

Noise patterns of indirect lightening depending on Metropolis' Settings.
(part two)

To test temporally stability of BiDir Metropolis renders I set up a scene with to different Spot lights. One spot is the built in light, another contains a half Icosphere with emissive Matte material. The Icosphere points inward an open half sphere with Material Mirror. All light from this complex spot is indirect. In two videos only Camera moves. In the other videos the spot light moves too. An empty vine glass throws caustics on floor and/or a wall.
One video shows both types of spots with an Importance of 1 for both laps. As expected the default spot(right) renders noisier than the complex spot (left) with 160 emissive faces. For other videos showing both spots, the default Spot's Importance is set to 80.

Unfortunately the rather small and noisy videos (32 Samples per Frame) loos a lot of their quality uploaded to youtube. Does anybody have a tip for me where to upload the videos for sharing in full quality?

Empty Glass in default Spot light
Moving Camera targeted to empty glass
Empty Glass in modeled Spot light with 160 emitting faces and lampshade
Moving Camera targeted between the two Spots

Modelled in Blender 4.2.11
Rendered with BlendLuxCore 2.10.0

Metropolis 50pc, 1024, 50pc Anim, Cam, Spot
https://youtube.com/shorts/EiDsjPYmSHU

Metropolis 50pc, 1024, 50pc Anim, Cam and complex Lamp
https://youtube.com/shorts/WejGD8Pp0UI

Metropolis 50pc, 1024, 50pc Anim, Cam
https://youtube.com/shorts/d0azizFzVzo

Metropolis 50pc, 1024, 50pc Anim, Cam complex Spot light
https://youtube.com/shorts/6LWnhymypds

Metropolis 40pc, 512, 10pc Anim, Cam, Lamps
https://youtu.be/IIzDZ229FdU

#Caustics and Shadows of an empty vine #Glass depending on Spot light's type

The Blue Spot light throws indirect light only. It's lamp shade is an open half sphere mirroring light of a half Iso sphere emitting light inwards.
The Yellow Spot light is a default Blender / #LuxCore light.
The #performance/#importance of the default spot is set to 60 to achieve a comparable #lightning effect.

Modeled in #Blender 4.2.11
Rendered with #BlendLuxCore 2.10.0

Temporally stability of #BiDir, #Metropolis Sampler, 8 Samples per Frame, denoiser #OIDN
https://youtu.be/cMocmy6d_XI

Temporally stability of #BiDir, #Metropolis Sampler, 32 Samples per Frame, denoiser #OIDN
https://youtu.be/spIjLNHKEUs