Some thoughts on Caustics

[Njen]

Just to chime in here on a request about caustics that has already been asked for, is the ability to enable caustics by material is necessary. For example, caustics really makes eyes look much more realistic, but I don't want to turn on caustics for the entire scene just to get a few pixels looking better.

The current work around I am doing is rendering a second pass of just the eyes held out by the rest of the scene, then comping the caustics render element from that second pass on top of my character render. The final result looks great and takes less time than if I had enabled caustics for the whole scene, but there is obviously the overhead of rendering a second pass to get what I want.

[Javadevil]

1) upgrade your CPU to double # of cores (e.g. new ryzens with 16 cores costing $750)
2) turn on caustics in every render
3) render time stays the same, every scene has caustics
4) you got caustics for $750 ;)

Thats my plan :)

[Ondra]

Just to chime in here on a request about caustics that has already been asked for, is the ability to enable caustics by material is necessary. For example, caustics really makes eyes look much more realistic, but I don't want to turn on caustics for the entire scene just to get a few pixels looking better.

The current work around I am doing is rendering a second pass of just the eyes held out by the rest of the scene, then comping the caustics render element from that second pass on top of my character render. The final result looks great and takes less time than if I had enabled caustics for the whole scene, but there is obviously the overhead of rendering a second pass to get what I want.

The way the current solver works, there probably wouldnt be the speedup you would expect from this, since the photons cannot be guided to hit just specific materials...

[Jpjapers]

The way the current solver works, there probably wouldnt be the speedup you would expect from this, since the photons cannot be guided to hit just specific materials...

Just curious. Do you emit special photons for the caustics that behave differently or do you use the same photons but run different calculations. Just curious about how it works :)

[Juraj]

I will just put this small trick out here for desperate people: Render Caustics outside of beauty pass, and denoise them. Even Optix Denoiser creates magic out of them in matter of minutes.

[Ondra]

The way the current solver works, there probably wouldnt be the speedup you would expect from this, since the photons cannot be guided to hit just specific materials...

Just curious. Do you emit special photons for the caustics that behave differently or do you use the same photons but run different calculations. Just curious about how it works :)

we use photons only for caustics, not for anything else. Hope I understrood the question right ;)

[Mr.Max]

what about adding Caching option for caustics  ?
In VRay we used to calculate the caustics once then use the same cache for all other shots, when there is no animation of course .
is is possible to add in future?

[martinsik]

what about adding Caching option for caustics  ?
In VRay we used to calculate the caustics once then use the same cache for all other shots, when there is no animation of course .
is is possible to add in future?

Such caching would be extremely memory consuming. Corona caustics solver generates a new set of photons for each pass with each set having millions of photons. Let's say you render 100 passes per image, the cache would then contain photons from all the passes, so something around billion photons. This would hardly fit into memory.

[shoebu23]

Team,

Amazing job, well done!  Quick question... with 'only in caustics element enabled', is there a way to see the combined effect directly in the VFB without having to go into Photoshop?  I like the idea of separating out beauty from CShading_Caustics- but would love to be able to quickly see (or even adjust) it in the VFB.  Thanks!

[TomG]

Team,

Amazing job, well done!  Quick question... with 'only in caustics element enabled', is there a way to see the combined effect directly in the VFB without having to go into Photoshop?  I like the idea of separating out beauty from CShading_Caustics- but would love to be able to quickly see (or even adjust) it in the VFB.  Thanks!

No way to do this at present, no, sorry.

[Juraj]

There is one workaround, I will write it just for the sheer absurdity :- ).

Make two copies of the same light (one with Caustic On, one Off), each into separate LightSelect Layers and than you can see both Beauty+Caustic and Beauty without in LightMixer.

[Ondra]

There is one workaround, I will write it just for the sheer absurdity :- ).

Make two copies of the same light (one with Caustic On, one Off), each into separate LightSelect Layers and than you can see both Beauty+Caustic and Beauty without in LightMixer.

please don't ;)

[Ondra]

Here is an improvement we just did, now it requires about half rendertime for the same quality of caustics: https://corona-renderer.com/comparer/0cZSSm

Will you print me the tshirt now? :D

[Image Complete]

It is 1 min vs 1.03 min. Am I missing something? :[

[Ondra]

it is same time comparison, see quality of the caustics, especially inside the ring and pool