Brute force - When...?

[3dvizual]

Hi.

 

I am a little confused about when to use brute force and when not to use it.?

 

I am specially thinking about still images.

 

Can you give me some good advice when to use this with advantage.

[Corey Beaulieu]

The only time to really utilize Brute Force is when you have an animation scene where objects are changing\moving and not just the camera.

 

Beyond this, you may see a better image quality from Brute force with things like a close up detail of hair and fur or things of that hyper detailed nature. The general reality of it though is that Brute Force is a noisy solution unless you are going to crank up the settings, in which case you are heading out on vacation after you hit render.

 

I will add that I have begun using Brute force in some testing because I believe that if the noise isn't too bad, it does create a softer render. Times are longer, but there has to be a balance somewhere.

[3dvizual]

Ok. Thanks. The reason why I ask this is because many people speaks of brute as the wrong choice, because of crazy render times.

 

But Peter Oldorf speaks about using this method to his advantage in his very nice looking night render. Seen here:

http://www.ronenbekerman.com/making-of-tomczak-house/

[Corey Beaulieu]

Thanks for sharing that. I missed it.

 

He says in there himself that it really took too long to calculate and that it was only because he had the time to wait that he used Brute Force. He also comments on the softness I mentioned.

 

My VERY GENERIC understanding is that Brute Fore is the Unbiased version of Vray. I doesn't interpolate between samples and make blurred down-sampled maps of the geometry before rendering which average the light samples of an area and remove some of the complexity. Light renders more accurately and more subtle- hence the softness.

 

In the end, I think this is the debate people have when they start talking about Maxwell as a better render engine than VRay. I don't agree, but Maxwell, among other things, is basically Brute force with some other twists in lighting.

[Scott Schroeder]

I can bet you that if Peter used anything other than brute force and used your typical vray settings, he would have gotten the same image in 1/4th the render time. It's a great image, but nothing about it screams use brute force. It was an absolute waste of time and contributed nothing to the final image. It's just my 2 cents, but brute force is idiotic for stills.

 

"For this shot one 24 core Mac calculated over 17 hours" = 100% without a doubt waste of time.

[Chris MacDonald]

Brute force I see as a luxury, for when you have plenty of time to get renders out. Other than that, it never gets used by me - and I disagree that you need to use it when you have moving objects in your scene, the irradiance map is still very much usable. In fact, aside from exceptionally fine lighting details the irradiance map will do it all - depending on how you set it up.

 

Brute force is great, because there's so little setup time involved and many see it as a get out clause instead of learning how to fine tune the irradiance map. If you just invest some time and little research/test renders into how the irradiance map works, you can get some excellent results out of it very quickly.

 

The only times I really consider using brute force is when I have a scene with either a complex lighting/indirect lighting solution or lots of fine details that get lost due to irradiance map interpolation, for example ornate mouldings/cornicing.

[3dvizual]

Thank you all. That really helped me a lot to understand the differences.

 

Chris, could you post one of your images where you have used this solution.?

[Chris MacDonald]

Where I've used brute force, or irradiance map?

[Francisco Penaloza]

I feel like jump in defense of brute force after reading some this post

IMO the main thing is know your tool deep enough to get the most of it, brute force is the precise way to calculate GI everything else is an approximation, average or interpolated way to speed up the process, there is not good or bad here, just different ways, now Glossy reflections and refraction react in a different way when you use brute force, also it works better than light cache at least as second bounce when you work with displacement or intense landscaping type of mesh, as mentioned before when you have fine details in your model, brute force will give you the right interpretation of it.

with that being said, you need to adjust V Ray in a proper way to use brute force, in that making off I am not surprised that he used Brute force as first bounce, what called my attention was that in his antialising values(very important when you use brute force) he set it up with min subdibs as 1 and max subdiv as 50 with a threshold controlled by the general VRay DMC sampler threshold, this is not efficient at all, he could put 500 as max subdivs but if the DMC sampler threshold is to high it will work until 8 subdivs maybe then it wont sample any more, if you set up you General DMC smapler so low that you get a clean brute force solution you also will push all the other noise values so high that you have double or triple your render time for not reason.

You should see Christopher Nichols video and he explain very well his workflow( he says that it is used in his animations project because quality and best solution for moving objects) of course when we talk about Movie industry render times are different than our standards, but I managed to do animations with brute force as second bounce and good still with brute force as first bounce. top artist as Bertrand Benoit, Alex Roman and others use brute force for some of their projects, to get the maximum quality, but again they are very savvy on V-RAy and the the key.

my two cents.

[Camby1298]

Whenever I tap into using Brute force I typically follow the universal settings suggestion from Chaos Group:

 

http://www.spot3d.com/vray/help/200R1/tutorials_unisettings.htm

[onyx]

I would have created a new topic but its been a year since Ive posted here so they wouldn't let me, but i am in need of some help..

 

Ive been using vray for still renderings for a 7 years now but Ive only recently begun using in for animations. I have had no problems until recently when my usual animation setup produced horrible results, the problem seems to be that i have animating objects and animating lights.. The typcial flythrough settings i use with light cache and irradiance map just dont do it...

 

Its a 3000 frame animation and its starts out with all of the lights on but with 0 intensity (vray light materials too), the lights are set up to turn on (get brighter) as the camera moves through the space to give a gradual feeling from moody to well lit. So, lights are constantly turning on through the whole animation. Doors, blinds and curtains open up as well, these are my only moving objects but they should also play with the lighting greatly..

 

Here is a pre render so you can get a clear idea of what is happening as the camera moves and keep in mind that the lighting is constantly changing.

 

 

Here is a single frame render i did with the my normal render settings

 

And here is the same frame render after i set it up for rendering an animation and calculated the light cache and the IR map the the animation.

 

It almost seems like the light cache didn't calculate any of the lighting because the animation starts with them all off? I dunno that's the only thing i could figure. Either way, its a sad result after calculating the LC and IR after 10 hours lol.

 

Here are the settings i used for this scene animation, the same i use for my normal fly through where only the camera animates.

 

 

Is this kind of animation not possible using the LC? Is brute force or some other setting the answer? Any help on this will be greatly appreciated, it took some time and thought to set this up the way i wanted, it would be a shame to end up rendering it as a standard fly through with the lights always on and only the camera animating. Thanks allot!!

[Corey Beaulieu]

Animated lights, objects, and camera in one file should be done through light cache as a secondary and single frame with Brute Force set as the primary. You could probably go 1500 on the light cache and save a few of those hours of render time. 15000 is outrageous.

 

In the IRR method, you render the irradiance as you have it setup, Multi-frame incremental and the Fly-through Light cache. Save that as a new Irr File and tick "don't render final image" while that runs. Then set your IRR to from file and load this new IRR and put secondary to none.. Don't forget to un-tick the final render thing. Also remember to put every nth frame back to 1.

 

Everything should render fine from there. But... if you are rendering from a farm system, be sure to set a dependency on the IRR. It needs to finish before your render.

 

Lasty, I'll say that you might be best off rendering in groups and 3 static exposures. Then in post do the brightening with an exposure.

[onyx]

"Animated lights, objects, and camera in one file should be done through light cache as a secondary and single frame with Brute Force set as the primary. You could probably go 1500 on the light cache and save a few of those hours of render time. 15000 is outrageous. "

 

Thanks i will definitely try this out! Ive never used BF for rendering before so i tried test it last night before i left work on the same file. I left IRR as primary and changed the LC secondary to BR ad didn't change any of the B settings( this was before i saw your post) Rendering time for that frame whent from 10 min to 3hours.. A 3000% increase in render time saw off putting to say the least lol.

 

So if i use BF as the primary and LC as the secondary, what are reasonable BF settings for this animation that wouldn't produce any noticeable grain or artifacts and at the same time wont increase the render times exponentially?? Thanks so much for the info!

 

Edit: I just wanted to clarify, LC should be set to single frame and not fly through mode? If this is the case can i render on different computers and get the same results?

Edited January 23, 2013 by onyx

[Corey Beaulieu]

BF times are tough. A good start would be 16 or 24 subdivs on the BF and 1000 on LC. Single frame LC and multiple machines is fine. BF can also benefit from fully adaptive methods. DMC adaptive amount goes to 1.0 and then the min max of your image sampler can get higher (2/16). You will want to use the color threshold instead of the noise; 0.005 or so. The rest is a hope and a prayer. BF is just tough. The noise is soft grain of anything. Preferable in some cases and not in others. Use LC on glossy rays.

[onyx]

Thanks allot man.. I settled on 30 Subs for the BF its and 1200 for the LC the grain seems barely noticable on those settings. Im gonna render out 10 seconds to view before i make a decision, if the grain bothers me then ill just revert to an earlier file with no object or light animation. Going higher in BF sub just wouldn't be worth the time, its already tripled the render time. Ill post the ten secs once they're done, thanks again!! You've been very helpful.

[onyx]

Ya know what, ive decided that 1500 hours of rendering isnt worth the effect for such a long animation, even broken up on 3 computers thats still 3 weeks. Another time maybe :'(

[Francisco Penaloza]

I just would like to clarify that if you have Lights turning on and off and moving objects, IRR Multiframe incremental is not the right options, as the name says what is does is take 2 frames IRR samples then interpolate and increment as need it, for example if you have a car moving and you use multiframe incremental as the car pass by you will get a dark stain in the ground as the shadows of the car that was there in some moment projected.

The same issue will happens with the lights on then off, what you need to use is Animation pre-pass and animation rendering. This will create a separate IRR per frame and mix as need it to eliminate flickering.

 

Now your animation is a very complex situation, the correct approach would be render your animation with light on all the time, and Light cache single frame and IRR animation, but use the light select feature of VRay and render all basic passes, Diffuse, GI, AO, Matte shadows, Reflection, Refraction, DOF, Normals, then in a post processing software such After Effects you compile and create the effect of turning on and off the lights.

 

Other approach would be use IRR Animation first bounce and Brute force second, or Brute force first bounce and Light cache second single frame, but with the values described by Corey.

 

Fco.