PhotonGI caustics

[LuxNoob]

Hi everyone,

When using path+sobol and phontongi enabled, I get small circles instead of caustics. It only happens when viewed through glass (or water). If I put the camera behind water, caustics will render just fine. Also it works in bidr+metropolis.

I tried changing lookup radius, but I believe it didn't helped much.

Please see attachment for comparisons and more info.
HDRI can be downloaded at https://hdrihaven.com/hdri/?h=spiaggia_di_mondello

Thanks in advance!

[B.Y.O.B.]

You don't need env. light cache and indirect light cache in this scene.

About the caustics cache, you just need a lower lookup radius (and maybe raise max. size and lower step samples to focus more on the caustics, since they are taking more time to clear than the other noise).

[LuxNoob]

Thanks B.Y.O.B. a lot.

While its much more clean, small circles still appear in image, at least compared to bidr+metropolis.
Will they disapear with more samples?

And why does it only happens when seeing through glass?


Again thanks a lot for support!

[Dade]

Will they disapear with more samples?

Yes, if you have periodic cache update, more and more small circles (photon splashes) will overlap until the point you can not more see them.

And why does it only happens when seeing through glass?

If you have light tracing enabled (as you should), the cache is used only for for SDS paths (Specular-Diffuse-Specular paths, i.e. caustics seen trough specular objects), something not even BiDir+Metropolis can render.

[LuxNoob]

Thanks Dade for the quick answer.

However I didn't understand a thing:

If you have light tracing enabled (as you should), the cache is used only for for SDS paths (Specular-Diffuse-Specular paths, i.e. caustics seen trough specular objects), something not even BiDir+Metropolis can render.

If BiDir+Metropolis cannot render SDS paths, then how are caustics perfectly visible (and with very much less noise) using that?
(sorry if it is a stupid question but Im kinda new to photorealism)

PS: Is it possible if you Luxcore people join forces with blender team in order to have this amazing render engine integrated in blender by default?

Again thanks!

[Dade]

However I didn't understand a thing:

If you have light tracing enabled (as you should), the cache is used only for for SDS paths (Specular-Diffuse-Specular paths, i.e. caustics seen trough specular objects), something not even BiDir+Metropolis can render.

If BiDir+Metropolis cannot render SDS paths, then how are caustics perfectly visible (and with very much less noise) using that?
(sorry if it is a stupid question but Im kinda new to photorealism)

I haven't looked into the scene (have you enabled light tracing ?) but from your description, I was assuming they were SDS paths.

In this test scene, the caustics on the mirror are SDS paths and are visible when using caustic cache:

They are not visible if you use BiDir+Metropolis:

PS: Is it possible if you Luxcore people join forces with blender team in order to have this amazing render engine integrated in blender by default?

How could it be a viable option ? Aside from throwing LuxCore out of the window and just all working on Cycles ?

You know that has been, somewhat, tried in the past ... a story very few know

[LuxNoob]

have you enabled light tracing ?

Yes I did.

I haven't looked into the scene (have you enabled light tracing ?) but from your description, I was assuming they were SDS paths.

In this test scene, the caustics on the mirror are SDS paths and are visible when using caustic cache:

Well I'm not sure if they are SDS caustics, but my scene has the camera above the water, with caustics at the sand (camera is not underwater, but caustics are).

In your example with mirrors, you are saying I can only get the same results using the caustic cache (not using metropolis)?

About the caustics cache, you just need a lower lookup radius (and maybe raise max. size and lower step samples to focus more on the caustics, since they are taking more time to clear than the other noise).

Finally, I did what B.Y.O.B. told me, but in final render caustics are kind of "blurry" (not sharp) compared to BiDir+metropolis, though much better than before:

Thanks everyone for support!

[B.Y.O.B.]

Well I'm not sure if they are SDS caustics, but my scene has the camera above the water, with caustics at the sand (camera is not underwater, but caustics are).

They are SDS caustics, but since the only light in the scene is the environment light with HDRI, Bidir can render them (inefficiently), because environment lights are intersectible (I think). If you would use a non-intersectible light like a point or spot light, Bidir would not be able to render them.

Attached is an example:

test (1)_spot.blend

(878.62 KiB) Downloaded 207 times

bidir

caustic cache

Finally, I did what B.Y.O.B. told me, but in final render caustics are kind of "blurry" (not sharp)

Have you tried lowering the radius further?
Unfortunately it is an annoying trial&error process until you have figured out a good radius.

[Dade]

Well I'm not sure if they are SDS caustics, but my scene has the camera above the water, with caustics at the sand (camera is not underwater, but caustics are).

Yes, they are SDS paths: Delta Light => Water (S) => Sand (D) => Water (S) => Eye.

In your example with mirrors, you are saying I can only get the same results using the caustic cache (not using metropolis)?

Yup.

You can not. Try to render your scene with a point light source (i.e. a delta light source) instead of an HDR and you will see that there will be not caustics under water.

[LuxNoob]

Thanks Dade and B.Y.O.B.,

Your kind and quick answers allowed me to understand deeper how LuxCore handles caustics.

Regards,
a proud luxcore user.