Hi,
I have been testing refractions/reflections in Houdini Mantra for quite sometime now. I find the tools in the mantra renderer and shading very tempting to cast away for another renderer. And its power seems to suits more than enough my needs. But I must say it has been very difficult to find a production ready solution to use refractions. The final result is quite nice but too expensive to get a noise free image.
The image attached called GlassTest_NonTreated is at a level I will consider acceptable, but it took 2h 20' to achieve, on a 2 Xeon 2.4GHz PC. Hardly acceptable in a 3 light setup with Environment Light. Most of the noise that presents problems comes from the indirect refractions, and it is only the refraction that makes the render slow. Other types of noise is not visible enough to really bother me. But refractions are so used in motion graphics I have been purposely pushing myself to understand them and get them ready to be used. As of now I cannot say I feel confident.

I have limited refractions and reflections to 5 bounces and really focused the extra Samples only to deal with the sources of noise, a bit in the indirect reflection and a lot in the indirect refractions. I have even dig and changed the stochastic samples to probability to improve the noise.I even tested just turning off Stochastic sample (which funny how didn't show any difference….by the way funny name Sssstochastic).

Maybe I am doing something wrong, or a lot of things wrong. I am relatively new in Houdini, but by no means I will consider myself new in rendering. And that's why I feel a masterclass in rendering for non-VFX scenes (basically realistic or motion graphics) objects and surfaces rather than water and explosions would be greatly appreciated.

There are some tutorials out there but they are way too simplistic and basic.

I have included here a little test scene which I consider a perfect place to test getting rid of noise. A 2 light setup with an environment light. All shaders are from the new Principled shader and the glass shader uses the beautiful Dispersion. This set up is probably as basic as it gets but it is still quite difficult to get an acceptable level of noise on the refractions.

Again, I totally understand if I am doing something wrong….that's why a good masterclass on the subject will be nice.

Sorry for the long post, I hope you guys understand I am not trying to be antagonistic, quite the opposite I want to help improve Mantra and the User experience as much as any user can and that's why I share this experience.

add a gilight maybe useful.

wangguo
add a gilight maybe useful.

I purposely avoided the GILIGHT as I wanted to keep the example as basic as possible, without getting involved into the photon map issues. The problems anyway are mainly in the indirect refraction noise.

Nicolas Heluani

wangguo
add a gilight maybe useful.

I purposely avoided the GILIGHT as I wanted to keep the example as basic as possible, without getting involved into the photon map issues. The problems anyway are mainly in the indirect refraction noise.

Hi Nicolas,

I've been taking a look at your example scene and the full render you included in your post above. Out of curiosity, what type of timing would you expect for a render like this in whatever your preferred renderer is?

Cheers,
Scott

sakeating
Hi Nicolas,

I've been taking a look at your example scene and the full render you included in your post above. Out of curiosity, what type of timing would you expect for a render like this in whatever your preferred renderer is?

Cheers,
Scott

Hi Scott,
Thank you for taking the time.
To answer your question I wouldn't know for sure, maybe 30 - 40 min in C4D? The only comparable thing I ever made was the attached image and I think it was 15-20 min. Though granted is nothing close to what I am requiring of the rendering now. Am I waaaay off the mark? (The image below is heavily treated in post by the way, I don't have the original render now)

But I really did not meant the post to be comparison between renderers, and I realize now that it may have been taken that way, sorry. That totally missed my point. Quite the opposite, like I said I have the feeling that mantra is extremely powerful. I was just trying to say that it took me quite some digging to learn about the way to optimize renders in mantra and I am still not quite sure about a couple of things (Stochastic samples and when to increase them is one of those thing). So a basic video showing the ropes and common pitfalls as an introduction to render in Mantra will go a long way. That's why I posted this in “learning Houdini”, sorry for any misunderstanding.

Bests,
Nicolas.

Nicolas Heluani

sakeating
Hi Nicolas,

I've been taking a look at your example scene and the full render you included in your post above. Out of curiosity, what type of timing would you expect for a render like this in whatever your preferred renderer is?

Cheers,
Scott

Hi Scott,
Thank you for taking the time.
To answer your question I wouldn't know for sure, maybe 30 - 40 min in C4D? The only comparable thing I ever made was the attached image and I think it was 15-20 min. Though granted is nothing close to what I am requiring of the rendering now. Am I waaaay off the mark? (The image below is heavily treated in post by the way, I don't have the original render now)

But I really did not meant the post to be comparison between renderers, and I realize now that it may have been taken that way, sorry. That totally missed my point. Quite the opposite, like I said I have the feeling that mantra is extremely powerful. I was just trying to say that it took me quite some digging to learn about the way to optimize renders in mantra and I am still not quite sure about a couple of things (Stochastic samples and when to increase them is one of those thing). So a basic video showing the ropes and common pitfalls as an introduction to render in Mantra will go a long way. That's why I posted this in “learning Houdini”, sorry for any misunderstanding.

Bests,
Nicolas.

No problem at all, I'm just looking for some context. In c4D were you rendering with Arnold? Vray? a GPU based renderer? Different renderers can have different strengths and weaknesses.

And we are absolutely planning to do some tutorials around rendering in Houdini. I would also check out the Mantra User Guide in the docs for a good overview of Mantra and how it works.

cheers,
scott

sakeating
No problem at all, I'm just looking for some context. In c4D were you rendering with Arnold? Vray? a GPU based renderer? Different renderers can have different strengths and weaknesses.

And we are absolutely planning to do some tutorials around rendering in Houdini. I would also check out the Mantra User Guide in the docs for a good overview of Mantra and how it works.

cheers,
scott

I was just using the physical render native of C4D.

There's a trick to reducing refraction noise, but it's super annoying to implement. If you disable refract on all your lights, then the refractive object will no longer directly refract them, and will not split rays sampling lights. However refractions of your environment will no longer appear. To make up for it, you can make emissive objects that are visible to refract only. This is incredibly annoying with cube map textures, but not so bad with a typical lat-long image. Most other renderers I have experimented with won't even allow direct refractions, and require setting up emissive surrogates in this way, notably arnold and redshift are both this way.

Another setting that contributes to the noise greatly is dispersion. I know it's pretty, but it very expensive in terms of sampling requirements for low noise. In your test scene, the values you are using were also extremely high, physically plausible values are between 0.001 and 0.05 depending on the IOR. If you simply like the look, then by all means, go nuts.

jsmack
There's a trick to reducing refraction noise, but it's super annoying to implement. If you disable refract on all your lights, then the refractive object will no longer directly refract them, and will not split rays sampling lights. However refractions of your environment will no longer appear. To make up for it, you can make emissive objects that are visible to refract only. This is incredibly annoying with cube map textures, but not so bad with a typical lat-long image. Most other renderers I have experimented with won't even allow direct refractions, and require setting up emissive surrogates in this way, notably arnold and redshift are both this way.

Another setting that contributes to the noise greatly is dispersion. I know it's pretty, but it very expensive in terms of sampling requirements for low noise. In your test scene, the values you are using were also extremely high, physically plausible values are between 0.001 and 0.05 depending on the IOR. If you simply like the look, then by all means, go nuts.

Wow! that does sound complex I will give it a try. I am really focusing a lot on refractions because I is the only area in Mantra I have problems, and I am a bit of a hardheaded type that will not give up .
And thanks for the tips on dispersion aswell….