Brute Force Optimization questions... GI is so noisey but RGB looks fine?

[emartin8907]

Hi,

I am trying to optimize some render settings and have some questions...

Brute Force as Primary and Secondary is considerably faster than IM/ LC, and the RGB looks extremely similar.

When optimizing my settings I look at the Raw GI, Raw Reflection, Raw Refraction, and Lighting.. My Raw GI is insanely noisey with BF/BF, but the RGB doesn't seem to reveal this

My question is- should I care? Normally when optimizing settings I would think that's a problem but my RGB looks as clean as my IM/LC render. I'm just hesitant to use it for some reason! I'm so used to IM/LC and looking at these passes to tell me what to optimize :P If my Raw GI looked this noisey using IM/LC my RGB would look like total crap but for some reason I can get away with it in BF/BF?

Can someone shed some light on this for me?

Thanks,

Eric

[vlado]

You should be looking at the "GI" element, not the "Raw GI" one. It's normal that the raw GI is noisy - V-Ray optimizes its sampling based on the RGB output, and as long as this is fine, V-Ray doesn't care how the individual raw render elements come out.

Best regards,
Vlado

[emartin8907]

Thanks for the quick reply Valdo!

Ah silly me, I just did another render with normal GI and its considerably smoother than the raw gi.

Another question related to BF- why is it so much darker than IM/LC? I've tried upping the BF subdivs and depth to 128 & 32 and couldn't get it back to how bright it was with IM/LC

[super gnu]

id advise using BF and LC. this is the ideal choice these days. BF/BF is too slow for very little (no?) improvement in final image quality.

the reason BF/BF is darker than im/lc (or BF/LC) is that BF by default does 3 secondary bounces. even turning it up to 32 doesnt come close to LC which does 100 bounces by default.

you could turn BF secondaries up to 100 bounces and wait for a month, or just use LC like everyone else.

the reason "normal" gi ( do you mean IM /LC ?) looks smoother is its interpolated. if you are referring to BF/LC they its probably less noisy since the BF primaries are being calculated from a lightcache, which is interpolated and smooth, giving the BF engine less work to do to arrive at a clean image.

edit:

-ok i just understood you were referring to the "normal" gi pass, not another gi calculation method.

[emartin8907]

I normally stick with IM/LC myself but after some time optimizing this scene (exterior of a car lit only with dome light) I found BF/BF or even BF/LC is significantly faster and no noisier than IM/LC.

BF/BF was twice as fast, and BF/LC was about 30% faster still than IM/LC.

I tried upping BF GI Subdivs to 128 and it was still darker than IM/LC (still twice as fast though). Where are you saying to turn up BF secondaries? When I switch Secondaries to BF I lose any settings for secondaries except for the multiplier.

PS using 3.1

[super gnu]

hm.. unless 3.1 is different than on max (im a max guy) you should have a "bounces" control in your bf secondaries. its default at 3 bounces. subdivs will make almost no difference to brightness.. its the bounces that are the issue. are you sure you are looking at the "expert" interface?


ive literally never heard of a case where BF/BF is faster than BF/LC, or IM/LC. there are geological processes that are faster than BF/BF whenever ive tried it. to be fair though ive not tried it since vray 3, since BF/LC works so well.

edit: ive just noticed your scene is an exterior car shot with a domelight, so Gi is extremely easy to calculate in this case... my experience is generally with architectural interiors.. youd never go near BF/BF with a bargepole.

[emartin8907]

In Maya there isn't an 'expert mode' to reveal more control, that I know of at least? I know what you are talking about as I used Vray 3 in Max before too, I haven't seen that option in Maya and didn't think it existed in Maya. But I don't see anywhere to control secondary bounces for BF so maybe I'm missing something?

[vlado]

But I don't see anywhere to control secondary bounces for BF so maybe I'm missing something?

Take a look here:
http://docs.chaosgroup.com/display/V...I-BruteForceGI

There is a "depth" option which represents the number of bounces when using brute force as a secondary GI engine.

Best regards,
Vlado

[emartin8907]

Hmmm BF/LC even with BF depth at 64 looks no different than BF/LC with depth at default of 3. Is there a way to get that same brightness/ intensity as IM/LC with BF/LC or BF/BF?

[vlado]

Hmmm BF/LC even with BF depth at 64 looks no different than BF/LC with depth at default of 3. Is there a way to get that same brightness/ intensity as IM/LC with BF/LC or BF/BF?

It should have worked right away. Best to post a scene so that we can figure out what's wrong.

Best regards,
Vlado

[emartin8907]

It should have worked right away. Best to post a scene so that we can figure out what's wrong.

Best regards,
Vlado

Can't share this scene I will try and make a test one today though- so BF depth of 64 should affect brightness compared to a depth of 3?

[vlado]

Can't share this scene I will try and make a test one today though- so BF depth of 64 should affect brightness compared to a depth of 3?

Only if you are using BF as a secondary engine. If you are using the light cache then no. But in any case BF+LC should be the same brightness as IM+LC

Best regards,
Vlado

[emartin8907]

So I went to make a test scene and couldn't recreate this. I went back to my problem scene, loaded the default render preset to reset everything, and now I'm not having this problem. Perhaps I was just tired...

Thanks!

[beenyweenies]

Just wanted to add my own personal experience to this thread. BF/BF can actually be quite competitive in terms of speed, while producing much more reliable and consistent results (especially for animation work). But it all depends on your subject matter, format, and definition of "fast." I'm mostly involved in HD product work, with the products typically placed in interior settings, and my target render time per frame is around 25 minutes.

For me, BF/BF speed is totally acceptable when setting Subdivs Mult to 0.000 (letting Vray control subdivs), cranking the Min Shading Rate (higher values gradually improve shading/texture/noise quality vs. antialiasing quality) to something like 20-30, and then gradually working the Adaptive Threshold from .020 down until the time/quality balance is acceptable, usually around .015. I'm also doing a slight amount of grain management in post.

[emartin8907]

Wow thanks for sharing beenyweenies!

I've been having faster renders/ lower noise with lowering my thresholds to .005 and keeping min shading rate at 1, as opposed to cranking min shading and keeping threshold above .01. I need to do more experiments though that's interesting you're going as high as 20-30 for your min shading rate and your thresholds that high.

FWIW im focusing on car exteriors right now just lit with dome.

Appears min shading rate has better success with interiors- http://www.peterguthrie.net/blog/201...ersal-settings