Brute Force Secondary Bounces? HELP!

[tarontis]

Hey everyone, this is my first post so please bear with me if I ramble

We mostly deal with office interiors, so the majority of our work is lit using the same technique.

We currently use Irradiance Map for primary and Light cache for secondary bounces, but have heard that brute force can produce better results. We also use Linear work flow gamma 2.2

We have been trying out using Lightcache on primary and bruteforce on secondary as a tutorial DVD we have been using from the Gnomon Worksop "Global Illumination : Interiors" goes into detail about using QMC to increase the amount of seconary bounces. Apparently this can allow light to penetrate further into a scene to brighten dark areas without washing out bright areas. As I understand it, Brute force is the new name for QMC?

The problem we are having however, is that while increaseing the number of subdivs for the bruteforce does increase render time and quality, increasing the secondary bounces has no effect on the amount of light, even doing something crazy just to test like increasing it from 5 to 500!

This setting is of great interest to me because I find that lighting a scene using only light from the windows creates much more realistic results, but does not penetrate far enough into the backs of the rooms, so I have to resort to adding a lot of ceiling lights, which while they do work, tend to "flatten" the scene a bit and give it less impact.

Does anyone have any advice on this? How can I increase the secondary bounces to get the results I want?

[Fekta.studio]

Perhaps you can try swapping GI engines, and use BF as primary and LC as secondary. Search in help index for Vlado Universal settings.. or follow the link bellow..

http://www.spot3d.com/vray/help/150S...nisettings.htm

[tarontis]

thanks fekta

however if i change BF as primary and LC as secondry I cannot control secondry the bounce using LC?

the secondry bounce in BF is greyed out if used for the primary engine.

how do i brighten up my scene using secondary bounces?

[SteveC]

Hi Tarontis,

I agree with fekta, use brute force as primary and light cache as secondary, with
brute force set as your primary engine the secondary bounces will be greyed out
because it is ony calculating the primary bounces, also setting brute force as primary
and light cache as secondary should speed up your rendering, rather than having the
engines the other way around.

Have you tried adjusting your camera settings?

steve

[tammo]

If you want to get the light to travel far into the room without getting burnout areas you have to use color mapping.

I would reset all your gamma settings to max default as this can cause many problems.
Then set your color mapping to reinhard with and lower the burn value to for example 0,3.

This should lighten the room up without the "washing out" you mentioned.

[tarontis]

Thanks Steve

Yea I know that this does produce faster renders, but it is the secondary bounce setting that confuses me, in theory having bruteforce for your second should enable you to simply increase the distance that the light bounces, but it doesn't seem to work, very frustrating!

I normally use Max camra's, not Vray, I know that increasing the f stop and the balance between shutter speed and film speed can affect result majorly, but would this not brighten areas which are already at the correct level, not just the dark areas?

Tammo

We normally use either Reinhard and lowered burn value, or Exponential at the moment.

Why would changing our gamma settings have an affect, isn't the point of 2.2 to spread light more evenly in the first place? Confusing

I've scanned in a couple of pages from the Vray complete guide to demonstrate the section that I am interested in, this seems to indicate that you can get some nice results simply from increasing the seconardary bounces, but I just can't get this to work, am I barking up the wrong tree perhaps? Can't seem to find any referances anywhere to give me an answer

This link also seems to say the same

http://www.spot3d.com/vray/help/150S...les_GI.htm#ex3

example 3 seems to say that increasing the light bounces can brighten a scene

Hope this gives you more of an idea of why I am so confused

Thanks a lot guys, any help is much appreciated

[SteveC]

Hi Tammo,

Yes, increasing the secondary bounces should illuminate the scene more, at the cost
of render time, I wonder if you need to use the vray camera in order to benefit from
the additional secondary bounces? I never use the max camera so I'm not sure how
using it effects how you see additional bounces.

You're right about adjusting iso and shutter speed, it does brighten the whole scene,
this is the method I use when rendering interiors, I try to think as I would if I were taking
an interior photograph. Unfortunately doing it that way does have the drawback of
washing out directly lit scene elements and any exterior viewed through windows, it's a
bit of a balacing act to get it right.

steve