MentalRay IBL in Large Scale Scenes - how to render this?

[steffenhoesel]

Hey guys,

 

i have a short question: Do you know how to most efficiently render large scale Scenes consisting of thousands of MR Proxy's with the Skylight IBL in Mental Ray?

 

I have created a rather huge Asteroid Field made out of polygon reduced rocks and in total there are round about 280.000 objects in MR Proxys scattered throughout the scene. One big roid in the center is the POV and has even more detail in form of MR Proxys added on top with Object Paint. The camera is flying through that field to finally reach that big Roid in the center.

 

At the moment it isnt possible for me to render this with IBL. Even if i decrease the Shadow Quality, Rendertimes on a Testframe size of 711x400 already take more than 14 minutes to complete. I need to render in 720p; so this would take even longer.

 

Do you have any tipps how to optimize this? Or is it just not possible to render such a large scene with IBL efficiently?

 

Thanks for your help!

subbz2k

[steffenhoesel]

Hey George,

 

thanks for your point on this.

 

Actually the scene isnt very dark at all. Since im planning to replace the Background later in the Post, i took an HDRI from the SIBL Archive (Walk of Fame) that gives me a really nice lighting situation over all. It is dimmed down a bit, thats right, but overall its not very dark at all. I had it a bit darker in the first place and already raised the Output of the Map, because i first thought the same as you do. But it had no effect on the render times; they are nearly the same (Output 0,3 compared to Output 1,0).

 

In the meantime, i somehow solved the problem by separating the huge amount of small Asteroids from the rest - to be able to render them in a separate Pass without IBL. This works for now. I can render the bigger Asteroids as well as the huge (and highly detailed) one in the center without problems. And after that i render the pass with just the small ones and "Skylight from FG" on instead of IBL. And finally i render everything together again, but with black on everything apart from the small roids and no FG. While having Self Illumination Mat (pure white) on the small roids to get the Mask for comping them in.

 

Although i loose some of the nice shadows because of this, i noticed that in the animation itself one cannot really see this if he/she doesnt look very close. And because there will be another POV in the meantime until the camera reaches the center (FumeFX will be this one), i think that i can live with that.

 

However, if still someone has an idea on general techniques how to thread IBL better when you have larger scenes, i would be happy to hear your opinion as well!

 

Many thanks in advance again

Steffen

[Francisco Penaloza]

IBL is slower than traditional lighting, mostly in Mental Ray. What you did is the right approach, when you are running out of memory or way longer render times. The best approach is divide the scene in passes or layers and put everything together in a comp software. Needless to say that how big production companies works, they don't put the whole Death start and millennium falcon with hundred of X wings in the same scene, they are all passes comp in Nuke or similar

Having said that, your 14 min per frame is not far fetch really, I usually render full HD frames at 25 to 40 minutes and more. When large scene you'll need more computers to render your animation, that's typical.

When your resources are limited, then you need to get practical and creative

[steffenhoesel]

hehe, yeah. a huge render farm for a huge scene is a little bit out of my budget i guess.

 

However, i cant get enough information on mental ray (and optimization of it in particular) and im always happy to hear from others experiences. And so i have the feeling that there still might be a trick hidden somewhere, to improve performance with IBL. As far as i can remember, Maya had IBL with mr for a long time exposed in the UI already and i played around with that some years ago. And if i remember right, you had a lot of options to tweak the IBL there. Im absolutely sure, that it at least were way more options, than just the one for shadow quality you have within Max. And even that is not long in there already.

 

Can it be, that you can get something done with String Options here? I have no real experience with that, but maybe you guys already tweaked something with that?! Would be nice if you could share your experiences.

 

Thx again

Steffen

Edited January 15, 2016 by steffenhoesel

[Francisco Penaloza]

Well I have not worked in any large project with Mental Ray in a long time, and maybe that's was one of the reasons that I choose other render engine, efficiency.

Still Mental Ray is very capable, from my bag of trick I can say, working with IBL I will first have a separated HDRI for illumination ( smaller blurred version) and other for reflection( larger size, small blur) and other for backgrounds(original size no included on GI). Also do not let GI to do all the work, try to use Portal Lights with Kelvin temperature color Shaders, they work as area lights but render a little faster, less noise too. Also using the old trick of ambien light with AO shader to fake GI lighting.

More hidden secrets now, there is not many, it is what it is really. Most of the advances in Mental Ray are present now in 3D Max version.

 

If you are in space( I meant the scene) you really won't need IBL, a good setup of area lights with ambien lights will do the trick very good. A good use of AO will help you a lot too.

Besides depending how fast your camera move, or the object, a good amount of motion blur and DOF will help to reduce noise.

and remember J.J. Abrams, put lots of lens flares too